JP2004006264A

JP2004006264A - Lithium secondary battery

Info

Publication number: JP2004006264A
Application number: JP2003069033A
Authority: JP
Inventors: Yuichi Takatsuka; 高塚　祐一; Tetsuhisa Sakai; 酒井　哲久
Original assignee: Shin Kobe Electric Machinery Co Ltd
Current assignee: Resonac Corp
Priority date: 2002-04-17
Filing date: 2003-03-14
Publication date: 2004-01-08

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution secondary battery superior in safety. <P>SOLUTION: A cylindrical lithium ion secondary battery has an electrode group and a nonaqueous electrolytic solution in a battery can. As for the electrode group, a positive electrode using as a positive electrode active substance lithium manganate in which the gross calorific value by DSC is 1.0 (kJ/g) or less, the maximum heating peak output is 9 (W/g) or less, and the maximum heating temperature is 300 (°C) or more, and a negative electrode using amorphous carbon as a negative electrode active substance are wound through a separator. The gross calorific value of the lithium manganate is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明はリチウム二次電池に係り、特に、正極活物質にスピネル構造を有するリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いた正極と、負極活物質に炭素材を用いた負極とを非水電解液に浸潤させたリチウム二次電池に関する。
【０００２】
【従来の技術】
近年、電気機器の小型化、軽量化の進展に伴い高エネルギー密度を有するリチウム二次電池の研究・開発が進められている。現在では、携帯電話やノートパソコン向けに小型民生用のリチウム二次電池が広く普及している。
【０００３】
また、地球温暖化や枯渇燃料の問題から、電気自動車（ＥＶ）や駆動の一部を電気モーターで補助するハイブリッド電気自動車（ＨＥＶ）が自動車メーカーで開発され、それらの電源に用いられる電池にはより高エネルギー密度、高出力が求められるようになってきている。このような要求に合致する電源としても、高電圧を有するリチウム二次電池が注目されている。
【０００４】
リチウム二次電池の負極材には一般的に炭素材が用いられる。一方、正極材には一般的にリチウム遷移金属酸化物が用いられる。リチウム遷移金属酸化物の中でも容量やサイクル特性等のバランスからリチウムコバルト複合酸化物やリチウムニッケル複合酸化物が一般的に用いられている。しかし、リチウムマンガン複合酸化物を正極材に用いる方がこれらよりコスト面、安全面で有利なことから、ＥＶ／ＨＥＶ用電池の正極材としてリチウムマンガン複合酸化物が有望視されている。このようなリチウムイオン電池の正極活物質には、スピネル構造を有するリチウム複合酸化物（例えば、特許文献１参照）や層状構造を有する複合酸化物（例えば、特許文献２参照）が用いられる。
【０００５】
また、リチウム二次電池の過充電時の安全性対策として、電池温度の上昇に応じて電気的に作動するＰＴＣ（Ｐｏｓｉｔｉｖｅ　Ｔｅｍｐｅｒａｔｕｒｅ　Ｃｏｅｆｆｉｃｉｅｎｔ）素子や電池内圧上昇を利用した圧力スイッチによる電流遮断機構を利用して、電池内圧が極端に上昇する前に、過充電を停止させている。
【０００６】
【特許文献１】
特開２００２−３１６８２３号公報
【特許文献２】
特開２００２−０６８７４７号公報
【０００７】
【発明が解決しようとする課題】
しかしながら、大電流を取り出す必要のある電池の場合に、ＰＴＣ素子による抵抗の増加や圧力スイッチの接点部分の発熱が生じるため、蓋などに安全機構を設けることは難しい。充電中に外部構造の安全機構による電流遮断ができないときには、電池は過充電され続け、正極活物質のリチウムマンガン複合酸化物からリチウムイオンが全て抜け出し電圧の上昇に伴いその構造が不安定化し、更に非水電解液の分解が開始する。この分解による発熱は部分的に急激な温度上昇を示す。これにより、不安定化したリチウムマンガン複合酸化物の酸素が、急激に非水電解液の酸化、分解に消費されて、更に大きな発熱量を生じ、電池から白煙や発火を発生させる。このため、過充電状態になっても安全性を保持することができる正極が望まれている。
【０００８】
本発明は上記問題に鑑み、安全性に優れたリチウム二次電池を提供することを課題とする。
【０００９】
【課題を解決するための手段】
