JP2016152071A - Secondary battery - Google Patents

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JP2016152071A
JP2016152071A JP2015027538A JP2015027538A JP2016152071A JP 2016152071 A JP2016152071 A JP 2016152071A JP 2015027538 A JP2015027538 A JP 2015027538A JP 2015027538 A JP2015027538 A JP 2015027538A JP 2016152071 A JP2016152071 A JP 2016152071A
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battery
positive electrode
secondary battery
separator
temperature
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真登 向山
Masato Mukoyama
真登 向山
康資 岩瀬
Kosuke Iwase
康資 岩瀬
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Toyota Motor Corp
Soken Inc
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Nippon Soken Inc
Toyota Motor Corp
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    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having both of an excellent battery characteristic under a low temperature environment and high reliability under overcharging.SOLUTION: A secondary battery 50 comprises an electrode body 10 which is configured so that a positive electrode and a negative electrode are stacked through a separator and then wound around an axial core 12, and electrolytic solution. The separator has a shutdown function. The axial core 12 has a metal material which develops an endothermal reaction in a temperature area which is not less than the shutdown temperature of the separator and lower than the thermal decomposition temperature of the positive electrode. The surface of the axial core 12 is coated with resin material having lower thermal conductivity than the metal material.SELECTED DRAWING: Figure 1

Description

本発明は、二次電池に関する。詳しくは、捲回電極体を備えた二次電池に関する。   The present invention relates to a secondary battery. Specifically, the present invention relates to a secondary battery including a wound electrode body.

二次電池は、誤操作等によって所定以上の電流が供給されると、通常使用時の電圧を超えて過充電となることがある。過充電が進行すると活物質（典型的には正極活物質）の発熱や電解液の分解等が顕著となる。これにより、電池内部の温度が過度に上昇して、電池自体に不具合（例えば熱暴走）を生じることがあり得る。
過充電の進行を停止する安全機構の一例としては、いわゆるシャットダウン機能を備えたセパレータが知られている。かかるセパレータでは、電池内部の温度が所定温度まで上昇すると構成材料が軟化（溶融）あるいは熱収縮して、微細孔が閉塞する。これにより、正負極間の電荷担体の移動を遮断して充放電反応を停止させる。 If a current exceeding a predetermined level is supplied due to an erroneous operation or the like, the secondary battery may exceed the voltage during normal use and be overcharged. As overcharge proceeds, heat generation of the active material (typically, the positive electrode active material), decomposition of the electrolyte, and the like become significant. Thereby, the temperature inside a battery rises too much and a malfunction (for example, thermal runaway) may arise in battery itself.
As an example of a safety mechanism for stopping the progress of overcharge, a separator having a so-called shutdown function is known. In such a separator, when the temperature inside the battery rises to a predetermined temperature, the constituent material is softened (melted) or thermally contracted, and the micropores are closed. Thereby, the movement of the charge carrier between the positive and negative electrodes is blocked to stop the charge / discharge reaction.

また、過充電時に電池内部の温度上昇を抑制する従来技術の一例として、特許文献１〜４が挙げられる。例えば特許文献１には、捲回電極体の中心に熱伝導性の高い材料（例えば銅）からなる軸芯を備え、当該軸芯が放熱板等を介して電池ケースと接するよう配置されたリチウムイオン二次電池が記載されている。特許文献１の構成によれば、軸芯を通じて電池内部の熱を電池ケースに逃がすことができる。これにより、過充電時の放熱性を高めて、電池自体に熱暴走等の不具合が生じることを回避し得る。   Moreover, patent documents 1-4 are mentioned as an example of the prior art which suppresses the temperature rise inside a battery at the time of overcharge. For example, Patent Document 1 discloses a lithium electrode that includes an axial core made of a material having high thermal conductivity (for example, copper) at the center of a wound electrode body, and the axial core is disposed so as to be in contact with a battery case via a heat sink or the like. An ion secondary battery is described. According to the configuration of Patent Document 1, heat inside the battery can be released to the battery case through the shaft core. Thereby, the heat dissipation at the time of overcharge can be improved, and it can avoid that malfunctions, such as thermal runaway, arise in battery itself.

特開２０１１―１１３８９５号公報JP 2011-113895 A 特開平１１−０４０２００号公報Japanese Patent Laid-Open No. 11-040200 特開２０１２−０６４５０１号公報JP 2012-064501 A 特開平１０−０９２４６９号公報Japanese Patent Laid-Open No. 10-092469

しかしながら、特許文献１の技術を例えば０℃以下の低温環境下で使用され得る二次電池に適用する場合、未だ改善の余地が認められた。つまり、特許文献１に記載される二次電池は捲回電極体の中心に熱伝導性の高い軸芯を有する。このため、通常使用時にあっても放熱性が高く、電池内部が暖まりにくい傾向がある。一般に、二次電池では使用環境の温度が低いほど電荷担体のイオン伝導性が低下して抵抗が高くなる。その結果、特許文献１の二次電池では、例えば上記軸芯を有しない二次電池に比べて低温環境下の電池特性（例えば充放電効率）が低下したり、本来の性能が発揮されるまでに時間を要したりすることがある。換言すれば、特許文献１の二次電池では、通常使用時に電池内部の温度上昇に伴うポジティブな効果を得難い背反がある。上記のように、低温環境下で使用され得る二次電池では、過充電時の信頼性と通常使用時の電池特性との両立を考慮する必要がある。   However, when the technique of Patent Document 1 is applied to a secondary battery that can be used in a low temperature environment of, for example, 0 ° C. or less, there is still room for improvement. That is, the secondary battery described in Patent Document 1 has an axial core with high thermal conductivity at the center of the wound electrode body. For this reason, even during normal use, the heat dissipation is high and the inside of the battery tends not to warm up. Generally, in a secondary battery, the lower the temperature of the use environment, the lower the ion conductivity of the charge carrier and the higher the resistance. As a result, in the secondary battery of Patent Document 1, for example, battery characteristics (for example, charge / discharge efficiency) in a low-temperature environment are deteriorated or the original performance is exhibited as compared with the secondary battery having no shaft core. May take time. In other words, the secondary battery of Patent Document 1 has a tradeoff that makes it difficult to obtain a positive effect associated with a temperature rise inside the battery during normal use. As described above, in a secondary battery that can be used in a low-temperature environment, it is necessary to consider both the reliability during overcharging and the battery characteristics during normal use.

