JP7032115B2 - Non-aqueous electrolyte secondary battery - Google Patents

Non-aqueous electrolyte secondary battery Download PDF

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JP7032115B2
JP7032115B2 JP2017234987A JP2017234987A JP7032115B2 JP 7032115 B2 JP7032115 B2 JP 7032115B2 JP 2017234987 A JP2017234987 A JP 2017234987A JP 2017234987 A JP2017234987 A JP 2017234987A JP 7032115 B2 JP7032115 B2 JP 7032115B2
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secondary battery
active material
negative electrode
carbonate
electrode active
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JP2018116929A (en
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健太 石井
良輔 大澤
浩司 安部
圭 島本
誠 馬塲園
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Toyota Motor Corp
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Priority to KR1020180003291A priority patent/KR102150913B1/en
Priority to EP18151188.2A priority patent/EP3349288B1/en
Priority to US15/870,457 priority patent/US10535867B2/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H01M2300/0042—Four or more solvents
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Description

本発明は、リチウムイオン二次電池等の非水電解液二次電池に関する。詳しくは、非水電解液二次電池の電解液組成に関する。 The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. More specifically, the present invention relates to an electrolytic solution composition of a non-aqueous electrolytic solution secondary battery.

パソコンや携帯端末等のいわゆるポータブル電源あるいは車両駆動用電源として、非水電解液二次電池の需要が近年ますます高まっている。特に、軽量で高エネルギー密度が得られるリチウムイオン二次電池は、電気自動車、ハイブリッド自動車等の車両の駆動用高出力電源として好ましく用いられている。 In recent years, the demand for non-aqueous electrolyte secondary batteries has been increasing as a so-called portable power source for personal computers and mobile terminals or as a power source for driving vehicles. In particular, a lithium ion secondary battery that is lightweight and has a high energy density is preferably used as a high output power source for driving a vehicle such as an electric vehicle or a hybrid vehicle.

この種の二次電池に備えられる非水電解液は、電池の性能や耐久性を向上させる等の観点から溶媒および支持塩（電解質）の種類が選択され、使用されている。例えば、特許文献１には、粘度上昇を抑制することによって低温域における非水電解液のイオン伝導度を向上させることを目的として提供された、溶媒全体の１０重量％～９０重量％がエステル系溶媒であり１０重量％～９０重量％がカーボネート系溶媒であることを特徴とするリチウムイオン二次電池用非水電解液が記載されている。 As the non-aqueous electrolyte solution provided in this type of secondary battery, the type of solvent and supporting salt (electrolyte) is selected and used from the viewpoint of improving the performance and durability of the battery. For example, Patent Document 1 is provided for the purpose of improving the ionic conductivity of a non-aqueous electrolytic solution in a low temperature region by suppressing an increase in viscosity, and 10% by weight to 90% by weight of the entire solvent is ester-based. Described is a non-aqueous electrolyte solution for a lithium ion secondary battery, which is a solvent and in which 10% by weight to 90% by weight is a carbonate-based solvent.

特表２０１５－５２８６４０号公報Special Table 2015-528640

しかしながら、特許文献１に開示される技術は、－３０℃以下（例えば－４０℃～－３０℃）のような極低温域で電池を使用する場合を想定しておらず、かかる極低温域における非水電解液の挙動を検討したデータも存在しない。したがって、特許文献１に記載されるような単なるエステル系溶媒とカーボネート系溶媒とを混合するだけの着想では、かかる極低温域においても安定して良好な電池性能を実現するための非水電解液を提供することは困難である。
そこで本発明は、かかる事情に鑑みてなされたものであり、－３０℃以下（例えば－４０℃～－３０℃）のような極低温域であっても安定して良好な電池性能を発揮し得る組成の二次電池用非水電解液を提供することを目的とする。さらに本発明は、かかる非水電解液を備えた低温特性に優れる非水電解液二次電池を提供することを目的とする。 However, the technique disclosed in Patent Document 1 does not assume the case where the battery is used in a cryogenic region such as −30 ° C. or lower (for example, −40 ° C. to −30 ° C.), and in such a cryogenic region. There is no data on the behavior of non-aqueous electrolytes. Therefore, the idea of simply mixing an ester-based solvent and a carbonate-based solvent as described in Patent Document 1 is a non-aqueous electrolytic solution for achieving stable and good battery performance even in such an extremely low temperature range. Is difficult to provide.
Therefore, the present invention has been made in view of such circumstances, and stably exhibits good battery performance even in an extremely low temperature range such as −30 ° C. or lower (for example, −40 ° C. to −30 ° C.). It is an object of the present invention to provide a non-aqueous electrolyte solution for a secondary battery having a obtained composition. Further, an object of the present invention is to provide a non-aqueous electrolytic solution secondary battery provided with such a non-aqueous electrolytic solution and having excellent low temperature characteristics.

本発明者らは、リチウムイオン二次電池等の非水電解液二次電池において非水溶媒として使用され得るカーボネート系溶媒およびエステル系溶媒を種々検討した。そして、極低温域（例えば－３０℃以下）においても高い電池性能を実現し得る組成の非水電解液を創出し、本発明を完成するに至った。
即ち、ここで開示される発明は、非水溶媒と電解質とを含む非水電解液を備えた非水電解液二次電池に関しており、その非水溶媒が環状カーボネート系溶媒と、鎖状カーボネート系溶媒と、さらにエステル系溶媒とを主体として調製されたものであることを特徴とする。 The present inventors have studied various carbonate-based solvents and ester-based solvents that can be used as non-aqueous solvents in non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries. Then, a non-aqueous electrolytic solution having a composition capable of realizing high battery performance even in an extremely low temperature region (for example, −30 ° C. or lower) was created, and the present invention was completed.
That is, the invention disclosed herein relates to a non-aqueous electrolyte secondary battery provided with a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte, wherein the non-aqueous solvent is a cyclic carbonate solvent and a chain carbonate system. It is characterized in that it is prepared mainly of a solvent and an ester solvent.

ここで開示される非水電解液二次電池の好ましい一態様では、上記非水溶媒は、環状カーボネート系溶媒として少なくともエチレンカーボネート（ＥＣ）およびプロピレンカーボネート（ＰＣ）を含み、鎖状カーボネート系溶媒として少なくともジメチルカーボネート（ＤＭＣ）およびエチルメチルカーボネート（ＥＭＣ）を含み、さらにエステル系溶媒として少なくともエチルプロピオネート（ＥＰ）を含むことを特徴とする。
これら５種の溶媒を配合してなる非水電解液二次電池によると、極低温域における電池性能の向上を図ることができる。 In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous solvent contains at least ethylene carbonate (EC) and propylene carbonate (PC) as the cyclic carbonate solvent and is used as the chain carbonate solvent. It is characterized by containing at least dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), and further containing at least ethyl propionate (EP) as an ester solvent.
According to the non-aqueous electrolytic solution secondary battery containing these five kinds of solvents, it is possible to improve the battery performance in the extremely low temperature range.

ここで開示される非水電解液二次電池の特に好ましい一態様は、上記非水溶媒全体を１００ｖｏｌ％としたときのそれぞれの含有率が、
エチレンカーボネート（ＥＣ） ２０～３０ｖｏｌ％；
プロピレンカーボネート（ＰＣ） ５～１０ｖｏｌ％ ；
エチルプロピオネート（ＥＰ） ５～１０ｖｏｌ％ ；
ジメチルカーボネート（ＤＭＣ）およびエチルメチルカーボネート（ＥＭＣ）の合計、即ちＤＭＣ＋ＥＭＣ ５０～７０ｖｏｌ％；
であることを特徴とする。
かかる配合比で上記各溶媒を配合して形成された非水電解液を採用することによって、当該電解液の引火点を２１℃以上に維持させつつ、極低温域での良好な電池性能を実現した非水電解液二次電池を提供することができる。 A particularly preferable aspect of the non-aqueous electrolyte secondary battery disclosed here is that the content of each of the non-aqueous solvents is 100 vol%.
Ethylene carbonate (EC) 20-30 vol%;
Propylene carbonate (PC) 5-10 vol%;
Ethyl propionate (EP) 5-10 vol%;
The sum of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), ie DMC + EMC 50-70 vol%;
It is characterized by being.
By adopting a non-aqueous electrolytic solution formed by blending each of the above solvents in such a blending ratio, good battery performance in an extremely low temperature range is realized while maintaining the ignition point of the electrolytic solution at 21 ° C. or higher. It is possible to provide a non-aqueous electrolyte secondary battery.

ここで開示される非水電解液二次電池のさらに好ましい一態様では、上記ジメチルカーボネート（ＤＭＣ）の含有率および上記エチルメチルカーボネート（ＥＭＣ）の含有率がいずれも２５～３５ｖｏｌ％であることを特徴とする。
かかる含有率（好ましくはほぼ均等）でＤＭＣおよびＥＭＣをともに配合することにより、安定した電池性能（例えば安定したハイレート充放電）を実現する。 In a more preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the content of the dimethyl carbonate (DMC) and the content of the ethyl methyl carbonate (EMC) are both 25 to 35 vol%. It is a feature.
By blending both DMC and EMC at such a content rate (preferably substantially equal), stable battery performance (for example, stable high-rate charging / discharging) is realized.