上記課題を解決するために、本発明は、正極活物質にスピネル構造を有するリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いた正極と、負極活物質に炭素材を用いた負極とを非水電解液に浸潤させたリチウム二次電池において、前記リチウムマンガン複合酸化物の示差走査熱量計による発熱の総量が１．０ｋＪ／ｇ以下であることを特徴とする。
【００１０】
本発明では、高エネルギー密度、高出力のリチウム二次電池を確保するために、正極活物質にリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いた正極と、負極活物質に炭素材を用いた負極とが使用されている。高エネルギー密度、高出力のリチウム二次電池では、過充電状態に陥ったときに、活物質と非水電解液との化学反応により電池容器内で急激にガスが発生し、電池容器の内圧を上昇させ、発熱により電池の表面温度を上昇させる。本発明によれば、正極活物質に示差走査熱量計による示差走査熱量計による発熱の総量が１．０ｋＪ／ｇ以下のリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いることで、複合酸化物の発熱の総量を抑制することができるので、安全性に優れた非水電解液二次電池を実現することができる。
【００１１】
この場合において、示差走査熱量計による最大発熱ピーク出力が９Ｗ／ｇ以下のリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いることで、より安全性に優れた非水電解液二次電池とすることができる。更に、示差走査熱量計による最大発熱ピーク温度が３００゜Ｃ以上のリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いることで、複合酸化物の酸素放出の温度を高め、非水電解液の分解を抑制することができるので、更に安全性に優れた非水電解液二次電池とすることができる。
【００１２】
【発明の実施の形態】
以下、図面を参照して本発明に係るリチウム二次電池を円筒型リチウムイオン二次電池に適用した実施の形態について説明する。
【００１３】
（負極）
負極活物質としての非晶質炭素粉末９０重量部に、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）１０重量部を添加し、これに分散溶媒としてＮ−メチルピロリドン（ＮＭＰ）を添加、混練したスラリを厚さ１０μｍの圧延銅箔の両面に塗布し、乾燥させた後、プレス、裁断して負極を得た。
【００１４】
（正極）
正極活物質としてリチウムマンガン複合酸化物の粉末９０重量部に対して、導電材として炭素粉末５重量部と、結着剤としてポリフッ化ビニリデン５重量部と、を添加し、これに分散溶媒としてＮ−メチルピロリドンを添加、混練したスラリを、厚さ２０μｍのアルミニウム箔の両面に均一に塗布し、乾燥させた後、プレス、裁断して正極を得た。上述したリチウムマンガン複合酸化物は、マンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）又はＬｉＭｎ_２Ｏ_４のリチウムサイト又はマンガンサイトを他の金属元素で置換又はドープした、例えば、化学式Ｌｉ_１＋ｘＭ_ｙＭｎ_{２−ｘ−ｙ}Ｏ_４（ＭはＬｉ、Ｃｏ、Ｎｉ、Ｆｅ、Ｃｕ、Ａｌ、Ｃｒ、Ｍｇ、Ｚｎ、Ｖ、Ｇａ、Ｂ、Ｆ）を用いることができる。また、リチウムマンガン複合酸化物の代わりに、Ｌｉ、Ｍｎ、Ｃｏ、Ｎｉを含む層状構造の複合酸化物も用いることができる。
【００１５】
ＬｉＭｎ_２Ｏ_４のマンガンの原料として二酸化マンガン、硫酸マンガン、硝酸マンガン、酢酸マンガンなどのマンガン化合物を、リチウムの原料として炭酸リチウム、硝酸リチウム、酢酸リチウム、硫化リチウム等のリチウム化合物を使用した。スピネル系リチウムマンガン複合酸化物の場合には、金属元素を含んだ、炭酸塩、硝酸塩、硫酸塩、酢酸塩などの塩を原料に使用した。また、Ｌｉ、Ｍｎ、Ｃｏ、Ｎｉを含む層状構造の複合酸化物の原料は、マンガン原料として二酸化マンガン、硫酸マンガン、硝酸マンガン、酢酸マンガンなどのマンガン化合物、コバルト原料としてコバルト酸化物、硫酸コバルト、硝酸コバルトなどのコバルト化合物、ニッケル原料としてニッケル酸化物、硫酸ニッケル、硝酸ニッケルなどのニッケル化合物、リチウム原料として炭酸リチウム、硝酸リチウム、酢酸リチウム、硫化リチウムなどのリチウム化合物を使用する。別の元素を置換・ドープする場合は、その元素を含む炭酸塩、硝酸塩、硫酸塩、酢酸塩などの塩を使用する。各原料の混合比を調整し均一に混合し、焼成温度、焼成温度を変えることで、スピネル構造を有するリチウムマンガン複合酸化物、及び、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を調製する（以下、両者を総称する場合に「複合酸化物」という。）。
【００１６】
ＤＳＣによる正極活物質の最大発熱ピーク温度は次のようにして求めた。上述したように作製した正極を、ポリエチレン製セパレータを介して、金属リチウムを銅メッシュに貼り付けた負極で挟み込み、電解液に浸潤させてビーカーセルとした。電解液には、６フッ化リン酸リチウム（ＬｉＰＦ_６）をエチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）とを１：２の体積割合で混合した溶媒に溶解した非水電解液を用いた。次にビーカーセルを電流密度０．５ｍＡ／ｃｍ^２で過充電し、６．５Ｖとなるまで充電した。そのビーカーセルをドライボックス中で解体し、正極を取り出し、ＤＭＣで洗浄後、乾燥させた。更に、この正極を集電体ごとφ３ｍｍのポンチで打ち抜き、ＤＳＣ測定用のＳＵＳ製密閉容器に１．５μｌの非水電解液と共に入れ、密閉した。なお、非水電解液は、ビーカーセルで使用したものと同様のものを使用した。
【００１７】