本発明は、かかる事情に鑑みてなされたものであり、その目的は、捲回電極体を備える二次電池であって、低温環境下での優れた電池特性と過充電時の高い信頼性とを兼ね備えた二次電池を提供することにある。   The present invention has been made in view of such circumstances, and an object thereof is a secondary battery including a wound electrode body, which has excellent battery characteristics in a low temperature environment and high reliability during overcharge. It is in providing the secondary battery which combines.

本発明者らは、通常使用時の（特には低温環境下における）放熱性を抑制する一方で、電池内部の温度が過度に上昇した場合に限って放熱性を発揮させ、電池内部の温度上昇を抑制しようと考えた。そして、上記目的を実現すべく様々な角度から鋭意検討を重ね、本発明を完成させた。
本発明により、正極および負極がセパレータを介して重ね合わされ軸芯の周りに捲回された構造の電極体と、電解液と、を備える二次電池が提供される。上記セパレータは、シャットダウン機能を有する。上記軸芯は、上記セパレータのシャットダウン温度以上であって上記正極の熱分解温度よりも低い温度域で吸熱反応を生じる金属材料を有する。上記軸芯の表面は上記金属材料よりも熱伝導性が低い樹脂材料によってコートされている。 While suppressing the heat dissipation during normal use (especially in a low temperature environment), the present inventors exert heat dissipation only when the temperature inside the battery rises excessively, increasing the temperature inside the battery. Thought to suppress. The present invention has been completed by intensive studies from various angles to achieve the above object.
According to the present invention, there is provided a secondary battery comprising an electrode body having a structure in which a positive electrode and a negative electrode are superimposed with a separator interposed therebetween and wound around an axis, and an electrolytic solution. The separator has a shutdown function. The shaft core includes a metal material that generates an endothermic reaction in a temperature range that is equal to or higher than the shutdown temperature of the separator and lower than the thermal decomposition temperature of the positive electrode. The surface of the shaft core is coated with a resin material having lower thermal conductivity than the metal material.

ここに開示される二次電池の捲回電極体では、電池内部の温度が所定の温度に達すると、軸芯を構成する金属材料が吸熱反応（典型的には相転移）する。この効果により、電池内部の温度が過度に上昇することを防ぎ、過充電時には電池自体に不具合（例えば熱暴走）が生じることを高度に防止することができる。また、ここに開示される二次電池の捲回電極体では、軸芯の表面が熱伝導性の低い樹脂材料でコートされている。この効果により、通常の電池使用時には（例えば８０℃以下の温度域では）軸芯の熱伝導性が低く抑えられている。したがって、電池内部の温度上昇に伴うポジティブな効果を享受することができ、特に低温環境下において優れた電池特性を発揮することができる。   In the wound electrode body of the secondary battery disclosed herein, when the temperature inside the battery reaches a predetermined temperature, the metal material constituting the shaft core undergoes an endothermic reaction (typically a phase transition). By this effect, it is possible to prevent the temperature inside the battery from rising excessively, and to highly prevent the malfunction of the battery itself (for example, thermal runaway) during overcharging. Further, in the wound electrode body of the secondary battery disclosed herein, the surface of the shaft core is coated with a resin material having low thermal conductivity. Due to this effect, the thermal conductivity of the shaft core is kept low when a normal battery is used (for example, in a temperature range of 80 ° C. or lower). Therefore, the positive effect accompanying the temperature rise inside the battery can be enjoyed, and excellent battery characteristics can be exhibited particularly in a low temperature environment.

本発明の一実施形態に係る二次電池の内部構成を示す模式図であり、（ａ）は縦断面図を、（ｂ）は（ａ）のIｂ−Iｂ線に沿った部分断面図を示している。It is a schematic diagram which shows the internal structure of the secondary battery which concerns on one Embodiment of this invention, (a) shows a longitudinal cross-sectional view, (b) shows the fragmentary sectional view along the Ib-Ib line | wire of (a). ing. 比較例２に係る二次電池の内部構成を示す模式図であり、（ａ）は縦断面図を、（ｂ）は（ａ）のIIｂ−IIｂ線に沿った部分断面図を示している。It is a schematic diagram which shows the internal structure of the secondary battery which concerns on the comparative example 2, (a) is a longitudinal cross-sectional view, (b) has shown the fragmentary sectional view along the IIb-IIb line | wire of (a). 過充電試験時の挙動を示すグラフであり、（ａ）は電圧の経時変化を、（ｂ）は電池ケースの温度の経時変化を示している。It is a graph which shows the behavior at the time of an overcharge test, (a) shows the time-dependent change of a voltage, (b) has shown the time-dependent change of the temperature of a battery case. 低温環境下でパルス放電試験を行った際の、電圧の経時変化を示すグラフである。It is a graph which shows a time-dependent change of a voltage at the time of performing a pulse discharge test in a low temperature environment.