また、ここで開示される非水電解液二次電池の特に好ましい一態様では、上記非水電解液の凝固点が－４０℃未満であることを特徴とする。
大気圧下における凝固点が－４０℃未満（より好ましくは－４５℃未満、例えば－６０℃以上－４５℃未満）となるように非水電解液を調製することにより、－３０℃以下（例えば－３０℃～－４０℃）のような極低温域における電池特性をより向上させることができる。 Further, a particularly preferable aspect of the non-aqueous electrolytic solution secondary battery disclosed herein is characterized in that the freezing point of the non-aqueous electrolytic solution is less than −40 ° C.
By preparing the non-aqueous electrolyte solution so that the freezing point under atmospheric pressure is less than −40 ° C. (more preferably less than −45 ° C., for example, −60 ° C. or higher and lower than −45 ° C.), the temperature is −30 ° C. or lower (for example, −”. It is possible to further improve the battery characteristics in an extremely low temperature region such as 30 ° C to −40 ° C).

また、ここで開示される非水電解液二次電池の特に好ましい他の一態様では、上記非水電解液の－４０℃におけるイオン伝導度（ｍＳ／ｃｍ）が１．０以上であることを特徴とする。ここでイオン伝導度の測定は、ＡＣインピーダンス法に基づく。
極低温域でのイオン伝導度を高く維持することにより、極低温域での出力特性を良好に保つことができる。 Further, in a particularly preferable other aspect of the non-aqueous electrolytic solution secondary battery disclosed here, the ionic conductivity (mS / cm) of the non-aqueous electrolytic solution at −40 ° C. is 1.0 or more. It is a feature. Here, the measurement of ionic conductivity is based on the AC impedance method.
By maintaining high ionic conductivity in the cryogenic region, it is possible to maintain good output characteristics in the cryogenic region.

ここで開示される非水電解液二次電池（例えばリチウムイオン二次電池）は、極低温域（例えば－４０℃～－３０℃）で良好な電池性能を発揮し得る。したがって、例えば極低温域においてモーター駆動のための電力を供給し、高い性能が要求される寒冷地での車両駆動用電源として好適に使用することができる。 The non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) disclosed here can exhibit good battery performance in an extremely low temperature range (for example, −40 ° C. to −30 ° C.). Therefore, for example, it can supply electric power for driving a motor in an extremely low temperature region and can be suitably used as a power source for driving a vehicle in a cold region where high performance is required.

ここで開示される非水電解液二次電池の一実施形態（リチウムイオン二次電池）における電池外形を模式的に示す斜視図である。It is a perspective view which shows typically the outline of the battery in one Embodiment (lithium ion secondary battery) of the non-aqueous electrolytic solution secondary battery disclosed here. 図１中のＩＩ－ＩＩ線に沿う縦断面図である。It is a vertical sectional view along the line II-II in FIG. 一実施形態に係る捲回電極体の構成を示す模式図である。It is a schematic diagram which shows the structure of the winding electrode body which concerns on one Embodiment.

以下、ここで開示される非水電解液二次電池の好適な一実施形態として、密閉構造の角型リチウムイオン二次電池の構成について、図面を参照しつつ詳細に説明する。本明細書において特に言及している事項以外の事柄であって実施に必要な事柄は、当該分野における従来技術に基づく当業者の設計事項として把握され得る。本発明は、本明細書に開示されている内容と当該分野における技術常識とに基づいて実施することができる。
なお、本明細書および特許請求の範囲において数値範囲をＡ～Ｂ（ここでＡ，Ｂは任意の数値）と記載している場合は、一般的な解釈と同様であり、Ａ以上Ｂ以下を意味するものである。 Hereinafter, as a preferred embodiment of the non-aqueous electrolytic solution secondary battery disclosed herein, the configuration of a square lithium ion secondary battery having a closed structure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art.
When the numerical range is described as A to B (where A and B are arbitrary numerical values) in the present specification and claims, the general interpretation is the same, and A or more and B or less are used. It means.

本明細書において「非水電解液二次電池」とは、電解液を構成する溶媒が非水系溶媒（即ち有機溶媒）を主として構成された二次電池をいう。ここで「二次電池」は、充放電可能で所定の電気エネルギーを繰り返し取り出し得る蓄電装置をいう。例えば、非水電解液中のアルカリ金属イオンが電荷の移動を担うリチウムイオン二次電池、ナトリウムイオン二次電池等は、ここでいう非水電解液二次電池に包含される典型例である。
「電極体」とは、正極、負極、および正負極間にセパレータとして機能し得る多孔質絶縁層を含む電池の主体を成す構造体をいう。「正極活物質」または「負極活物質」（これらを総称して「電極活物質」という場合がある。）は、電荷担体となる化学種（例えば、リチウムイオン二次電池においてはリチウムイオン、ナトリウムイオン二次電池においてはナトリウムイオン）を可逆的に吸蔵および放出可能な化合物（正極活物質または負極活物質）をいう。 As used herein, the term "non-aqueous electrolyte secondary battery" refers to a secondary battery in which the solvent constituting the electrolytic solution is mainly composed of a non-aqueous solvent (that is, an organic solvent). Here, the "secondary battery" refers to a power storage device that can be charged and discharged and can repeatedly take out a predetermined electric energy. For example, a lithium ion secondary battery, a sodium ion secondary battery, and the like in which alkali metal ions in the non-aqueous electrolytic solution carry the charge transfer are typical examples included in the non-aqueous electrolytic solution secondary battery referred to here.
The "electrode body" refers to a structure constituting the main body of a battery including a positive electrode, a negative electrode, and a porous insulating layer that can function as a separator between the positive and negative electrodes. The "positive electrode active material" or "negative electrode active material" (these may be collectively referred to as "electrode active material") is a chemical substance that serves as a charge carrier (for example, lithium ion or sodium in a lithium ion secondary battery). In an ion secondary battery, it refers to a compound (positive electrode active material or negative electrode active material) capable of reversibly storing and releasing sodium ions.

以下、非水電解液二次電池の典型例として、捲回電極体および非水電解液を角型形状の電池ケースに収容した構成のリチウムイオン二次電池に対して本発明を適用する場合を主として本発明の実施形態を具体的に説明するが、本発明をかかる実施形態に限定することを意図したものではない。
例えば、捲回電極体は一例であり、本発明の技術思想は、その他の形状（例えば積層型の電極体）にも適用される。また、非水電解液二次電池の形状（外形やサイズ）には特に制限はない。 Hereinafter, as a typical example of a non-aqueous electrolytic solution secondary battery, a case where the present invention is applied to a lithium ion secondary battery having a structure in which a wound electrode body and a non-aqueous electrolytic solution are housed in a square-shaped battery case. The embodiment of the present invention will be described in detail, but the present invention is not intended to be limited to such an embodiment.
For example, the wound electrode body is an example, and the technical idea of the present invention is also applied to other shapes (for example, a laminated electrode body). Further, the shape (outer shape and size) of the non-aqueous electrolyte secondary battery is not particularly limited.

図１および図２に示すように、本実施形態に係るリチウムイオン二次電池１００は、扁平に捲回された形態の電極体（捲回電極体）２０が、非水電解液とともに扁平な角型（箱形）形状の電池ケース３０に収容された構成を有する。
電池ケース３０は、上端が開放された扁平な直方体形状の電池ケース本体３２と、その開口部を塞ぐ蓋体３４とを備える。電池ケース３０の上面（すなわち蓋体３４）には、捲回電極体２０の正極と電気的に接続する外部接続用の正極端子４２、および捲回電極体２０の負極と電気的に接続する負極端子４４が設けられている。蓋体３４にはまた、従来のリチウムイオン二次電池の電池ケースと同様に、電池ケース３０の内部で発生したガスを電池ケース３０の外部に排出するための安全弁３６が備えられている。
電池ケース３０の材質としては、アルミニウム、スチール等の金属材料；ポリフェニレンサルファイド樹脂、ポリイミド樹脂等の樹脂材料；が例示される。ケースの形状（容器の外形）は、例えば円形（円筒形、コイン形、ボタン形）、六面体形（直方体形、立方体形）、袋体形、およびそれらを加工し変形させた形状等であってもよい。 As shown in FIGS. 1 and 2, in the lithium ion secondary battery 100 according to the present embodiment, the electrode body (rolled electrode body) 20 in the form of being wound flat has a flat angle together with the non-aqueous electrolytic solution. It has a configuration housed in a mold (box-shaped) battery case 30.
The battery case 30 includes a flat rectangular parallelepiped battery case main body 32 having an open upper end, and a lid 34 that closes the opening thereof. On the upper surface of the battery case 30 (that is, the lid 34), a positive electrode terminal 42 for external connection that is electrically connected to the positive electrode of the wound electrode body 20 and a negative electrode that is electrically connected to the negative electrode of the wound electrode body 20. The terminal 44 is provided. The lid 34 is also provided with a safety valve 36 for discharging the gas generated inside the battery case 30 to the outside of the battery case 30, as in the battery case of the conventional lithium ion secondary battery.
Examples of the material of the battery case 30 include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin; The shape of the case (outer shape of the container) may be, for example, a circle (cylindrical shape, coin shape, button shape), a hexahedron shape (rectangular parallelepiped shape, cubic shape), a bag body shape, or a shape obtained by processing and deforming them. good.