ＤＳＣは、一般に物質の熱容量等を測定する熱量計として用いられている。試料（正極活物質）と参照物質とに等しい熱量（エネルギー）を与えつつ同時に昇温させ、相転移や分解が起こると、試料は熱を吸収するため試料の温度上昇が遅れて参照物質との間に温度差を生じようとする。ＤＳＣは、この温度差をゼロに保つに必要なエネルギーを各時間（又は試料の温度）毎に測定することができる。正極活物質と参照物質とに加えたエネルギーの差が最大となるときの正極活物質の温度を最大発熱ピーク温度とした。
【００１８】
ＤＳＣ測定には、ＤＳＣ８２３０（リガク製）を使用した。ＤＳＣ測定時の昇温速度は、１０゜Ｃ／ｍｉｎとした。ＤＳＣ測定データから、それぞれの複合酸化物を使用した場合の総発熱量（ｋＪ／ｇ）、最大発熱ピーク出力（Ｗ／ｇ）、最大発熱ピーク温度（゜Ｃ）を読み取った。
【００１９】
（電池の作製）
図１に示すように、上記正負極を、これら両極が直接接触しないように厚さ４０μｍのポリオレフィン系セパレータを介して、捲回中心となる軸芯１１の周りに捲回して電極群６を作製した。このとき、正極板及び負極板のリード片９が、それぞれ電極群６の互いに反対側の両端面に位置するようにした。
【００２０】
電極群６の最内周では捲回方向に正極板が負極板からはみ出すことがなく、また、最外周でも捲回方向に正極板が負極板からはみ出すことがないように、負極板の長さは正極板の長さよりも１８ｃｍ長くなるようにした。捲回方向に垂直の方向においても正極活物質塗布部が負極活物質塗布部からはみ出すことがないように、負極活物質塗布部の幅を、正極活物質塗布部の幅よりも５ｍｍ長くした。
【００２１】
正極板から導出されているリード片９を変形させ、その全てを、軸芯１１のほぼ延長線上にある正極外部端子１周囲から一体に張り出している鍔部７周面付近に集合、接触させた後、リード片９と鍔部７周面とを超音波溶接してリード片９を鍔部７周面に接続し固定した。また、負極外部端子１’と負極板から導出されているリード片９との接続操作も、正極外部端子１と正極板から導出されているリード片９との接続操作と同様に行った。
【００２２】
その後、正極外部端子１及び負極外部端子１’の鍔部７周面全周に絶縁被覆８を施した。この絶縁被覆８は、電極群６外周面全周にも及ぼした。絶縁被覆８には、基材がポリイミドで、その片面にヘキサメタアクリレートからなる粘着剤を塗布した粘着テープを用いた。この粘着テープを鍔部７周面から電極群６外周面に亘って何重にも巻いて絶縁被覆８とした。電極群６の最大径部が絶縁被覆８存在部となるように巻き数を調整し、直径６５ｍｍ、高さ３９０ｍｍの円筒状でＳＵＳ製の電池容器５の内径よりも僅かに小さくして、電極群６を電池容器５内に挿入する。
【００２３】
そして、アルミナ製で円盤状電池蓋４裏面と当接する部分の厚さ２ｍｍ、内径１６ｍｍ、外径２５ｍｍの第２のセラミックワッシャ３’を、図１に示すように、先端が正極外部端子１を構成する極柱、先端が負極外部端子１’を構成する極柱にそれぞれ嵌め込んだ。また、アルミナ製で厚さ２ｍｍ、内径１６ｍｍ、外径２８ｍｍの平板状の第１のセラミックワッシャ３を電池蓋４に載置し、正極外部端子１、負極外部端子１’をそれぞれ第１のセラミックワッシャ３に通した。その後、電池蓋４周端面を電池容器５開口部に嵌合し、双方の接触部全域をレーザ溶接した。このとき、正極外部端子１、負極外部端子１’は、電池蓋４の中心に形成された穴を貫通して電池蓋４外部に突出している。そして、図１に示すように、第１のセラミックワッシャ３、金属製ナット２底面よりも平滑な金属ワッシャ１４を、この順に正極外部端子１、負極外部端子１’にそれぞれ嵌め込んだ。なお、電池蓋４には電池の内圧上昇に応じて開裂するアルミニウム合金製で板状の開裂弁１０が設けられている。開裂弁１０の開裂圧は、約９×１０^５とした。
【００２４】
次いで、ナット２を正極外部端子１、負極外部端子１’にそれぞれ螺着し、第２のセラミックワッシャ３’、第１のセラミックワッシャ３、金属ワッシャ１４を介して電池蓋４を鍔部７とナット２の間で締め付けにより固定した。このときの締め付けトルク値は７Ｎ・ｍとした。なお、締め付け作業が終了するまで金属ワッシャ１４は回転しなかった。この状態で、電池蓋４裏面と鍔部７の間に介在させたゴム（ＥＰＤＭ）製Ｏリング１６の圧縮により電池容器５内部の発電要素は外気から遮断される。
【００２５】
その後、電池蓋４に設けた注液口１５から上述と同様に調製した非水電解液を所定量電池容器５内に注入して、その後注液口１５を封止することにより容量９０Ａｈ、出力１０００Ｗ以上の円筒型リチウムイオン二次電池２０を組み立てた。
【００２６】
【実施例】
次に、本実施形態に従って作製した円筒型リチウムイオン二次電池２０の実施例について説明する。なお、比較のために作製した比較例の電池についても併記する。
【００２７】
（比較例１）
下表１に示すように、比較例１では、正極活物質に、総発熱量が１．１（ｋＪ／ｇ）、最大発熱ピーク出力が２５（Ｗ／ｇ）、最大発熱ピーク温度が２８０（゜Ｃ）の複合酸化物ａを用いて電池を作製した。
【００２８】
【表１】

【００２９】
（比較例２）
比較例２では、正極活物質に、最大発熱ピーク出力が１３（Ｗ／ｇ）の複合酸化物ｂを用いた以外は、比較例１と同様にして電池を作製した。
【００３０】
（実施例１）
実施例１では、正極活物質に、総発熱量が１．０（ｋＪ／ｇ）、最大発熱ピーク出力が１３（Ｗ／ｇ）の複合酸化物ｃを用いた以外は、比較例１と同様にして電池を作製した。
【００３１】
（実施例２〜４）
実施例２〜実施例４では、正極活物質に、それぞれ総発熱量が０．８（ｋＪ／ｇ）、最大発熱ピーク温度が２９０（゜Ｃ）、最大発熱ピーク出力が１０、９、７（Ｗ／ｇ）の複合酸化物ｄ〜ｆを用いた以外は、比較例１と同様にして電池を作製した。
【００３２】
（実施例５）