以下、適宜図面を参照しつつ、本発明の一実施形態を説明する。なお、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本発明の実施に必要な事柄（例えば、本発明を特徴付けない構成要素や電池の一般的な電池構築プロセス）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。また、以下の図面において、同じ作用を奏する部材・部位には同じ符号を付し、重複する説明は省略または簡略化することがある。各図における寸法関係（長さ、幅、厚さ等）は必ずしも実際の寸法関係を反映するものではない。   Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. Note that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention (for example, a general battery construction process of components and batteries that do not characterize the present invention) It can be grasped as a design matter of a person skilled in the art based on the prior art in the 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 | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not necessarily reflect the actual dimensional relationship.

ここに開示される二次電池は、捲回電極体と電解液とを備える。
特に限定することを意図したものではないが、以下では本発明の一実施形態に係る二次電池の構成を例に説明する。
図１は、本発明の一実施形態に係る二次電池の内部構成を示す模式図である。図１（ａ）は縦断面図である。図１（ｂ）はIｂ−Iｂ線に沿った部分断面図である。図１（ａ）に示す二次電池５０は、捲回電極体１０と図示しない電解液とが電池ケース２０に封入され、封止された構造である。 The secondary battery disclosed herein includes a wound electrode body and an electrolytic solution.
Although not intended to be particularly limited, a configuration of a secondary battery according to an embodiment of the present invention will be described below as an example.
FIG. 1 is a schematic diagram showing an internal configuration of a secondary battery according to an embodiment of the present invention. FIG. 1A is a longitudinal sectional view. FIG. 1B is a partial cross-sectional view taken along line Ib-Ib. A secondary battery 50 shown in FIG. 1A has a structure in which a wound electrode body 10 and an electrolyte solution (not shown) are enclosed in a battery case 20 and sealed.

捲回電極体１０は、正極および負極がセパレータを介して重ね合わされ（積層され）、軸芯１２の周りに捲回された構造である。典型的には、長尺状の正極シートおよび長尺状の負極シートが長尺状のセパレータシートを介して重ね合わされ、軸芯１２の周りに長尺方向に捲回された構造である。ここに示す態様では、軸芯１２ならびに捲回電極体１０全体の外観が扁平形状である。換言すれば、図１（ｂ）に示すように、捲回軸と直交する断面において、軸芯１２ならびに捲回電極体１０の外観が略角丸長方形状である。   The wound electrode body 10 has a structure in which a positive electrode and a negative electrode are overlapped (stacked) via a separator and wound around an axis 12. Typically, a long positive electrode sheet and a long negative electrode sheet are superposed via a long separator sheet and wound around the shaft core 12 in the long direction. In the aspect shown here, the external appearance of the shaft core 12 and the wound electrode body 10 as a whole is flat. In other words, as shown in FIG. 1B, the outer appearance of the shaft core 12 and the wound electrode body 10 are substantially rounded rectangular in the cross section orthogonal to the wound axis.

正極は、典型的には、長尺状の正極集電体と、その表面に形成された正極活物質層とを備える。正極集電体としては、導電性の良好な金属（例えばアルミニウム、ニッケル等）からなる導電性部材が好適である。正極活物質層は、典型的には、正極集電体の表面に長尺方向に沿って所定の幅で（帯状に）形成されている。また、正極集電体の長手方向に直交する幅方向の一方の端部は、長手方向に沿って正極活物質層が形成されていない正極活物質層非形成部分１４を構成している。   The positive electrode typically includes a long positive electrode current collector and a positive electrode active material layer formed on the surface thereof. As the positive electrode current collector, a conductive member made of a highly conductive metal (for example, aluminum, nickel, etc.) is suitable. The positive electrode active material layer is typically formed on the surface of the positive electrode current collector with a predetermined width (in a strip shape) along the longitudinal direction. Further, one end in the width direction orthogonal to the longitudinal direction of the positive electrode current collector constitutes a positive electrode active material layer non-formed portion 14 in which the positive electrode active material layer is not formed along the longitudinal direction.

正極活物質層は、少なくとも正極活物質を含む。正極活物質としては、例えば、ＬｉＮｉＯ２、ＬｉＣｏＯ２、ＬｉＦｅＯ２、ＬｉＭｎ２Ｏ４、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ０．５Ｍｎ１．５Ｏ４等のリチウム遷移金属複合酸化物が好適である。正極活物質層は、正極活物質に加えて導電材やバインダ等を含み得る。導電材としては、例えば、カーボンブラック（例えば、アセチレンブラックやケッチェンブラック）、活性炭、黒鉛等の炭素材料が例示される。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や、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が例示される。 The positive electrode active material layer includes at least a positive electrode active material. Examples of the positive electrode active material include lithium such as LiNiO 2 , LiCoO 2 , LiFeO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , and LiNi 0.5 Mn 1.5 O 4. Transition metal composite oxides are preferred. The positive electrode active material layer can include a conductive material, a binder, and the like in addition to the positive electrode active material. Examples of the conductive material include carbon materials such as carbon black (for example, acetylene black and ketjen black), activated carbon, and graphite. Examples of the binder include vinyl halide resins such as polyvinylidene fluoride (PVdF) and polyalkylene oxides such as polyethylene oxide (PEO).