図３に示すように、本実施形態に係る捲回電極体２０は、組み立てる前段階において長尺状のシート構造（シート状電極体）を有している。かかる捲回電極体２０は、長尺状のアルミニウム等の金属製の正極集電体５２の片面または両面（ここでは両面）に長手方向に沿って正極活物質層５４が形成された正極シート５０と、長尺状の銅等の金属製の負極集電体６２の片面または両面（ここでは両面）に長手方向に沿って負極活物質層６４が形成された負極シート６０とを、長尺状のセパレータシート７０を介して重ね合わせて長尺方向に捲回し扁平形状に成形されている。
捲回電極体２０の捲回軸方向における中央部分には、捲回コア部分（すなわち、正極シート５０の正極活物質層５４と、負極シート６０の負極活物質層６４と、セパレータシート７０とが密に積層された部分）が形成されている。また、捲回電極体２０の捲回軸方向の両端部では、正極シート５０における正極活物質層非形成部５２ａおよび負極シート６０における負極活物質層非形成部６２ａが、それぞれ捲回コア部分から外方にはみ出ている。かかる正極活物質層非形成部５２ａおよび負極活物質層非形成部６２ａには、正極集電板４２ａおよび負極集電板４４ａがそれぞれ付設され、正極端子４２（図２）および負極端子４４（図２）とそれぞれ電気的に接続されている。 As shown in FIG. 3, the wound electrode body 20 according to the present embodiment has a long sheet structure (sheet-shaped electrode body) before assembling. The wound electrode body 20 is a positive electrode sheet 50 in which a positive electrode active material layer 54 is formed along the longitudinal direction on one side or both sides (here, both sides) of a positive electrode current collector 52 made of a metal such as long aluminum. And the negative electrode sheet 60 in which the negative electrode active material layer 64 is formed along the longitudinal direction on one side or both sides (here, both sides) of the long negative electrode current collector 62 made of a metal such as copper. It is formed into a flat shape by being overlapped with each other via a separator sheet 70 and wound in a long direction.
At the central portion of the wound electrode body 20 in the winding axis direction, a wound core portion (that is, a positive electrode active material layer 54 of the positive electrode sheet 50, a negative electrode active material layer 64 of the negative electrode sheet 60, and a separator sheet 70 are provided. A densely laminated portion) is formed. Further, at both ends of the wound electrode body 20 in the winding axis direction, the positive electrode active material layer non-forming portion 52a in the positive electrode sheet 50 and the negative electrode active material layer non-forming portion 62a in the negative electrode sheet 60 are respectively from the winding core portion. It sticks out to the outside. A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are attached to the positive electrode active material layer non-forming portion 52a and the negative electrode active material layer non-forming portion 62a, respectively, and the positive electrode terminal 42 (FIG. 2) and the negative electrode terminal 44 (FIG. 2). It is electrically connected to 2) respectively.

正極活物質層５４は、少なくとも正極活物質を含んでいる。正極活物質としては、リチウムイオン二次電池の正極活物質として使用し得る各種の材料の１種または２種以上を、特に限定なく採用し得る。好適例として、層状系、スピネル系等のリチウム複合金属酸化物（ＬｉＮｉＯ２、ＬｉＣｏＯ２、ＬｉＦｅＯ２、ＬｉＭｎ２Ｏ４、ＬｉＮｉ０．５Ｍｎ１．５Ｏ４，ＬｉＣｒＭｎＯ４、ＬｉＦｅＰＯ４等）が挙げられる。例えば、構成元素としてＬｉ，Ｎｉ，ＣｏおよびＭｎを含む層状構造（典型的には、六方晶系に属する層状岩塩型構造）のリチウムニッケルコバルトマンガン複合酸化物（例えば、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２）は、熱安定性に優れ、且つ理論エネルギー密度が高い好適例である。 The positive electrode active material layer 54 contains at least the positive electrode active material. As the positive electrode active material, one or more of various materials that can be used as the positive electrode active material of the lithium ion secondary battery can be adopted without particular limitation. Suitable examples include layered and spinel-based lithium composite metal oxides (LiNiO 2 , LiCoO 2 , LiFeO 2 , LiMn 2 O 4 , LiNi 0.5 Mn 1.5 O 4 , LiCrMnO 4 , LiFePO 4 , etc.). Can be mentioned. For example, a lithium nickel cobalt-cobalt manganese composite oxide (eg, LiNi 1/3 Co 1 / ) of a layered structure (typically a layered rock salt type structure belonging to a hexagonal system) containing Li, Ni, Co and Mn as constituent elements. 3 Mn 1/3 O 2 ) is a good example of excellent thermal stability and high theoretical energy density.

正極活物質の性状は特に限定されないが、例えば粒子状や粉末状であり得る。かかる粒子状正極活物質の平均粒径は、２０μｍ以下（典型的には１μｍ～２０μｍ、例えば５μｍ～１５μｍ）であり得る。また、比表面積は０．１ｍ２／ｇ以上（典型的には０．７ｍ２／ｇ以上、例えば０．８ｍ２／ｇ以上）であって、５ｍ２／ｇ以下（典型的には１．３ｍ２／ｇ以下、例えば１．２ｍ２／ｇ以下）であり得る。なお、本明細書において「平均粒径」とは一般的なレーザー回折・光散乱法に基づく粒度分布測定により測定した体積基準の粒度分布おいて、微粒子側からの累積５０％に相当する粒径（Ｄ５０粒径、メジアン径ともいう。）をいう。 The properties of the positive electrode active material are not particularly limited, but may be, for example, in the form of particles or powder. The average particle size of the particulate positive electrode active material can be 20 μm or less (typically 1 μm to 20 μm, for example 5 μm to 15 μm). The specific surface area is 0.1 m 2 / g or more (typically 0.7 m 2 / g or more, for example 0.8 m 2 / g or more) and 5 m 2 / g or less (typically 1. It can be 3 m 2 / g or less, for example 1.2 m 2 / g or less). In the present specification, the "average particle size" is a particle size corresponding to the cumulative 50% from the fine particle side in the volume-based particle size distribution measured by the particle size distribution measurement based on a general laser diffraction / light scattering method. ( D50 particle size, also referred to as median diameter).

正極活物質層５４には、上記正極活物質に加え、一般的なリチウムイオン二次電池において正極活物質層５４の構成成分として使用され得る１種または２種以上の材料を必要に応じて含有し得る。そのような材料の例として、導電材やバインダが挙げられる。導電材としては、例えば、種々のカーボンブラック（典型的にはアセチレンブラック、ケッチェンブラック）、コークス、活性炭、黒鉛、炭素繊維、カーボンナノチューブ等の炭素材料を好適に用いることができる。また、バインダとしては、例えば、ポリフッ化ビニリデン（ＰＶｄＦ）等のハロゲン化ビニル樹脂；ポリエチレンオキサイド（ＰＥＯ）等のポリアルキレンオキサイド；等を好適に用いることができる。 In addition to the above-mentioned positive electrode active material, the positive electrode active material layer 54 contains one or more kinds of materials that can be used as constituents of the positive electrode active material layer 54 in a general lithium ion secondary battery, if necessary. Can be. Examples of such materials include conductive materials and binders. As the conductive material, for example, various carbon materials such as carbon black (typically acetylene black and ketjen black), coke, activated carbon, graphite, carbon fiber, and carbon nanotubes can be preferably used. Further, as the binder, for example, a vinyl halide resin such as polyvinylidene fluoride (PVdF); a polyalkylene oxide such as polyethylene oxide (PEO); or the like can be preferably used.

正極活物質層５４全体に占める正極活物質の割合は、凡そ６０質量％以上（典型的には６０質量％～９９質量％）とすることが適当であり、通常は凡そ７０質量％～９５質量％であることが好ましい。導電材を使用する場合、正極活物質層５４全体に占める導電材の割合は、例えば凡そ２質量％～２０質量％とすることができ、通常は凡そ３質量％～１０質量％とすることが好ましい。バインダを使用する場合、正極活物質層５４全体に占めるバインダの割合は、例えば凡そ０．５質量％～１０質量％とすることができ、通常は凡そ１質量％～５質量％とすることが好ましい。
正極活物質層５４の片面当たりの平均厚みは、例えば２０μｍ以上（典型的には４０μｍ以上、好ましくは５０μｍ以上）であって、１００μｍ以下（典型的には８０μｍ以下）であり得る。また、正極活物質層５４の密度は、例えば１ｇ／ｃｍ３～４ｇ／ｃｍ３（例えば１．５ｇ／ｃｍ３～３．５ｇ／ｃｍ３）であり得る。また、正極活物質層５４の空隙率（空孔率）は、例えば１０～５０ｖｏｌ％（典型的には２０～４０ｖｏｌ％）であり得る。このような性状を満たすことにより、正極活物質層５４内に適度な空隙を保つことができ、非水電解液を十分に浸潤させることができる。このため、電荷担体との反応場を広く確保することができ、極低温域であっても高い入出力特性を発揮することができる。なお、本明細書において「空隙率」とは、水銀ポロシメータの測定によって得られた全細孔容積（ｃｍ３）を活物質層の見かけの体積（ｃｍ３）で除して１００を掛けた値をいう。 It is appropriate that the ratio of the positive electrode active material to the entire positive electrode active material layer 54 is 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 preferable. When a conductive material is used, the ratio of the conductive material to the entire positive electrode active material layer 54 can be, for example, approximately 2% by mass to 20% by mass, and usually approximately 3% by mass to 10% by mass. preferable. When a binder is used, the ratio of the binder to the entire positive electrode active material layer 54 can be, for example, about 0.5% by mass to 10% by mass, and usually about 1% by mass to 5% by mass. preferable.
The average thickness of the positive electrode active material layer 54 per one side may be, for example, 20 μm or more (typically 40 μm or more, preferably 50 μm or more) and 100 μm or less (typically 80 μm or less). The density of the positive electrode active material layer 54 may be, for example, 1 g / cm 3 to 4 g / cm 3 (for example, 1.5 g / cm 3 to 3.5 g / cm 3 ). Further, the porosity (porosity) of the positive electrode active material layer 54 can be, for example, 10 to 50 vol% (typically 20 to 40 vol%). By satisfying such properties, an appropriate void can be maintained in the positive electrode active material layer 54, and the non-aqueous electrolytic solution can be sufficiently infiltrated. Therefore, a wide reaction field with the charge carrier can be secured, and high input / output characteristics can be exhibited even in a cryogenic region. In the present specification, the "void ratio" is a value obtained by dividing the total pore volume (cm 3 ) obtained by the measurement of the mercury porosity by the apparent volume (cm 3 ) of the active material layer and multiplying by 100. To say.