実施例５では、正極活物質に、総発熱量が０．８（ｋＪ／ｇ）、最大発熱ピーク出力が７（Ｗ／ｇ）、最大発熱ピーク温度が３００（゜Ｃ）の複合酸化物ｇを用いた以外は、比較例１と同様にして電池を作製した。
【００３３】
（比較例３、４）
比較例３では、正極活物質に、総発熱量が１．３（ｋＪ／ｇ）、最大発熱ピーク出力が２８（Ｗ／ｇ）、最大発熱ピーク温度が２８０（゜Ｃ）の複合酸化物ｈを用いて電池を作製した。比較例４では、正極活物質に、総発熱量が１．１（ｋＪ／ｇ）、最大発熱ピーク出力が１５（Ｗ／ｇ）の複合酸化物ｉを用いた以外は、比較例３と同様にして電池を作製した。
【００３４】
（実施例６）
実施例６では、正極活物質に、総発熱量が１．０（ｋＪ／ｇ）、最大発熱ピーク出力が１５（Ｗ／ｇ）の複合酸化物ｊを用いた以外は、比較例３と同様にして電池を作製した。
【００３５】
（実施例７〜９）
実施例７〜９では、正極活物質に、それぞれ総発熱量が０．９、０．８、０．９（ｋＪ／ｇ）、最大発熱ピーク出力が１０、９、８（Ｗ／ｇ）、最大発熱ピーク温度が２８０、２９０、２８０（°Ｃ）の複合酸化物ｋ、ｌ、ｍを用いた以外は、比較例３と同様にして電池を作製した。
【００３６】
実施例１０では、正極活物質に、総発熱量が０．９（ｋＪ／ｇ）、最大発熱ピーク出力が８（Ｗ／ｇ）、最大発熱ピーク温度が３００（°Ｃ）の複合酸化物ｎを用いた以外は、比較例３と同様にして電池を作製した。
【００３７】
なお、上記実施例及び比較例で、複合酸化物ａ〜ｇはスピネル構造を有するリチウムマンガン複合酸化物であり、複合酸化物ｈ〜ｎはリチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物である。
【００３８】
＜試験・評価＞
次に、以上のように作製した実施例及び比較例の各電池について、０．５Ｃの電流を充電方向に連続的に流す過充電試験を行い、このときの電池缶７表面の最高到達温度を測定した。発火の有無の状況についても調べた。下表２に測定した最高到達温度及び発火の有無の結果を示す。
【００３９】
【表２】

【００４０】
表２に示すように、スピネル構造を有するリチウムマンガン複合酸化物のＤＳＣの総発熱量が１．０（ｋＪ／ｇ）以下の実施例の電池では、過充電時の発火現象がなくなり、煙の噴出のみとなった。最大発熱ピーク出力が９Ｗ／ｇ以下の実施例３〜実施例５の電池では、煙の噴出程度が非常に緩やかになった。更に、最大発熱ピーク温度が３００゜Ｃ以上の実施例５の電池では、電池表面の最高到達温度１１５゜Ｃと低くすることができた。同様に、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いた正極でもＤＳＣの総発熱量が１．０（ｋＪ／ｇ）以下の実施例の電池では、過充電時の発火現象がなくなり、煙の噴出のみとなった。最大発熱ピーク出力が９Ｗ／ｇ以下の実施例８〜実施例１０の電池では、煙の噴出程度が非常に緩やかになった。更に、最大発熱ピーク温度が３００゜Ｃ以上の実施例１０の電池では、電池表面の最高到達温度１２５゜Ｃと低くすることができた。
【００４１】
以上の試験結果から、総発熱量が１．０（ｋＪ／ｇ）以下、最大発熱ピーク出力が９（Ｗ／ｇ）以下、最大発熱ピーク温度が３００（゜Ｃ）以上の複合酸化物を正極活物質に用いた電池は、安全性に優れていることが分かった。
【００４２】
なお、上記実施例では、正極活物質にスピネル構造を有するリチウムマンガン複合酸化物を用いた例を示したが、ＬｉＭｎ_２Ｏ_４のリチウムサイト又はマンガンサイトを他の金属元素（例えば、Ｌｉ、Ｃｏ、Ｎｉ、Ｆｅ、Ｃｕ、Ａｌ、Ｃｒ、Ｍｇ、Ｚｎ、Ｖ、Ｇａ、Ｂ、Ｆの少なくとも１種）で置換又はドープしたスピネル系リチウムマンガン複合酸化物を用いるようにしてもよい。また、上記の実施例では、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いた例を示したが、他の金属元素で置換した層状構造の複合酸化物を用いるようにしてもよい。
【００４３】
また、本実施形態では、正極活物質、導電材及び結着剤の配合比を９０：５：５とした例を示したが、配合比はこれに限定されず、例えば、８５：１０：５とした場合にも本発明が適用可能であることは論を待たない。
【００４４】
更に、本実施形態では、負極活物質に非晶質炭素を用いた例を示したが、これに限定されるものではなく、リチウムイオンを挿入、脱挿入可能な天然黒鉛や、人造の各種黒鉛材、コークスなどの炭素質材料等でよく、粒子形状においても、鱗片状、球状、繊維状、塊状等、特に制限されるものではない。
【００４５】
更にまた、本実施形態では、電解質としてＬｉＰＦ_６を用いた例を示したが、これに限定されるものではなく、例えば、ＬｉＣｌＯ_４、ＬｉＡｓＦ_６、ＬｉＢＦ_４、ＬｉＢ（Ｃ_６Ｈ_５）_４、ＣＨ_３ＳＯ_３Ｌｉ、ＣＦ_３ＳＯＬｉなどやこれらの混合物を用いることができる。また、本実施形態では、非水電解液の溶媒にＥＣとＤＭＣとの混合溶媒を用いた例を示したが、プロピレンカーボネート、エチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、１，２−ジメトキシエタン、１，２−ジエトキシエタン、γ―ブチルラクトン、テトラヒドロフラン、１，３−ジオキソラン、４−メチル−１，３−ジオキソラン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、プロピオニトリル、プロピオニトリルなど少なくとも１種以上の混合溶媒を用いるようにしてもよく、混合配合比についても限定されるものではない。
【００４６】
また更に、本実施形態では、結着材にＰＶＤＦを用いた例を示したが、ポリエチレンテレフタレート、ポリエチレン、ポリスチレン、ポリブタジエン、ブチルゴム、ニトリルゴム、スチレン／ブタジエンゴム、多硫化ゴム、ニトロセルロース、シアノエチルセルロース、各種ラテックス、アクリロニトリル、フッ化ビニル、フッ化ビニリデン、フッ化プロピレン、フッ化クロロプレン、アクリル系樹脂などの重合体及びこれらの混合体などを用いることができる。