なお、上記正極活物質を含む正極は、高ＳＯＣ状態（例えばＳＯＣ８０％以上の状態）において、熱分解温度（発熱温度）が概ね２３０℃以上であり得る。正極の熱分解温度は、例えば以下のような手順で把握し得る。まず二次電池を解体して正極活物質層を採取し、ＤＳＣ（示差走査熱量計）で分析する。そして、得られたチャート（温度−熱量）から、例えば発熱量の大きい発熱ピークの温度を読み取る。なお、かかる発熱ピークは、例えば正極活物質の結晶構造の変化や酸素脱離、あるいは電解液の酸化分解等に由来するものであり得る。   The positive electrode including the positive electrode active material may have a thermal decomposition temperature (exothermic temperature) of approximately 230 ° C. or higher in a high SOC state (for example, a state where the SOC is 80% or higher). The thermal decomposition temperature of the positive electrode can be grasped by the following procedure, for example. First, the secondary battery is disassembled, the positive electrode active material layer is collected, and analyzed by DSC (differential scanning calorimeter). Then, for example, the temperature of a heat generation peak having a large heat generation amount is read from the obtained chart (temperature-heat amount). Such an exothermic peak can be derived from, for example, a change in the crystal structure of the positive electrode active material, oxygen desorption, or oxidative decomposition of the electrolyte.

負極は、典型的には、長尺状の負極集電体と、その表面に形成された負極活物質層とを備える。負極集電体としては、導電性の良好な金属（例えば、銅、ニッケル等）からなる導電性材料が好適である。負極活物質層は、典型的には、負極集電体の表面に、長尺方向に沿って正極活物質層よりも広い幅で（帯状に）形成されている。また、負極集電体の長手方向に直交する幅方向の一方の端部は、長手方向に沿って負極活物質層が形成されていない負極活物質層非形成部分１６を構成している。   The negative electrode typically includes a long negative electrode current collector and a negative electrode active material layer formed on the surface thereof. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, etc.) is suitable. The negative electrode active material layer is typically formed on the surface of the negative electrode current collector with a width (in a strip shape) wider than the positive electrode active material layer along the longitudinal direction. Also, one end in the width direction orthogonal to the longitudinal direction of the negative electrode current collector constitutes a negative electrode active material layer non-formed portion 16 in which the negative electrode active material layer is not formed along the longitudinal direction.

負極活物質層は、少なくとも負極活物質を含む。負極活物質としては、天然黒鉛、人造黒鉛、非晶質コート黒鉛（黒鉛粒子の表面に非晶質カーボンをコートした形態のもの）等の黒鉛系炭素材料が好適である。負極活物質層は、負極活物質に加えて増粘剤やバインダ等を含み得る。増粘剤としては、例えば、カルボキシメチルセルロース（ＣＭＣ）やメチルセルロース（ＭＣ）等のセルロース類が例示される。バインダとしては、例えば、スチレンブタジエンゴム（ＳＢＲ）等のゴム類や、ポリフッ化ビニリデン（ＰＶｄＦ）等のハロゲン化ビニル樹脂が例示される。   The negative electrode active material layer includes at least a negative electrode active material. As the negative electrode active material, graphite-based carbon materials such as natural graphite, artificial graphite, and amorphous-coated graphite (forms in which amorphous carbon is coated on the surface of graphite particles) are suitable. The negative electrode active material layer can contain a thickener, a binder, and the like in addition to the negative electrode active material. Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC) and methyl cellulose (MC). Examples of the binder include rubbers such as styrene butadiene rubber (SBR) and vinyl halide resins such as polyvinylidene fluoride (PVdF).

正極と負極の間に配されるセパレータとしては、シャットダウン機能を有するものであればよい。例えば、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、ポリイミド等の樹脂から成る多孔質樹脂シート（フィルム）が例示される。例えばＰＥやＰＰ等に代表されるポリオレフィン系の樹脂は、ＤＳＣに基づく融点が電池の通常使用時の温度域よりも高い。具体的には、融点が、典型的には１００℃以上、例えば１１０℃以上、敢えて言えば１２０℃以上であって、１７０℃以下、例えば１５０℃以下、好ましくは１４０℃以下であり得る。このため、ポリオレフィン系の樹脂を含むセパレータでは、シャットダウン温度をより低い温度域内に設定することができる。その結果、電池内部の温度が過度に上昇する前に（過充電の初期段階で）、正負極間の電流を遮断することができる。したがって、信頼性向上の観点から好ましい。   As a separator disposed between the positive electrode and the negative electrode, any separator having a shutdown function may be used. For example, a porous resin sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, or polyimide is exemplified. For example, polyolefin resins typified by PE and PP have a melting point based on DSC higher than the temperature range during normal use of the battery. Specifically, the melting point is typically 100 ° C. or higher, such as 110 ° C. or higher, dare to say 120 ° C. or higher, and may be 170 ° C. or lower, such as 150 ° C. or lower, preferably 140 ° C. or lower. For this reason, in the separator containing polyolefin resin, the shutdown temperature can be set in a lower temperature range. As a result, the current between the positive and negative electrodes can be cut off before the temperature inside the battery rises excessively (at the initial stage of overcharging). Therefore, it is preferable from the viewpoint of improving reliability.

ここに開示される技術において、軸芯１２は所定の温度域で吸熱反応を生じる金属材料を含む。また、軸芯１２の表面は上記金属材料よりも熱伝導性が低い樹脂材料でコートされている。換言すれば、軸芯１２は、例えば、（１）所定の温度域で吸熱反応を生じる金属材料からなる芯部と、（２）上記芯部の表面に形成された樹脂材料からなるコート部と、の二層構造であり得る。また、上記（１）と（２）の間に他の中間層を備え得る。   In the technique disclosed herein, the shaft core 12 includes a metal material that generates an endothermic reaction in a predetermined temperature range. The surface of the shaft core 12 is coated with a resin material having a lower thermal conductivity than the metal material. In other words, the shaft core 12 includes, for example, (1) a core portion made of a metal material that generates an endothermic reaction in a predetermined temperature range, and (2) a coat portion made of a resin material formed on the surface of the core portion. , A two-layer structure. Moreover, another intermediate | middle layer can be provided between said (1) and (2).