正極シート５０を作製する方法は特に限定されない。例えば、正極活物質と必要に応じて用いられる材料とを適当な溶媒（例えばＮ－メチル－２－ピロリドン）に分散させ、スラリー状またはペースト状の組成物（以下「正極活物質層形成用スラリー」という。）を調製する。かかる正極活物質層形成用スラリーを長尺状の正極集電体５２に付与し、該スラリーに含まれる溶媒を除去、乾燥し、必要に応じてプレスすることにより、正極集電体５２上に所望の性状の正極活物質層５４を備えた正極シート５０を作製することができる。 The method for producing the positive electrode sheet 50 is not particularly limited. For example, a positive electrode active material and a material used as needed are dispersed in an appropriate solvent (for example, N-methyl-2-pyrrolidone) to form a slurry-like or paste-like composition (hereinafter, “slurry for forming a positive electrode active material layer”). ") Is prepared. The slurry for forming the positive electrode active material layer is applied to the long positive electrode current collector 52, the solvent contained in the slurry is removed, dried, and pressed as necessary, thereby forming the positive electrode current collector 52 onto the positive electrode current collector 52. A positive electrode sheet 50 provided with the positive electrode active material layer 54 having desired properties can be produced.

一方、負極活物質層６４は、少なくとも負極活物質を含んでいる。負極活物質としては、リチウムイオン二次電池の負極活物質として使用し得る各種の材料の１種または２種以上を、特に限定なく使用することができる。好適例として、黒鉛（グラファイト）、難黒鉛化炭素（ハードカーボン）、易黒鉛化炭素（ソフトカーボン）、カーボンナノチューブ、これらを組み合わせた構造を有するもの等の少なくとも一部にグラファイト構造（層状構造）を含む炭素材料が挙げられる。高エネルギー密度が得られることから、天然黒鉛（石墨）や人造黒鉛等の黒鉛系材料を好ましく用いることができる。
負極活物質として、特に黒鉛の表面に非晶質炭素（アモルファスカーボン）を備えた非晶質コート黒鉛系材料の使用が好ましい。かかる非晶質コートの形成方法としては、例えば、核材（黒鉛粒子）表面に気相のコート原料を、不活性ガス雰囲気下において蒸着させるＣＶＤ法のような気相法、コート原料を適当な溶媒で希釈してなる溶液を核材に混ぜ合わせた後、不活性ガス雰囲気下において、該コート原料を焼成・炭化させる液相法、核材およびコート原料を、溶媒を用いずに混練した後、不活性ガス雰囲気下において焼成・炭化させる固相法、等の従来公知の方法を適宜採用することができる。 On the other hand, the negative electrode active material layer 64 contains at least the negative electrode active material. As the negative electrode active material, one or more of various materials that can be used as the negative electrode active material of the lithium ion secondary battery can be used without particular limitation. As a preferred example, graphite (graphite), non-graphitizable carbon (hard carbon), easily graphitized carbon (soft carbon), carbon nanotubes, those having a structure combining these, and the like have a graphite structure (layered structure) in at least a part thereof. Examples include carbon materials containing. Since a high energy density can be obtained, graphite-based materials such as natural graphite (stone ink) and artificial graphite can be preferably used.
As the negative electrode active material, it is particularly preferable to use an amorphous coated graphite-based material having amorphous carbon (amorphous carbon) on the surface of graphite. As a method for forming such an amorphous coat, for example, a vapor phase method such as a CVD method in which a vapor phase coating raw material is vapor-deposited on the surface of a core material (graphite particles) in an inert gas atmosphere, or a coating material is suitable. After mixing the solution diluted with a solvent with the core material, the liquid phase method for firing and carbonizing the coating material in an inert gas atmosphere, the core material and the coating material are kneaded without using a solvent. , A conventionally known method such as a solid phase method of firing and carbonizing in an inert gas atmosphere can be appropriately adopted.

負極活物質の性状は特に限定されないが、例えば粒子状や粉末状であり得る。かかる粒子状負極活物質の平均粒径は、例えば５０μｍ以下（典型的には２０μｍ以下、例えば１μｍ～２０μｍ、好ましくは５μｍ～１５μｍ）であり得る。また、比表面積は１ｍ２／ｇ以上（典型的には２．５ｍ２／ｇ以上、例えば２．８ｍ２／ｇ以上）であって、１０ｍ２／ｇ以下（典型的には３．５ｍ２／ｇ以下、例えば３．４ｍ２／ｇ以下）であり得る。 The properties of the negative electrode active material are not particularly limited, but may be, for example, in the form of particles or powder. The average particle size of the particulate negative electrode active material can be, for example, 50 μm or less (typically 20 μm or less, for example, 1 μm to 20 μm, preferably 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 2.8 m 2 / g or more) and 10 m 2 / g or less (typically 3.5 m 2 ). It can be less than / g, for example 3.4 m 2 / g or less).

負極活物質層６４には、上記負極活物質に加え、一般的なリチウムイオン二次電池において負極活物質層の構成成分として使用され得る１種または２種以上の材料を必要に応じて含有し得る。そのような材料の例として、バインダや各種添加剤が挙げられる。バインダとしては、例えば、スチレンブタジエンゴム（ＳＢＲ）、ポリフッ化ビニリデン（ＰＶｄＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等のポリマー材料を好適に用いることができる。その他、増粘剤、分散剤、導電材等の各種添加剤を適宜使用することもでき、例えば増粘剤としてはカルボキシメチルセルロース（ＣＭＣ）やメチルセルロース（ＭＣ）を好適に用いることができる。 In addition to the above-mentioned negative electrode active material, the negative electrode active material layer 64 contains one or more kinds of materials that can be used as constituents of the negative electrode active material layer in a general lithium ion secondary battery, if necessary. obtain. Examples of such materials include binders and various additives. As the binder, for example, a polymer material such as styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), or polytetrafluoroethylene (PTFE) can be preferably 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 preferably used as the thickener.

負極活物質層６４全体に占める負極活物質の割合は、凡そ５０質量％以上とすることが適当であり、通常は９０質量％～９９質量％（例えば９５質量％～９９質量％）とすることが好ましい。バインダを使用する場合には、負極活物質層６４全体に占めるバインダの割合は例えば凡そ１質量％～１０質量％とすることができ、通常は凡そ１質量％～５質量％とすることが好ましい。
負極活物質層６４の片面当たりの平均厚みは、例えば４０μｍ以上（典型的には５０μｍ以上）であって、１００μｍ以下（典型的には８０μｍ以下）とすることができる。また、負極活物質層６４の密度は、例えば０．５ｇ／ｃｍ３～２ｇ／ｃｍ３（典型的には１ｇ／ｃｍ３～１．５ｇ／ｃｍ３）程度とすることができる。また、負極活物質層６４の空隙率は、例えば５～５０ｖｏｌ％（好ましくは３５～５０ｖｏｌ％）程度であり得る。また、このような性状を満たすことにより、負極活物質層６４内に適度な空隙を保つことができ、非水電解液を十分に浸潤させることができる。このため、電荷担体との反応場を広く確保することができ、極低温域であっても高い入出力特性を発揮することができる。 It is appropriate that the ratio of the negative electrode active material to the entire negative electrode active material layer 64 is about 50% by mass or more, and usually 90% by mass to 99% by mass (for example, 95% by mass to 99% by mass). Is preferable. When a binder is used, the ratio of the binder to the entire negative electrode active material layer 64 can be, for example, approximately 1% by mass to 10% by mass, and usually preferably approximately 1% by mass to 5% by mass. ..
The average thickness of the negative electrode active material layer 64 per one side is, for example, 40 μm or more (typically 50 μm or more), and can be 100 μm or less (typically 80 μm or less). The density of the negative electrode active material layer 64 can be, for example, about 0.5 g / cm 3 to 2 g / cm 3 (typically 1 g / cm 3 to 1.5 g / cm 3 ). The porosity of the negative electrode active material layer 64 may be, for example, about 5 to 50 vol% (preferably 35 to 50 vol%). Further, by satisfying such properties, an appropriate void can be maintained in the negative electrode active material layer 64, and the non-aqueous electrolytic solution can be sufficiently infiltrated. Therefore, a wide reaction field with the charge carrier can be secured, and high input / output characteristics can be exhibited even in a cryogenic region.