【００４７】
また、本実施形態では、電池容器に円筒状の電池缶を使用した例を示したが、本発明は電池の形状についても限定されず、角型、その他の多角形の電池、積層タイプの電池にも適用可能である。
【００４８】
【発明の効果】
以上説明したように、本発明によれば、正極活物質に示差走査熱量計による示差走査熱量計による発熱の総量が１．０ｋＪ／ｇ以下のリチウムマンガン複合酸化物、又は、リチウム、マンガン、コバルト及びニッケルを含む層状構造の複合酸化物を用いることで、複合酸化物の発熱の総量を抑制することができるので、安全性に優れた非水電解液二次電池を実現することができる、という効果を得ることができる。
【図面の簡単な説明】
【図１】本発明が適用可能な実施形態の円筒型リチウムイオン二次電池の断面図である。
【符号の説明】
２０　円筒型リチウムイオン二次電池（リチウム二次電池）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium secondary battery, in particular, a positive electrode using a lithium manganese composite oxide having a spinel structure as a positive electrode active material, or a layered composite oxide containing lithium, manganese, cobalt, and nickel, and a negative electrode The present invention relates to a lithium secondary battery in which a negative electrode using a carbon material as an active material is infiltrated in a nonaqueous electrolyte.
[0002]
[Prior art]
2. Description of the Related Art In recent years, research and development of lithium secondary batteries having a high energy density have been promoted with the progress of miniaturization and weight reduction of electric devices. At present, lithium-ion rechargeable batteries for small consumers for mobile phones and notebook computers are widely used.
[0003]
Also, due to global warming and the problem of depleted fuel, electric vehicles (EV) and hybrid electric vehicles (HEV), in which some of the driving is assisted by electric motors, have been developed by automakers. Higher energy density and higher output are required. As a power source that meets such demands, a lithium secondary battery having a high voltage has attracted attention.
[0004]
Generally, a carbon material is used as a negative electrode material of a lithium secondary battery. On the other hand, a lithium transition metal oxide is generally used for the positive electrode material. Among the lithium transition metal oxides, lithium cobalt composite oxide and lithium nickel composite oxide are generally used because of their balance in capacity and cycle characteristics. However, since using lithium manganese composite oxide as the positive electrode material is more advantageous in terms of cost and safety than these, lithium manganese composite oxide is expected to be promising as a positive electrode material for EV / HEV batteries. As the positive electrode active material of such a lithium ion battery, a lithium composite oxide having a spinel structure (for example, see Patent Literature 1) or a composite oxide having a layered structure (for example, see Patent Literature 2) is used.