軸芯１２に含まれる金属材料としては、上記セパレータのシャットダウン温度以上であって上記正極の熱分解温度よりも低い温度域で吸熱反応を生じるものであればよい。一好適例として、融点が、上記セパレータのシャットダウン温度以上、典型的には１００℃以上、例えば１１０℃以上、敢えて言えば１２０℃以上であって、かつ、上記正極の熱分解温度よりも低く、典型的には２３０℃以下、例えば２３０℃未満、好ましくは２００℃以下、より好ましくは１５０℃以下、特には１４０℃以下の温度域にある低融点金属材料が挙げられる。かかる低融点金属材料は、上記温度域において固体から液体へと相転移する。この相転移は吸熱の物理反応である。したがって、セパレータのシャットダウン後に電池内部の温度を迅速かつ効果的に低下させることができる。その結果、熱暴走等の不具合を的確に防止することができ、電池の信頼性（過充電耐性）を向上することができる。低融点金属材料の一例としては、インジウム（Ｉｎ）、スズ（Ｓｎ）、ビスマス（Ｂｉ）、亜鉛（Ｚｎ）、鉛（Ｐｂ）等を主成分とする低融点合金（易融合金）が挙げられる。より具体的には、例えば、Ｓｎ−Ｂｉ、Ｓｎ−Ｉｎ、Ｓｎ-Ｐｂ、Ｓｎ-Ｚｎの二元合金が例示される。   The metal material included in the shaft core 12 may be any metal material that generates an endothermic reaction in a temperature range that is equal to or higher than the shutdown temperature of the separator and lower than the thermal decomposition temperature of the positive electrode. As a preferred example, the melting point is not less than the shutdown temperature of the separator, typically not less than 100 ° C., such as not less than 110 ° C., for example, not less than 120 ° C., and lower than the thermal decomposition temperature of the positive electrode, Typically, a low-melting-point metal material having a temperature range of 230 ° C. or lower, for example, less than 230 ° C., preferably 200 ° C. or lower, more preferably 150 ° C. or lower, and particularly 140 ° C. or lower is given. Such a low-melting-point metal material undergoes a phase transition from a solid to a liquid in the temperature range. This phase transition is an endothermic physical reaction. Therefore, the temperature inside the battery can be quickly and effectively lowered after the shutdown of the separator. As a result, problems such as thermal runaway can be prevented accurately, and the battery reliability (overcharge resistance) can be improved. As an example of the low melting point metal material, a low melting point alloy (easy fusion gold) whose main component is indium (In), tin (Sn), bismuth (Bi), zinc (Zn), lead (Pb), or the like can be given. . More specifically, for example, a binary alloy of Sn—Bi, Sn—In, Sn—Pb, and Sn—Zn is exemplified.

軸芯１２の表面をコートする樹脂材料としては、上記金属材料よりも熱伝導性が低いものであればよい。一好適例として、ホットディスク法に基づく熱伝導率が０．３Ｗ／ｍ・Ｋ以下の樹脂材料が挙げられる。より好ましくは、電池の通常使用時の温度域（例えば、−４０℃〜＋８０℃）において、膨張・収縮等が生じ難く、熱安定性に優れる材料がよい。さらには軸芯１２に含まれる金属材料と親和性の高い材料がよい。このような熱伝導率や熱安定性、金属材料との親和性を示し得る樹脂材料の一例として、上記セパレータの構成材料として上述したものが挙げられる。なかでもポリイミドが好適である。なお、ここで「ポリイミド」とは、主鎖の繰り返し単位にイミド結合を含むポリマー全般をいう。   The resin material that coats the surface of the shaft core 12 may be any material that has lower thermal conductivity than the metal material. As a preferred example, a resin material having a thermal conductivity of 0.3 W / m · K or less based on a hot disk method can be given. More preferably, a material that hardly expands and contracts and has excellent thermal stability in a temperature range (for example, −40 ° C. to + 80 ° C.) during normal use of the battery is preferable. Furthermore, a material having high affinity with the metal material included in the shaft core 12 is preferable. As an example of a resin material that can exhibit such thermal conductivity, thermal stability, and affinity with a metal material, those described above as the constituent material of the separator can be given. Of these, polyimide is preferred. Here, “polyimide” refers to all polymers containing an imide bond in the repeating unit of the main chain.

電池の通常使用時において、軸芯１２の表面は、実質的に（例えば全表面積の９５％以上が）上記樹脂材料によって被覆されている。換言すれば、軸芯１２に含まれる金属材料と、他の構成部材（例えば正負極や電解液）との間に、熱伝導率の低い樹脂材料が介在している。つまり、金属材料と他の構成部材との直接的な接触が回避されている。その結果、通常使用時にあっては、電池内部の放熱性が抑制される。したがって、例えば０℃以下の低温環境下において、イオン伝導性の低下が抑えられる。これにより、例えば特許文献１に記載される従来技術に比べて、優れた低温特性を実現することができる。   During normal use of the battery, the surface of the shaft core 12 is substantially covered with the resin material (for example, 95% or more of the total surface area). In other words, a resin material having low thermal conductivity is interposed between the metal material included in the shaft core 12 and other constituent members (for example, positive and negative electrodes and electrolyte). That is, direct contact between the metal material and the other constituent members is avoided. As a result, the heat dissipation within the battery is suppressed during normal use. Therefore, for example, a decrease in ionic conductivity can be suppressed in a low temperature environment of 0 ° C. or lower. Thereby, compared with the prior art described, for example in patent document 1, the outstanding low temperature characteristic is realizable.