負極シート６０を作製する方法は特に限定されない。例えば、負極活物質と必要に応じて用いられる材料とを適当な溶媒（例えば蒸留水）に分散させ、スラリー状またはペースト状の組成物（以下「負極活物質層形成用スラリー」という。）を調製する。かかる負極活物質層形成用スラリーを長尺状の負極集電体６２に付与し、該スラリーに含まれる溶媒を除去、乾燥し、必要に応じてプレスすることにより、負極集電体６２上に負極活物質層６４を備えた負極シート６０を作製することができる。 The method for producing the negative electrode sheet 60 is not particularly limited. For example, a negative electrode active material and a material used as needed are dispersed in an appropriate solvent (for example, distilled water) to obtain a slurry-like or paste-like composition (hereinafter referred to as “slurry for forming a negative electrode active material layer”). Prepare. The slurry for forming the negative electrode active material layer is applied to the long negative electrode current collector 62, the solvent contained in the slurry is removed, dried, and pressed as necessary on the negative electrode current collector 62. A negative electrode sheet 60 provided with the negative electrode active material layer 64 can be manufactured.

正負極シート５０、６０間に介在されるセパレータシート７０としては、正極活物質層５４と負極活物質層６４とを絶縁するとともに非水電解液の保持機能やシャットダウン機能を有するものであればよい。好適例として、ポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）、ポリエステル、セルロース、ポリアミド等の樹脂から成る多孔質樹脂シート（フィルム）が挙げられる。
セパレータシート７０の性状は特に限定されない。例えば、平均厚みは、通常、１０μｍ以上（典型的には１５μｍ以上、例えば１７μｍ以上）であって、４０μｍ以下（典型的には３０μｍ以下、例えば２５μｍ以下）であることが好ましい。 The separator sheet 70 interposed between the positive and negative electrode sheets 50 and 60 may be any as long as it insulates the positive electrode active material layer 54 and the negative electrode active material layer 64 and has a function of holding a non-aqueous electrolyte solution and a function of shutting down. .. Preferable examples include a porous resin sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide.
The properties of the separator sheet 70 are not particularly limited. For example, the average thickness is usually preferably 10 μm or more (typically 15 μm or more, for example 17 μm or more) and 40 μm or less (typically 30 μm or less, for example 25 μm or less).

次に、本実施形態に係る非水電解液について詳細に説明する。
非水電解液は、非水溶媒と、電解質（即ち支持塩）とから構成され、かかる非水溶媒は、環状カーボネート系溶媒と、鎖状カーボネート系溶媒と、さらにエステル系溶媒とを主体として調製される。
環状カーボネート系溶媒と、鎖状カーボネート系溶媒とを共存させることにより、好適な高誘電率と低粘度とを両立させることができる。また、さらにエステル系溶媒を共存させることにより、凝固点（および融点）を低下させ、低温域での好適な電池使用を図ることができる。 Next, the non-aqueous electrolytic solution according to the present embodiment will be described in detail.
The non-aqueous electrolyte solution is composed of a non-aqueous solvent and an electrolyte (that is, a supporting salt), and the non-aqueous solvent is mainly prepared of a cyclic carbonate-based solvent, a chain carbonate-based solvent, and an ester-based solvent. Will be done.
By coexisting the cyclic carbonate solvent and the chain carbonate solvent, it is possible to achieve both a suitable high dielectric constant and a low viscosity. Further, by coexisting with an ester solvent, the freezing point (and melting point) can be lowered, and a suitable battery can be used in a low temperature range.

好ましくは、環状カーボネート系溶媒として少なくともエチレンカーボネート（ＥＣ）およびプロピレンカーボネート（ＰＣ）を含む。比誘電率の高いＥＣと凝固点（および融点）の低いＰＣの組合せは、極低温域における電池性能の向上に寄与する。さらに、ＰＣの添加は、耐久性（例えば保存特性やサイクル特性）を向上させるという観点からも好ましい。
また、好ましくは、鎖状カーボネートとして少なくともジメチルカーボネート（ＤＭＣ）およびエチルメチルカーボネート（ＥＭＣ）を含む。酸化電位が高い（電位窓の広い）ＤＭＣとＥＭＣの組合せは、電池性能を向上させるという観点からも好ましい。
また、好ましくは、エステル系溶媒として少なくともエチルプロピオネート（ＥＰ）を含む。ＥＰの添加により、非水電解液の凝固点（および融点）と低温域における粘度の低下を好適に図ることができる。さらに、ＰＣと組み合わせてＥＰを添加することによって、耐久性（例えば保存特性やサイクル特性）を良好に向上させることができる。
これら５種の溶媒を共存させた非水電解液によると、極低温域（例えば－４０℃～－３０℃）のような極低温域であっても安定して良好な性能（例えば良好な出力維持）を実現することができる。さらに、耐久特性（例えばサイクル特性、保存特性）を向上させることができる。 Preferably, the cyclic carbonate solvent contains at least ethylene carbonate (EC) and propylene carbonate (PC). The combination of EC with a high relative permittivity and PC with a low freezing point (and melting point) contributes to the improvement of battery performance in the extremely low temperature range. Furthermore, the addition of PC is also preferable from the viewpoint of improving durability (for example, storage characteristics and cycle characteristics).
Further, preferably, at least dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are contained as the chain carbonate. The combination of DMC and EMC having a high oxidation potential (wide potential window) is also preferable from the viewpoint of improving battery performance.
Further, it preferably contains at least ethyl propionate (EP) as an ester solvent. By adding EP, it is possible to suitably reduce the freezing point (and melting point) of the non-aqueous electrolytic solution and the viscosity in the low temperature range. Furthermore, by adding EP in combination with PC, durability (for example, storage characteristics and cycle characteristics) can be satisfactorily improved.
According to the non-aqueous electrolytic solution in which these five kinds of solvents coexist, stable and good performance (for example, good output) even in a cryogenic region such as a cryogenic region (for example, -40 ° C to -30 ° C). Maintenance) can be realized. Further, durability characteristics (for example, cycle characteristics, storage characteristics) can be improved.

さらに好ましくは、非水溶媒全体を１００ｖｏｌ％としたときの上記５種の溶媒それぞれの含有率が、
ＥＣ ２０～３０ｖｏｌ％、
ＰＣ ５～１５ｖｏｌ％（例えば５～１０ｖｏｌ％または１０～１５ｖｏｌ％）、
ＥＰ ５～１５ｖｏｌ％（例えば５～１０ｖｏｌ％または１０～１５ｖｏｌ％）および
ＤＭＣとＥＭＣの合計 ５０～７０ｖｏｌ％、
となるように非水電解液を調製する。
このような組成の非水電解液によると、当該電解液の引火点を２１℃以上に維持させつつ、極低温域での良好な電池性能を実現することができる。ＰＣとＥＰの含有率がそれぞれ５～１０ｖｏｌ％であることが特に好ましい。さらに、良好な耐久性（例えば保存特性、サイクル特性）を実現することができる。 More preferably, the content of each of the above five kinds of solvents when the total amount of the non-aqueous solvent is 100 vol% is
EC 20-30 vol%,
PC 5-15 vol% (eg 5-10 vol% or 10-15 vol%),
EP 5 to 15 vol% (eg 5 to 10 vol% or 10 to 15 vol%) and DMC and EMC total 50 to 70 vol%,
Prepare a non-aqueous electrolyte solution so as to be.
According to the non-aqueous electrolytic solution having such a composition, good battery performance in an extremely low temperature range can be realized while maintaining the flash point of the electrolytic solution at 21 ° C. or higher. It is particularly preferable that the contents of PC and EP are 5 to 10 vol%, respectively. Further, good durability (for example, storage characteristics, cycle characteristics) can be realized.

上記５種の溶媒を主として非水電解液が調製される限りにおいて、その他の有機溶媒成分を含有させてもよい。
そのような添加可能な任意成分としては、例えば、環状カーボネート系溶媒である１，２－ブチレンカーボネート、２，３－ブチレンカーボネート、１，２－ペンチレンカーボネート、２，３－ペンチレンカーボネート、４－フルオロ－１，３－ジオキソラン－２－オン、トランス又はシス－４，５－ジフルオロ－１，３－ジオキソラン－２－オン、ビニレンカーボネート、ビニルエチレンカーボネート、４－エチニル－１，３－ジオキソラン－２－オン、等が挙げられる。
また、添加可能な他の種類の任意成分として、鎖状カーボネート系溶媒であるジエチルカーボネート、ジプロピルカーボネート、メチルプロピルカーボネート、メチルイソプロピルカーボネート、エチルプロピルカーボネート、メチルブチルカーボネート、ジブチルカーボネート、等が挙げられる。
また、添加可能な他の種類の任意成分として、エステル系溶媒であるメチルアセテート、エチルアセテート、プロピルアセテート、メチルプロピオネート、γ－ブチロラクトン、γ－バレロラクトン、γ－カプロラクトン、δ－バレロラクトン、ε－カプロラクトン、等が挙げられる。 Other organic solvent components may be contained as long as the non-aqueous electrolytic solution is mainly prepared from the above five kinds of solvents.
Examples of such additive-addable components include 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate, which are cyclic carbonate solvents. -Fluoro-1,3-dioxolane-2-one, trans or cis-4,5-difluoro-1,3-dioxolane-2-one, vinylene carbonate, vinylethylene carbonate, 4-ethynyl-1,3-dioxolane- 2-on, etc. may be mentioned.
In addition, examples of other types of optional components that can be added include chain carbonate-based solvents such as diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, methyl butyl carbonate, and dibutyl carbonate. ..
In addition, as other kinds of optional components that can be added, ester-based solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, and δ-valerolactone, ε-Caprolactone, etc. may be mentioned.