[0005]
In addition, as a safety measure at the time of overcharge of the lithium secondary battery, a current interruption mechanism using a PTC (Positive Temperature Coefficient) element that operates electrically in response to a rise in the battery temperature or a pressure switch using a rise in battery internal pressure is used. Then, the overcharge is stopped before the battery internal pressure rises extremely.
[0006]
[Patent Document 1]
JP 2002-316823 A [Patent Document 2]
JP-A-2002-068747
[Problems to be solved by the invention]
However, in the case of a battery that needs to take out a large current, an increase in resistance due to the PTC element and heat generation at the contact portion of the pressure switch occur, so that it is difficult to provide a safety mechanism on a lid or the like. If current cannot be interrupted by the safety mechanism of the external structure during charging, the battery continues to be overcharged, and all lithium ions escape from the lithium manganese composite oxide as the positive electrode active material, and the structure becomes unstable as the voltage rises. Decomposition of the non-aqueous electrolyte starts. The heat generated by this decomposition partially shows a sharp rise in temperature. As a result, the oxygen of the destabilized lithium manganese composite oxide is rapidly consumed by the oxidation and decomposition of the non-aqueous electrolyte, generating a larger amount of heat and causing white smoke and ignition from the battery. Therefore, a positive electrode that can maintain safety even in an overcharged state is desired.
[0008]
In view of the above problems, an object of the present invention is to provide a lithium secondary battery having excellent safety.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a positive electrode using a lithium manganese composite oxide having a spinel structure in a positive electrode active material, or a composite oxide having a layered structure including lithium, manganese, cobalt, and nickel, and a negative electrode. In a lithium secondary battery in which a negative electrode using a carbon material as an active material is impregnated in a nonaqueous electrolyte, the total amount of heat generated by the differential scanning calorimeter of the lithium manganese composite oxide is 1.0 kJ / g or less. It is characterized by.