電解液は、典型的には溶媒と支持塩とを含む。溶媒としては、例えば、カーボネート類、エステル類、エーテル類、ニトリル類、スルホン類、ラクトン類等の非水溶媒が例示される。なかでも、エチレンカーボネート（ＥＣ）、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）等のカーボネート類が好適である。支持塩としては、リチウム塩、ナトリウム塩、マグネシウム塩等が例示される。なかでも、ＬｉＰＦ６、ＬｉＢＦ４等のリチウム塩が好適である。 The electrolytic solution typically includes a solvent and a supporting salt. Examples of the solvent include nonaqueous solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are preferable. Examples of the supporting salt include lithium salt, sodium salt, magnesium salt and the like. Of these, lithium salts such as LiPF 6 and LiBF 4 are preferable.

電池ケース２０は、上端が開放された扁平な直方体形状（角形）の電池ケース本体２２と、その開口部を塞ぐ蓋板２４とを備える。電池ケース２０の上面（すなわち蓋板２４）には、外部接続用の正極端子２６および負極端子２８が設けられている。図１（ａ）に示す態様では、捲回電極体１０の正極活物質層非形成部分１４および負極活物質層非形成部分１６に、正極集電板１５および負極集電板１７がそれぞれ付設されており、これら集電板が正極端子２６および負極端子２８と電気的に接続されている。   The battery case 20 includes a flat rectangular parallelepiped (square) battery case main body 22 having an open upper end, and a lid plate 24 that closes the opening. A positive electrode terminal 26 and a negative electrode terminal 28 for external connection are provided on the upper surface of the battery case 20 (that is, the cover plate 24). In the embodiment shown in FIG. 1 (a), a positive electrode current collector plate 15 and a negative electrode current collector plate 17 are attached to the positive electrode active material layer non-formed part 14 and the negative electrode active material layer non-formed part 16 of the wound electrode body 10, respectively. These current collecting plates are electrically connected to the positive terminal 26 and the negative terminal 28.

ここで開示される二次電池は各種用途に利用可能であるが、捲回電極体を備えることで高エネルギー密度や高容量を実現し得る。また、捲回電極体が上記要件を具備することで、従来品に比べて、通常使用時の電池特性（特には低温特性）と過充電時の高い信頼性とを高いレベルで両立可能なことを特徴とする。したがって、かかる特徴を活かして、例えば、プラグインハイブリッド自動車、ハイブリッド自動車、電気自動車等に搭載される車両駆動用電源として好適に利用し得る。   Although the secondary battery disclosed here can be used for various applications, a high energy density and a high capacity can be realized by providing a wound electrode body. In addition, because the wound electrode body has the above requirements, battery characteristics during normal use (especially low temperature characteristics) and high reliability during overcharge can be achieved at a higher level than conventional products. It is characterized by. Therefore, taking advantage of such characteristics, for example, it can be suitably used as a power source for driving a vehicle mounted on a plug-in hybrid vehicle, a hybrid vehicle, an electric vehicle, or the like.

以下、本発明に関するいくつかの実施例を説明するが、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。   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.

本試験例では、捲回電極体の軸芯部分のみが異なる３つの二次電池（実施例、比較例１，２）を構築し、過充電時の挙動と、低温環境下での電池特性を確認した。
≪実施例≫
実施例に係る二次電池の構築にあたって、以下の電池構成部材を用意した。
〔捲回電極体構築用〕
・正極；長尺状のアルミ箔（正極集電体）の両面に、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２（正極活物質）とアセチレンブラック（導電材）とポリフッ化ビニリデン（バインダ）とを質量比９０：８：２で含む帯状の正極活物質層を備えた正極シート。
・負極；長尺状の銅箔（負極集電体）の両面に、黒鉛（負極活物質）とカルボキシメチルセルロース（増粘剤）とスチレンブタジエンゴム（バインダ）とを質量比９８：１：１で含む帯状の負極活物質層を備えた負極シート。
・セパレータ；ポリエチレンの単層からなる長尺状のセパレータシート。
・軸芯；Ｓｎ−Ｂｉの二元合金（融点：１３８℃、質量比はＳｎ：Ｉｎ＝４２：５８）からなる芯部の表面がポリイミドコーティングされており、略角丸長方形状を有する軸芯。
〔電解液〕 エチレンカーボネートとエチルメチルカーボネートとジメチルカーボネートとの体積比が３：３：４の混合溶媒に、１ｍｏｌ／ＬのＬｉＰＦ６（支持塩）を溶解させたもの。
〔電池ケース〕 縦７５ｍｍ×幅１２０ｍｍ×厚さ１５ｍｍ、ケースの厚さ１ｍｍ、アルミ製のケース。 In this test example, three secondary batteries (Examples and Comparative Examples 1 and 2) that differ only in the axial core portion of the wound electrode body were constructed, and the behavior during overcharge and the battery characteristics under a low temperature environment confirmed.
<Example>
In constructing the secondary battery according to the example, the following battery constituent members were prepared.
[For winding electrode assembly]
・ Positive electrode: LiNi 1/3 Co 1/3 Mn 1/3 O 2 (positive electrode active material), acetylene black (conductive material), and polyvinylidene fluoride (on the both sides of a long aluminum foil (positive electrode current collector)) A positive electrode sheet provided with a belt-like positive electrode active material layer containing a binder) at a mass ratio of 90: 8: 2.
-Negative electrode: Graphite (negative electrode active material), carboxymethylcellulose (thickener), and styrene butadiene rubber (binder) at a mass ratio of 98: 1: 1 on both sides of a long copper foil (negative electrode current collector) A negative electrode sheet comprising a strip-shaped negative electrode active material layer.
-Separator: A long separator sheet made of a single layer of polyethylene.
・ Shaft core: A shaft core made of Sn-Bi binary alloy (melting point: 138 ° C., mass ratio: Sn: In = 42: 58) is coated with polyimide and has a substantially rounded rectangular shape. .
[Electrolytic Solution] A solution obtained by dissolving 1 mol / L LiPF 6 (supporting salt) in a mixed solvent having a volume ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate of 3: 3: 4.
[Battery Case] Length 75 mm × width 120 mm × thickness 15 mm, case thickness 1 mm, aluminum case.