電解質（即ち支持塩）としては、例えばＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＩ等のリチウム化合物（リチウム塩）の１種または２種以上を用いることができる。特に好ましい電解質としてＬｉＰＦ６が挙げられる。なお、電解質の濃度は特に限定されないが、凡そ０．１～５ｍｏｌ／Ｌ（例えば０．５～３ｍｏｌ／Ｌ、典型的には０．８～１．５ｍｏｌ／Ｌ）の濃度とすることができる。
なお、非水電解液二次電池がナトリウムイオン二次電池の場合は、ＮａＰＦ６等のＮａを含む電解質（支持塩）を採用するとよい。 Examples of the electrolyte (that is, supporting salt) include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN (CF 3 SO 2 ) 2 , and LiC (CF 3 SO 2 ). 3. One or more lithium compounds (lithium salts) such as LiI can be used. A particularly preferable electrolyte is LiPF 6 . The concentration of the electrolyte is not particularly limited, but can be approximately 0.1 to 5 mol / L (for example, 0.5 to 3 mol / L, typically 0.8 to 1.5 mol / L). ..
When the non-aqueous electrolyte secondary battery is a sodium ion secondary battery, it is preferable to use an electrolyte (supporting salt) containing Na such as NaPF 6 .

また、非水電解液は、本発明の目的を実現し得る限りにおいて、必要に応じて任意の添加成分を含んでもよい。例えば、電池の出力性能の向上、保存性の向上（保存中における容量低下の抑制等）、サイクル特性の向上、初期充放電効率の向上等の目的で種々の添加剤を含有させることができる。かかる添加剤として、ガス発生剤、皮膜形成剤、分散剤、増粘剤等が挙げられる。そして、上述した各種の非水溶媒および電解質ならびに必要に応じて添加される各種の添加剤を混合することにより、目的とする組成の非水電解液を調製することができる。 Further, the non-aqueous electrolytic solution may contain any additive component, if necessary, as long as the object of the present invention can be realized. For example, various additives can be contained for the purposes of improving the output performance of the battery, improving the storage stability (suppressing the capacity decrease during storage, etc.), improving the cycle characteristics, and improving the initial charge / discharge efficiency. Examples of such additives include gas generators, film-forming agents, dispersants, thickeners and the like. Then, by mixing the various non-aqueous solvents and electrolytes described above and various additives added as needed, a non-aqueous electrolyte solution having a desired composition can be prepared.

上述した各種の材料、部材を用いて図示されるようなリチウムイオン二次電池を製造する。かかる製造方法（即ち、リチウムイオン二次電池を構築する方法）自体は、従来から用いられている手法を適宜採用して行うことができ、本発明を特徴付けるものではないので、ここで詳細な説明は省略する。 A lithium ion secondary battery as shown in the figure is manufactured using the various materials and members described above. Such a manufacturing method (that is, a method for constructing a lithium ion secondary battery) itself can be carried out by appropriately adopting a conventionally used method and does not characterize the present invention, and thus is described in detail here. Is omitted.

ここで開示されるリチウムイオン二次電池は、各種用途に利用可能であるが、極低温域（特に－３０℃以下、例えば－４０℃～－３０℃）における電池性能に優れるため、かかる極低温域における車両駆動用電源等として好適に用いることができる。車両の種類は特に限定されないが、例えばプラグインハイブリッド自動車（ＰＨＶ）、ハイブリッド自動車（ＨＶ）、電気自動車（ＥＶ）、電動アシスト自転車、電動車いす、電気鉄道等が挙げられる。車両に備えられるリチウムイオン二次電池は、通常、複数個が接続された組電池の形態で用いられることは従来と同様であり、組電池の構造等の図示は省略する。 Although the lithium ion secondary battery disclosed here can be used for various purposes, it is excellent in battery performance in an extremely low temperature region (particularly -30 ° C or lower, for example, -40 ° C to -30 ° C), so that the cryogenic temperature is high. It can be suitably used as a power source for driving a vehicle in the region. The type of vehicle is not particularly limited, and examples thereof include a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), an electric vehicle (EV), an electrically assisted bicycle, an electric wheelchair, and an electric railway. The lithium ion secondary battery provided in the vehicle is usually used in the form of an assembled battery in which a plurality of connected batteries are connected, as in the conventional case, and the structure of the assembled battery and the like are not shown.

以下、本発明に関するいくつかの試験例を説明するが、本発明をかかる具体例に示すものに限定することを意図したものではない。 Hereinafter, some test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in such specific examples.

＜非水電解液の調製＞
先ず、電解質としてＬｉＰＦ６を使用し、非水溶媒としてエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）、およびエチルプロピオネート（ＥＰ）を使用し、表１に示す配合比（容積比）で混合することによって計１４種類のリチウムイオン二次電池用非水電解液（例１～例１４）を調製した。ＬｉＰＦ６の濃度はいずれも１．１Ｍとした。各例の非水電解液の大気圧下における凝固点（℃）および引火点温度域（２１℃以上は○、２１℃未満は×で示す）は、表１の該当欄に示すとおりである。 <Preparation of non-aqueous electrolyte solution>
First, LiPF 6 was used as the electrolyte, and ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethyl propionate (EP) were used as non-aqueous solvents. , A total of 14 types of non-aqueous electrolyte solutions for lithium ion secondary batteries (Examples 1 to 14) were prepared by mixing at the compounding ratios (volume ratios) shown in Table 1. The concentration of LiPF 6 was set to 1.1 M in each case. The freezing point (° C.) and the flash point temperature range (indicated by ◯ for 21 ° C. or higher and x for less than 21 ° C.) of the non-aqueous electrolyte solution in each example under atmospheric pressure are as shown in the corresponding columns of Table 1.

Figure 0007032115000001
Figure 0007032115000001

表１に示すように、融点の低いＥＰあるいはＥＭＣの配合比率を高めることにより、非水電解液全体の凝固点を下げることができる。しかしながら、引火点温度域が２１℃未満となってしまい（例７、１３、１４）、安全性の観点から好ましくない配合といえる。
一方、ＰＣおよびＥＰをともに１０ｖｏｌ％配合した例１ならびにＰＣおよびＥＰをともに５ｖｏｌ％配合した例１１では、引火点温度域を２１℃未満に低下させることなく凝固点を－４９℃（例１）または－４４℃（例１１）まで低下させることができ、望ましい配合であることがわかる。
また、詳細なデータは示していないが、０℃以下の低温域においても良好な粘度を示す低粘性の非水電解液として好適である。 As shown in Table 1, the freezing point of the entire non-aqueous electrolytic solution can be lowered by increasing the blending ratio of EP or EMC having a low melting point. However, the flash point temperature range is less than 21 ° C. (Examples 7, 13, 14), which is not preferable from the viewpoint of safety.
On the other hand, in Example 1 in which both PC and EP were blended in 10 vol% and Example 11 in which both PC and EP were blended in 5 vol%, the freezing point was −49 ° C. (Example 1) or in the case where the flash point temperature range was not lowered to less than 21 ° C. The temperature can be lowered to −44 ° C. (Example 11), indicating that the formulation is desirable.
Further, although detailed data are not shown, it is suitable as a low-viscosity non-aqueous electrolytic solution showing good viscosity even in a low temperature range of 0 ° C. or lower.

＜イオン伝導性の評価＞
上記調製した例１～１４の非水電解液のイオン伝導度［ｍＳ／ｃｍ］を測定した。測定は、東洋システム製の密閉二電極セルを使用して、交流インピーダンス法により行った。供試する非水電解液は、ポリテトラフルオロエチレン製のスペーサによって一定の大きさおよび厚さに制御し、これを一対のステンレススチール電極で挟んだ。このセルに１０ｍＶの電圧を印加し、周波数を１ＭＨｚから１０ｍＶへと変化させたときに得られたＣｏｌｅ－Ｃｏｌｅプロットについて、等価回路を用いてカーブフィットすることによりバルク抵抗を求め、イオン伝導度を算出した。
測定温度は、－４０℃、－３０℃および２５℃の３段階とし、各測定温度においてイオン伝導度を測定した。得られた結果を表２に示す。 <Evaluation of ionic conductivity>
The ionic conductivity [mS / cm] of the non-aqueous electrolytic solutions of Examples 1 to 14 prepared above was measured. The measurement was performed by the AC impedance method using a closed two-electrode cell manufactured by Toyo System. The non-aqueous electrolyte solution to be tested was controlled to a constant size and thickness by a spacer made of polytetrafluoroethylene, and this was sandwiched between a pair of stainless steel electrodes. For the Core-Cole plot obtained when a voltage of 10 mV was applied to this cell and the frequency was changed from 1 MHz to 10 mV, the bulk resistance was obtained by curve-fitting using an equivalent circuit, and the ionic conductivity was determined. Calculated.
The measurement temperature was set in three stages of −40 ° C., −30 ° C. and 25 ° C., and the ionic conductivity was measured at each measurement temperature. The results obtained are shown in Table 2.