[0010]
In the present invention, a lithium manganese composite oxide or a layered composite oxide containing lithium, manganese, cobalt and nickel is used as a positive electrode active material in order to secure a high energy density, high output lithium secondary battery. And a negative electrode using a carbon material as a negative electrode active material. In a high-energy density, high-output lithium secondary battery, when an overcharged state occurs, gas is rapidly generated in the battery container due to a chemical reaction between the active material and the non-aqueous electrolyte, and the internal pressure of the battery container is reduced. The surface temperature of the battery is raised by heat generation. According to the present invention, the positive electrode active material has a total amount of heat generated by a differential scanning calorimeter using a differential scanning calorimeter of 1.0 kJ / g or less, or a lithium manganese composite oxide or a layered structure containing lithium, manganese, cobalt, and nickel. Since the total amount of heat generated by the composite oxide can be suppressed by using the composite oxide, a non-aqueous electrolyte secondary battery excellent in safety can be realized.
[0011]
In this case, by using a lithium manganese composite oxide having a maximum exothermic peak output of 9 W / g or less by a differential scanning calorimeter or a layered composite oxide containing lithium, manganese, cobalt, and nickel, more safety can be obtained. A non-aqueous electrolyte secondary battery having excellent characteristics can be obtained. Further, by using a lithium manganese composite oxide having a maximum exothermic peak temperature of 300 ° C. or higher by a differential scanning calorimeter or a layered composite oxide containing lithium, manganese, cobalt, and nickel, the oxygen of the composite oxide can be reduced. Since the release temperature can be increased and the decomposition of the non-aqueous electrolyte can be suppressed, a non-aqueous electrolyte secondary battery with even higher safety can be obtained.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which a lithium secondary battery according to the present invention is applied to a cylindrical lithium ion secondary battery will be described with reference to the drawings.
[0013]
(Negative electrode)
A slurry obtained by adding 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder to 90 parts by weight of amorphous carbon powder as a negative electrode active material, adding N-methylpyrrolidone (NMP) as a dispersion solvent thereto, and kneading the slurry. Was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, and then pressed and cut to obtain a negative electrode.
[0014]
(Positive electrode)
5 parts by weight of carbon powder as a conductive material and 5 parts by weight of polyvinylidene fluoride as a binder were added to 90 parts by weight of lithium manganese composite oxide powder as a positive electrode active material, and N was added as a dispersing solvent to this. A slurry obtained by adding and kneading methylpyrrolidone was uniformly applied to both surfaces of an aluminum foil having a thickness of 20 μm, dried, and then pressed and cut to obtain a positive electrode. Lithium manganese composite oxide described above, lithium manganese acid (LiMn ₂ O ₄₎ or lithium site LiMn ₂ O ₄ or manganese site was replaced or doped with other metal elements, for example, the formula _Li 1 ₊ x M y _{Mn 2- _x-y} _O 4 (M is Li, Co, Ni, Fe, Cu, Al, Cr, Mg, Zn, V, Ga, B, F) can be used. Instead of the lithium manganese composite oxide, a composite oxide having a layered structure containing Li, Mn, Co, and Ni can also be used.
[0015]
A manganese compound such as manganese dioxide, manganese sulfate, manganese nitrate, or manganese acetate was used as a raw material for manganese of LiMn ₂ O ₄ , and a lithium compound such as lithium carbonate, lithium nitrate, lithium acetate, or lithium sulfide was used as a raw material for lithium. In the case of the spinel lithium manganese composite oxide, a salt containing a metal element, such as a carbonate, a nitrate, a sulfate, and an acetate, was used as a raw material. Further, the raw materials of the composite oxide having a layered structure containing Li, Mn, Co, and Ni are manganese compounds such as manganese dioxide, manganese sulfate, manganese nitrate, and manganese acetate as manganese raw materials, and cobalt oxide and cobalt sulfate as cobalt raw materials. A cobalt compound such as cobalt nitrate, a nickel compound such as nickel oxide, nickel sulfate and nickel nitrate as a nickel raw material, and a lithium compound such as lithium carbonate, lithium nitrate, lithium acetate and lithium sulfide as a lithium raw material are used. When substituting or doping another element, a salt containing that element, such as a carbonate, a nitrate, a sulfate, or an acetate, is used. Lithium-manganese composite oxide having a spinel structure and composite oxide having a layered structure containing lithium, manganese, cobalt and nickel by adjusting the mixing ratio of each raw material, mixing uniformly, and changing the firing temperature and firing temperature (Hereinafter, when both are collectively referred to as “composite oxide”).