次に、上記用意した正極シートおよび負極シートを、セパレータシートを介して重ね合わせ、略角丸長方形状の軸芯の周りに捲回した。これにより扁平形状の捲回電極体を得た。次に、捲回電極体の幅方向の両端部分（活物質層比形成部分）に集電板を溶接した後、直方体形状の電池ケース内に収容し、電池ケース本体と蓋板を溶接した。そして、蓋板に設けられた注液孔から電解液を注入した。最後に、注液孔を封止して図１（ａ）に模式的に示すような二次電池を構築した。   Next, the prepared positive electrode sheet and negative electrode sheet were overlapped via a separator sheet and wound around a substantially rounded rectangular shaft core. Thus, a flat wound electrode body was obtained. Next, the current collector plate was welded to both end portions (active material layer ratio forming portions) in the width direction of the wound electrode body, and then accommodated in a rectangular parallelepiped battery case, and the battery case body and the cover plate were welded. And electrolyte solution was inject | poured from the injection hole provided in the cover plate. Finally, the injection hole was sealed to construct a secondary battery as schematically shown in FIG.

≪比較例≫
比較例１に係る二次電池は、捲回電極体の中心部に軸芯を含まないこと以外は上記実施例と同様の構成である。
また、比較例２に係る二次電池は、特許文献１，４の二次電池に準じて構築した（図２（ａ），（ｂ）を参照。）つまり、比較例１に係る二次電池５０ａでは、捲回電極体１０ａの軸芯１２ａがアルミからなり、かつ、軸芯１２ａの形状が略角丸長方形状でなく略角丸凸形状である。そして、軸芯１２ａの凸形状の幅広部分における端部が、取り付け部材（ねじ）３０によって電池ケース２０と接続されている。それ以外は上記実施例と同様の構成である。 ≪Comparative example≫
The secondary battery according to Comparative Example 1 has the same configuration as that of the above example except that the central part of the wound electrode body does not include an axial core.
The secondary battery according to Comparative Example 2 was constructed in accordance with the secondary battery of Patent Documents 1 and 4 (see FIGS. 2A and 2B). That is, the secondary battery according to Comparative Example 1 was used. In 50a, the shaft core 12a of the wound electrode body 10a is made of aluminum, and the shape of the shaft core 12a is not a substantially rounded rectangular shape but a substantially rounded convex shape. The end of the wide portion of the convex shape of the shaft core 12 a is connected to the battery case 20 by an attachment member (screw) 30. Other than that, the configuration is the same as in the above embodiment.

≪過充電試験≫
０℃の環境下において、上記構築した二次電池を過充電状態まで充電し、その際の挙動を比較した。具体的には、電圧が２５Ｖになるまで１０Ｃのレートで定電流充電し、上限電圧２５Ｖに到達した後に１０秒間の定電圧充電をした。
図３はその際の電池の挙動を示すグラフであり、（ａ）は電圧の推移を、（ｂ）は電池ケースの温度の推移を示している。
図３（ａ）に示すように、電池電圧の挙動は全ての試験例で略同じだった。つまり、過充電となった後も電池に電流を流し続けると、セパレータのシャットダウンが徐々に進行し、それに伴って抵抗が増大する。本過充電試験では電流一定のため、オームの法則に基づいて、上記抵抗の増大によって過電圧が大きくなる。その結果、電池電圧が図３（ａ）に示すような挙動を示す。そして、上限電圧に達した後は、電圧が下降し、やがて０Ｖに近づく。
また、図３（ｂ）に示すように、電池温度の挙動は試験例によって大きく異なっていた。具体的には、比較例１，２では、セパレータのシャットダウン後にも電池温度の上昇が止まらず、最終的にはどちらも熱暴走の状態に陥った。これに対し、実施例では、セパレータのシャットダウン後に電池温度の上昇が抑制され、電池自体には不具合が生じることなく試験を終えた。このことから、実施例の構成は過充電耐性を向上する観点から有効であることが確認された。 ≪Overcharge test≫
Under the environment of 0 ° C., the constructed secondary battery was charged to an overcharged state, and the behavior at that time was compared. Specifically, constant current charging was performed at a rate of 10 C until the voltage reached 25 V, and after reaching the upper limit voltage 25 V, constant voltage charging was performed for 10 seconds.
FIG. 3 is a graph showing the behavior of the battery at that time, where (a) shows the change in voltage and (b) shows the change in temperature of the battery case.
As shown in FIG. 3A, the behavior of the battery voltage was substantially the same in all the test examples. That is, if the current continues to flow through the battery even after overcharging, the shutdown of the separator proceeds gradually, and the resistance increases accordingly. Since the current is constant in this overcharge test, the overvoltage increases due to the increase in the resistance based on Ohm's law. As a result, the battery voltage behaves as shown in FIG. Then, after reaching the upper limit voltage, the voltage drops and eventually approaches 0V.
Further, as shown in FIG. 3B, the behavior of the battery temperature was greatly different depending on the test example. Specifically, in Comparative Examples 1 and 2, the increase in battery temperature did not stop even after the separator was shut down, and both eventually entered a state of thermal runaway. On the other hand, in the examples, the rise in the battery temperature was suppressed after the shutdown of the separator, and the test was completed without causing any defects in the battery itself. From this, it was confirmed that the structure of an Example is effective from a viewpoint of improving overcharge tolerance.