Figure 0007032115000002
Figure 0007032115000002

表２に示すように、ＰＣおよびＥＰをそれぞれ１０ｖｏｌ％の配合比率で含有する例１の非水電解液は、－３０℃および－４０℃におけるイオン伝導度が相対的に良好であった。同様に、ＰＣおよびＥＰをそれぞれ５ｖｏｌ％の配合比率で含有する例１１の非水電解液もまた－３０℃および－４０℃におけるイオン伝導度が相対的に良好であった。
これに対し、例３、例７および例１３の非水電解液についても－３０℃および－４０℃におけるイオン伝導度が良好であるが、例３については、凝固点が例１と比較して相対的に高めであり、極低温域（例えば－４０℃～－３０℃）の使用において良好とはいえず、例７および例１３については上述のとおり、引火点温度域が２１℃未満であるため好ましくない。 As shown in Table 2, the non-aqueous electrolyte solution of Example 1 containing PC and EP in a blending ratio of 10 vol%, respectively, had relatively good ionic conductivity at −30 ° C. and −40 ° C. Similarly, the non-aqueous electrolyte solution of Example 11 containing PC and EP in a blending ratio of 5 vol%, respectively, also had relatively good ionic conductivity at −30 ° C. and −40 ° C.
On the other hand, the non-aqueous electrolytic solutions of Examples 3, 7 and 13 also have good ionic conductivity at -30 ° C and -40 ° C, but in Example 3, the freezing points are relative to those of Example 1. Because it is relatively high and not good for use in the extremely low temperature range (for example, -40 ° C to -30 ° C), and for Examples 7 and 13, the flash point temperature range is less than 21 ° C as described above. Not preferred.

＜リチウムイオン二次電池の構築＞
正極活物質粉末として、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２（ＬＮＣＭ）を用意した。かかるＬＮＣＭと、導電材としてのアセチレンブラック（ＡＢ）と、バインダとしてのポリフッ化ビニリデン（ＰＶｄＦ）とを、ＬＮＣＭ：ＡＢ：ＰＶｄＦ＝９４：３．５：２．５の質量比となるように混練機に投入し、Ｎ－メチルピロリドン（ＮＭＰ）で粘度を調整しながら混練して、正極活物質層形成用スラリーを調製した。このスラリーを、厚み１２μｍのアルミニウム箔（正極集電体）の両面に塗布し、乾燥後にプレスすることによって、正極集電体上に、密度が約２．９ｇ／ｃｍ３である正極活物質層を有する正極シートを作製した。 <Construction of lithium-ion secondary battery>
LiNi 1/3 Co 1/3 Mn 1/3 O 2 (LNCM) was prepared as the positive electrode active material powder. Such LNCM, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are kneaded so as to have a mass ratio of LNCM: AB: PVdF = 94: 3.5: 2.5. It was put into a machine and kneaded with N-methylpyrrolidone (NMP) while adjusting the viscosity to prepare a slurry for forming a positive electrode active material layer. By applying this slurry to both sides of an aluminum foil (positive electrode current collector) having a thickness of 12 μm and pressing after drying, a positive electrode active material layer having a density of about 2.9 g / cm 3 is applied on the positive electrode current collector. A positive electrode sheet having the above was produced.

負極活物質粉末として非晶質炭素で表面がコートされた球形化天然黒鉛（Ｃ）を用意した。かかる黒鉛（Ｃ）と、バインダとしてのスタジエンブタジエンゴム（ＳＢＲ）と、増粘剤としてのＣＭＣとを、Ｃ：ＳＢＲ：ＣＭＣ＝９９：０．５：０．５の質量比となるように混練機に投入し、イオン交換水で粘度を調整しながら混練して、負極活物質層形成用スラリーを調製した。このスラリーを、厚み８μｍの銅箔（負極集電体）の両面に塗布し、乾燥後にプレスすることによって、負極集電体上に、密度が約１．４ｇ／ｃｍ３である負極活物質層を有する負極シートを作製した。 As the negative electrode active material powder, spherical natural graphite (C) whose surface was coated with amorphous carbon was prepared. The mass ratio of the graphite (C), the stadiene butadiene rubber (SBR) as a binder, and the CMC as a thickener has a mass ratio of C: SBR: CMC = 99: 0.5: 0.5. It was put into a kneader and kneaded while adjusting the viscosity with ion-exchanged water to prepare a slurry for forming a negative electrode active material layer. By applying this slurry to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm and pressing after drying, a negative electrode active material layer having a density of about 1.4 g / cm 3 is applied on the negative electrode current collector. A negative electrode sheet having the above was prepared.

上記で作製した正極シートと負極シートとを、ポリエチレン（ＰＥ）およびポリプロピレン（ＰＰ）からなる３層構造（ＰＰ／ＰＥ／ＰＰ）で厚み２０μｍのセパレータシート２枚とともに捲回し、扁平形状に成形して電極体を作製した。
次に、アルミニウム製の電池ケース蓋体に正極端子および負極端子を取り付け、これらの端子を、捲回電極体端部に露出した正極集電体および負極集電体にそれぞれ溶接した。このようにして蓋体と連結された捲回電極体を、アルミニウム製の電池ケース本体の開口部からその内部に収容し、開口部と蓋体を溶接した。
そして、上記蓋体に設けられた電解液注入孔から、表１に示す例１～例１４のうちの何れかの非水電解液を注入し、当該電解液注入孔を気密に封止した。このようにして、例１～例１４の非水電解液それぞれに対応する例１～例１４の電池組立体を構築した。 The positive electrode sheet and the negative electrode sheet produced above are wound into a flat shape by winding together with two separator sheets having a thickness of 20 μm in a three-layer structure (PP / PE / PP) made of polyethylene (PE) and polypropylene (PP). The electrode body was manufactured.
Next, the positive electrode terminal and the negative electrode terminal were attached to the aluminum battery case lid, and these terminals were welded to the positive electrode current collector and the negative electrode current collector exposed at the end of the wound electrode body, respectively. The wound electrode body connected to the lid body in this way was housed inside from the opening of the battery case body made of aluminum, and the opening and the lid were welded.
Then, a non-aqueous electrolytic solution from any of Examples 1 to 14 shown in Table 1 was injected from the electrolytic solution injection hole provided in the lid, and the electrolytic solution injection hole was hermetically sealed. In this way, the battery assemblies of Examples 1 to 14 corresponding to the non-aqueous electrolytic solutions of Examples 1 to 14 were constructed.

上記作製した例１～例１４に係る電池組立体に対して、コンディショニング処理として、２５℃の温度環境下において、１／３Ｃ（１Ｃは１時間で満充放電可能な電流値）のレートで３時間の定電流（ＣＣ）充電を行い、次いで、１／３Ｃのレートで４．１Ｖまで充電する操作と、１／３Ｃのレートで３．０Ｖまで放電させる操作とを３回繰り返した。
そして、エージング処理として、上記充電処理後の各電池を６０℃の温度環境下（典型的には６０℃に調温した恒温槽内）に２４時間放置した。このようにして、例１～例１４に係る評価試験用リチウムイオン二次電池を構築した。 For the battery assembly according to Examples 1 to 14 produced above, as a conditioning process, 3 at a rate of 1 / 3C (1C is a current value that can be fully charged and discharged in 1 hour) in a temperature environment of 25 ° C. A constant current (CC) charge for a period of time was performed, and then an operation of charging to 4.1 V at a rate of 1 / 3C and an operation of discharging to 3.0 V at a rate of 1 / 3C were repeated three times.
Then, as an aging treatment, each battery after the charging treatment was left in a temperature environment of 60 ° C. (typically in a constant temperature bath adjusted to 60 ° C.) for 24 hours. In this way, the lithium ion secondary batteries for evaluation tests according to Examples 1 to 14 were constructed.

＜初期電池容量の測定＞
例１～例１４に係る評価試験用リチウムイオン二次電池について、上記コンディショニング処理後、２５℃の温度環境下において、３．０Ｖから４．１Ｖの電圧範囲で、以下の手順１～３に従って初期容量を測定した。
（手順１）１／３Ｃの定電流放電によって３．０Ｖに到達後、定電圧放電にて２時間放電し、その後、１０分間休止する。
（手順２）１／３Ｃの定電流充電によって４．１Ｖに到達後、電流が１／１００Ｃとなるまで定電圧充電し、その後、１０分間休止する。
（手順３）１／３Ｃの定電流放電によって、３．０Ｖに到達後、電流が１／１００Ｃとなるまで定電圧放電し、その後、１０分間停止する。
そして、手順３における定電流放電から定電圧放電に至る放電における放電容量（ＣＣＣＶ放電容量）を初期電池容量とした。 <Measurement of initial battery capacity>
For the lithium ion secondary batteries for evaluation test according to Examples 1 to 14, after the above conditioning treatment, in a voltage range of 3.0 V to 4.1 V in a temperature environment of 25 ° C., initial steps 1 to 3 below are followed. The capacity was measured.
(Procedure 1) After reaching 3.0 V by constant current discharge of 1 / 3C, discharge by constant voltage discharge for 2 hours, and then rest for 10 minutes.
(Procedure 2) After reaching 4.1 V by constant current charging of 1 / 3C, constant voltage charging is performed until the current becomes 1 / 100C, and then the device is paused for 10 minutes.
(Procedure 3) After reaching 3.0 V by constant current discharge of 1 / 3C, constant voltage discharge is performed until the current reaches 1 / 100C, and then the process is stopped for 10 minutes.
Then, the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 is defined as the initial battery capacity.

＜ＩＶ抵抗の測定＞
例１～例１４に係るリチウムイオン二次電池のＩＶ抵抗（反応抵抗）を測定した。即ち、各電池を３．０Ｖから１Ｃの定電流で充電し、ＳＯＣ（Ｓｔａｔｅ ｏｆ Ｃｈａｒｇｅ）６０％の充電状態に調整した後、－４０℃、－３０℃又は２５℃の温度環境下において、１０Ｃ（ハイレート放電）で２秒間の定電流（ＣＣ）放電を行い、このときの電流（Ｉ）－電圧（Ｖ）プロット値の一次近似直線の傾きからＩＶ抵抗（ｍΩ）を求めた。結果を表３に示す。 <Measurement of IV resistance>
The IV resistance (reaction resistance) of the lithium ion secondary batteries according to Examples 1 to 14 was measured. That is, each battery is charged with a constant current of 3.0 V to 1 C, adjusted to a charge state of SOC (State of Charge) 60%, and then 10 C in a temperature environment of -40 ° C, -30 ° C, or 25 ° C. A constant current (CC) discharge was performed for 2 seconds at (high rate discharge), and the IV resistance (mΩ) was obtained from the slope of the linear approximation straight line of the current (I) -voltage (V) plot values at this time. The results are shown in Table 3.

＜保存特性の評価＞
上記初期容量を測定した例１～例１４に係るリチウムイオン二次電池について、ＣＣＣＶ方式でＳＯＣが８０％の充電状態に調整した。次いで、各電池を６０℃の恒温槽中に１２０日間保存した後、上記初期電池容量の測定と同様の手法により、各電池の上記保存後の電池容量（保存後電池容量）を測定した。ここで、（保存後電池容量／初期電池容量）×１００の式から１２０日保存後の容量維持率（％）を求め、これを各電池の保存特性の指標として表３に示す。 <Evaluation of storage characteristics>
The lithium ion secondary batteries according to Examples 1 to 14 whose initial capacity was measured were adjusted to a state of charge with an SOC of 80% by the CCCV method. Next, after storing each battery in a constant temperature bath at 60 ° C. for 120 days, the battery capacity after storage (battery capacity after storage) of each battery was measured by the same method as the measurement of the initial battery capacity. Here, the capacity retention rate (%) after 120 days of storage is obtained from the formula (battery capacity after storage / initial battery capacity) × 100, and this is shown in Table 3 as an index of the storage characteristics of each battery.

＜サイクル特性の評価＞
例１～例１４に係るリチウムイオン二次電池について、さらに、サイクル容量維持率（サイクル特性）を測定した。具体的には、２５℃の温度環境下において上記初期電池容量を測定した後、２ＣのＣＣサイクル充放電を１０００サイクル繰り返し、１０００サイクル後の放電容量を測定した。ここで、１０００サイクル後の（放電電池容量／初期電池容量）×１００の式から当該サイクル試験後の容量維持率（％）を求め、これを各電池のサイクル特性の指標として表３に示す。 <Evaluation of cycle characteristics>
For the lithium ion secondary batteries according to Examples 1 to 14, the cycle capacity retention rate (cycle characteristics) was further measured. Specifically, after measuring the initial battery capacity in a temperature environment of 25 ° C., 2C CC cycle charge / discharge was repeated for 1000 cycles, and the discharge capacity after 1000 cycles was measured. Here, the capacity retention rate (%) after the cycle test is obtained from the formula of (discharge battery capacity / initial battery capacity) × 100 after 1000 cycles, and this is shown in Table 3 as an index of the cycle characteristics of each battery.

Figure 0007032115000003
Figure 0007032115000003

表３に示すように、ＰＣおよびＥＰをそれぞれ１０ｖｏｌ％の配合比率で含有する例１の非水電解液を備えるリチウムイオン二次電池ならびにＰＣおよびＥＰをそれぞれ５ｖｏｌ％の配合比率で含有する例１１の非水電解液を備えるリチウムイオン二次電池では、－３０℃および－４０℃におけるＩＶ抵抗値が相対的に低く良好であった。また、６０℃保存特性およびサイクル特性も比較的良好であり、極低温域における電池性能、ならびに耐久性を両立し得る非水電解液二次電池であるといえる。
一方、例３、例７、例９または例１２の非水電解液を備える各リチウムイオン二次電池についても－３０℃および－４０℃におけるＩＶ抵抗値が相対的に低く良好であった。しかし、例３および例１２については、上述のとおり、凝固点が例１や例１１と比較して相対的に高めであり極低温域の使用において良好とはいえない。また、例７については、上述のとおり、引火点温度域が２１℃未満であるため好ましくなく、例９については、凝固点が例１と比較して相対的に高めであることに加えて耐久特性も低く、例１の非水電解液を備えるリチウムイオン二次電池と比べて良好とはいえない。なお、環状カーボネート系溶媒としてＰＣのみを含む例５については、黒鉛表層の剥離を発生させるとともに充放電が困難であり、使用不可であった。 As shown in Table 3, the lithium ion secondary battery provided with the non-aqueous electrolyte solution of Example 1 containing PC and EP in a blending ratio of 10 vol% each, and Example 11 containing PC and EP in a blending ratio of 5 vol% each. In the lithium ion secondary battery equipped with the non-aqueous electrolyte solution, the IV resistance values at −30 ° C. and −40 ° C. were relatively low and good. In addition, it can be said that it is a non-aqueous electrolyte secondary battery that has relatively good storage characteristics at 60 ° C. and cycle characteristics, and can achieve both battery performance and durability in a cryogenic region.
On the other hand, the IV resistance values at −30 ° C. and −40 ° C. were relatively low and good for each lithium ion secondary battery provided with the non-aqueous electrolytic solution of Example 3, Example 7, Example 9, or Example 12. However, in Examples 3 and 12, as described above, the freezing point is relatively high as compared with Examples 1 and 11, and it cannot be said that it is good for use in the cryogenic region. Further, as described above, Example 7 is not preferable because the flash point temperature range is less than 21 ° C., and Example 9 has a relatively high freezing point as compared with Example 1 and has durability characteristics. It is also low, and it cannot be said that it is better than the lithium ion secondary battery provided with the non-aqueous electrolytic solution of Example 1. In Example 5, which contained only PC as the cyclic carbonate solvent, the graphite surface layer was peeled off and charging / discharging was difficult, so that it could not be used.

２０ 捲回電極体
３０ 電池ケース
３２ 電池ケース本体
３４ 蓋体
３６ 安全弁
４２ 正極端子
４２ａ 正極集電板
４４ 負極端子
４４ａ 負極集電板
５０ 正極（正極シート）
５２ 正極集電体
５２ａ 正極活物質層非形成部
５４ 正極活物質層
６０ 負極（負極シート）
６２ 負極集電体
６２ａ 負極活物質層非形成部
６４ 負極活物質層
７０ セパレータ
１００ リチウムイオン二次電池 20 Winding electrode body 30 Battery case 32 Battery case body 34 Lid body 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode (positive electrode sheet)
52 Positive electrode current collector 52a Positive electrode active material layer non-forming portion 54 Positive electrode active material layer 60 Negative electrode (negative electrode sheet)
62 Negative electrode current collector 62a Negative electrode active material layer non-forming portion 64 Negative electrode active material layer 70 Separator 100 Lithium ion secondary battery

Claims (4)

正極、負極、および非水溶媒と電解質とを含む非水電解液を備えた非水電解液二次電池であって、
前記負極は、少なくとも負極活物質を含む負極活物質層を備え、
前記負極活物質は、黒鉛の表面に非晶質炭素を備えた非晶質コート黒鉛系材料であり、
前記非水溶媒は、
環状カーボネート系溶媒として少なくともエチレンカーボネート（ＥＣ）およびプロピレンカーボネート（ＰＣ）を含み、
鎖状カーボネート系溶媒として少なくともジメチルカーボネート（ＤＭＣ）およびエチルメチルカーボネート（ＥＭＣ）を含み、
さらにエステル系溶媒として少なくともエチルプロピオネート（ＥＰ）を含み、
ここで前記非水溶媒全体を１００ｖｏｌ％としたときのそれぞれの含有率が
ＥＣ ２０～３０ｖｏｌ％；
ＰＣ ５～１０ｖｏｌ％ ；
ＥＰ ５～１０ｖｏｌ％ ；
ＤＭＣ＋ＥＭＣ ５０～７０ｖｏｌ％；
である、非水電解液二次電池。 A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte.
The negative electrode comprises a negative electrode active material layer containing at least the negative electrode active material.
The negative electrode active material is an amorphous coated graphite-based material having amorphous carbon on the surface of graphite.
The non-aqueous solvent is
It contains at least ethylene carbonate (EC) and propylene carbonate (PC) as the cyclic carbonate solvent, and contains at least ethylene carbonate (EC) and propylene carbonate (PC).
It contains at least dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as a chain carbonate solvent.
Further, it contains at least ethyl propionate (EP) as an ester solvent, and contains
Here, when the total content of the non-aqueous solvent is 100 vol%, the respective contents are EC 20 to 30 vol%;
PC 5-10 vol%;
EP 5-10 vol%;
DMC + EMC 50-70 vol%;
A non-aqueous electrolyte secondary battery. 前記ジメチルカーボネート（ＤＭＣ）の含有率および前記エチルメチルカーボネート（ＥＭＣ）の含有率は、いずれも２５～３５ｖｏｌ％である、請求項１に記載の非水電解液二次電池。 The non-aqueous electrolytic solution secondary battery according to claim 1, wherein the content of the dimethyl carbonate (DMC) and the content of the ethylmethyl carbonate (EMC) are both 25 to 35 vol%. 前記非水電解液の凝固点が－４０℃未満である、請求項１または２に記載の非水電解液二次電池。 The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte has a freezing point of less than −40 ° C. 前記非水電解液の－４０℃におけるイオン伝導度（ｍＳ／ｃｍ）が１．０以上である、請求項１～３のいずれか一項に記載の非水電解液二次電池。 The non-aqueous electrolytic solution secondary battery according to any one of claims 1 to 3, wherein the non-aqueous electrolytic solution has an ionic conductivity (mS / cm) of 1.0 or more at −40 ° C.
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