≪低温ハイレート試験≫
−２０℃の環境下において、上記構築した二次電池をハイレート放電し、その際の電圧の挙動を比較した。具体的には、上記二次電池をＳＯＣ２５％の状態に調整した後、５Ｃのレートで２０秒間のパルス放電を行った。
図４はその際の電圧の推移を示している。図４に示すように、比較例２では、パルス放電時の電圧低下量が大きかった。つまり、比較例２は、低温環境下で抵抗が増大しており、電池特性が相対的に低かった。これに対し、実施例および比較例１は、電圧降下量が相対的に少なく、低温環境下での電池特性に優れることが確認された。 ≪Low temperature high rate test≫
Under the environment of −20 ° C., the secondary battery constructed as described above was discharged at a high rate, and the behavior of voltage at that time was compared. Specifically, after the secondary battery was adjusted to a state of SOC 25%, pulse discharge for 20 seconds was performed at a rate of 5C.
FIG. 4 shows the voltage transition at that time. As shown in FIG. 4, in Comparative Example 2, the amount of voltage drop during pulse discharge was large. That is, in Comparative Example 2, the resistance increased in a low temperature environment, and the battery characteristics were relatively low. On the other hand, it was confirmed that Example and Comparative Example 1 have a relatively small amount of voltage drop and are excellent in battery characteristics in a low temperature environment.

上記の結果から明らかなように、ここで開示される技術によれば低温環境下での優れた電池特性と過充電時の高い信頼性とを兼ね備えた二次電池を実現することができる。   As is apparent from the above results, according to the technology disclosed herein, a secondary battery having both excellent battery characteristics under a low temperature environment and high reliability during overcharge can be realized.

以上、本発明を詳細に説明したが、上記実施形態および実施例は例示にすぎず、ここで開示される発明には上述の具体例を様々に変形、変更したものが含まれる。   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.

１０，１０ａ 捲回電極体
１２，１２ａ 軸芯
１４ 正極活物質層非形成部分
１５ 正極集電板
１６ 負極活物質層非形成部分
１７ 負極集電板
２０ 電池ケース
２２ 電池ケース本体
２４ 蓋板
２６ 正極端子
２８ 負極端子
３０ 取り付け部材（ねじ）
５０，５０ａ 二次電池 DESCRIPTION OF SYMBOLS 10, 10a Winding electrode body 12, 12a Shaft core 14 Positive electrode active material layer non-formation part 15 Positive electrode current collecting plate 16 Negative electrode active material layer non-formation part 17 Negative electrode current collection plate 20 Battery case 22 Battery case main body 24 Cover plate 26 Positive electrode Terminal 28 Negative electrode terminal 30 Mounting member (screw)
50, 50a secondary battery

Claims (1)

正極および負極がセパレータを介して重ね合わされ軸芯の周りに捲回された構造の電極体と、電解液と、を備える二次電池であって、
前記セパレータは、シャットダウン機能を有し、
前記軸芯は、前記セパレータのシャットダウン温度以上であって前記正極の熱分解温度よりも低い温度域で吸熱反応を生じる金属材料を有し、前記軸芯の表面は、前記金属材料よりも熱伝導性が低い樹脂材料によってコートされている、二次電池。 An electrode body having a structure in which a positive electrode and a negative electrode are overlapped via a separator and wound around an axis, and an electrolyte,
The separator has a shutdown function,
The shaft core includes a metal material that generates an endothermic reaction in a temperature range that is equal to or higher than the shutdown temperature of the separator and lower than the thermal decomposition temperature of the positive electrode, and the surface of the shaft core is more thermally conductive than the metal material. A secondary battery that is coated with a low-resin resin material.
JP2015027538A 2015-02-16 2015-02-16 Secondary battery Pending JP2016152071A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106654076A (en) * 2017-01-22 2017-05-10 湖州百成电池有限公司 Method and structure for improving security performance of secondary lithium battery
JP2018206628A (en) * 2017-06-06 2018-12-27 トヨタ自動車株式会社 Nonaqueous electrolyte secondary battery
JP2019071255A (en) * 2017-10-11 2019-05-09 Tdk株式会社 Electrochemical device and electrochemical device pack
WO2019245343A1 (en) * 2018-06-22 2019-12-26 주식회사 엘지화학 Separator for electrochemical device, electrochemical device comprising same, and method for manufacturing separator
JP2020109732A (en) * 2019-01-07 2020-07-16 株式会社Ｓｏｋｅｎ Secondary battery

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106654076A (en) * 2017-01-22 2017-05-10 湖州百成电池有限公司 Method and structure for improving security performance of secondary lithium battery
JP2018206628A (en) * 2017-06-06 2018-12-27 トヨタ自動車株式会社 Nonaqueous electrolyte secondary battery
JP2019071255A (en) * 2017-10-11 2019-05-09 Tdk株式会社 Electrochemical device and electrochemical device pack
WO2019245343A1 (en) * 2018-06-22 2019-12-26 주식회사 엘지화학 Separator for electrochemical device, electrochemical device comprising same, and method for manufacturing separator
JP2020109732A (en) * 2019-01-07 2020-07-16 株式会社Ｓｏｋｅｎ Secondary battery
JP7189027B2 (en) 2019-01-07 2022-12-13 株式会社Soken secondary battery

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