[0016]
The maximum exothermic peak temperature of the positive electrode active material by DSC was determined as follows. The positive electrode prepared as described above was sandwiched between negative electrodes each having lithium metal adhered to a copper mesh via a polyethylene separator, and was infiltrated with an electrolytic solution to form a beaker cell. As the electrolytic solution, a non-aqueous electrolytic solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 2 was used. Next, the beaker cell was overcharged at a current density of 0.5 mA / cm ² and charged to 6.5 V. The beaker cell was disassembled in a dry box, the positive electrode was taken out, washed with DMC, and dried. Further, the positive electrode was punched together with the current collector with a punch having a diameter of 3 mm, placed in a SUS sealed container for DSC measurement together with 1.5 μl of a nonaqueous electrolyte, and sealed. The nonaqueous electrolyte used was the same as that used in the beaker cell.
[0017]
DSC is generally used as a calorimeter for measuring the heat capacity and the like of a substance. When the same amount of heat (energy) as the sample (positive electrode active material) and the reference material is applied and the temperature is raised at the same time, and phase transition or decomposition occurs, the sample absorbs heat and the temperature rise of the sample is delayed, causing the sample to absorb heat. Try to create a temperature difference between them. The DSC can measure the energy required to keep this temperature difference at zero each time (or the temperature of the sample). The temperature of the positive electrode active material when the difference between the energy applied to the positive electrode active material and the energy applied to the reference material was the maximum was defined as the maximum exothermic peak temperature.
[0018]
DSC8230 (manufactured by Rigaku) was used for DSC measurement. The heating rate during the DSC measurement was 10 ° C./min. From the DSC measurement data, the total calorific value (kJ / g), the maximum exothermic peak output (W / g), and the maximum exothermic peak temperature (ΔC) when each composite oxide was used were read.
[0019]
(Production of battery)
As shown in FIG. 1, the positive and negative electrodes were wound around a shaft center 11 serving as a winding center through a polyolefin-based separator having a thickness of 40 μm so that these two electrodes did not come into direct contact with each other to form an electrode group 6. did. At this time, the lead pieces 9 of the positive electrode plate and the negative electrode plate were positioned on both end surfaces of the electrode group 6 on the opposite sides.
[0020]
The length of the negative electrode plate is set so that the positive electrode plate does not protrude from the negative electrode plate in the winding direction at the innermost circumference of the electrode group 6 and the positive electrode plate does not protrude from the negative electrode plate in the winding direction even at the outermost circumference. Was 18 cm longer than the length of the positive electrode plate. The width of the negative electrode active material application part was set to be 5 mm longer than the width of the positive electrode active material application part so that the positive electrode active material application part did not protrude from the negative electrode active material application part even in the direction perpendicular to the winding direction.
[0021]
The lead pieces 9 derived from the positive electrode plate were deformed, and all of them were gathered and brought into contact with the vicinity of the peripheral surface of the flange 7 integrally projecting from the periphery of the positive electrode external terminal 1 substantially on the extension of the shaft core 11. Thereafter, the lead piece 9 and the peripheral surface of the flange 7 were ultrasonically welded to connect the lead 9 to the peripheral surface of the flange 7 and fixed. The connection operation between the negative external terminal 1 ′ and the lead piece 9 derived from the negative electrode plate was performed in the same manner as the connection operation between the positive external terminal 1 and the lead piece 9 derived from the positive electrode plate.
[0022]
Thereafter, an insulating coating 8 was applied to the entire periphery of the flange 7 of the positive external terminal 1 and the negative external terminal 1 '. The insulating coating 8 extended over the entire outer peripheral surface of the electrode group 6. For the insulating coating 8, a pressure-sensitive adhesive tape was used in which the base material was polyimide and one side thereof was coated with a pressure-sensitive adhesive composed of hexamethacrylate. This adhesive tape was wound in multiple layers from the circumferential surface of the flange 7 to the outer circumferential surface of the electrode group 6 to form an insulating coating 8. The number of windings was adjusted so that the maximum diameter portion of the electrode group 6 was the portion where the insulating coating 8 was present, and was slightly smaller than the inner diameter of the cylindrical SUS battery container 5 having a diameter of 65 mm and a height of 390 mm. The group 6 is inserted into the battery container 5.
[0023]
Then, a second ceramic washer 3 ′ made of alumina and having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 25 mm at a portion in contact with the back surface of the disc-shaped battery lid 4 was used, and as shown in FIG. The pole and the tip were fitted into the pole and the pole constituting the negative electrode external terminal 1 ', respectively. A first ceramic washer 3 made of alumina and having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm is placed on the battery cover 4, and the positive external terminal 1 and the negative external terminal 1 ′ are respectively connected to the first ceramic. Passed through washer 3. Thereafter, the peripheral end face of the battery lid 4 was fitted into the opening of the battery container 5, and the entire area of both contact portions was laser-welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ penetrate a hole formed in the center of the battery cover 4 and protrude to the outside of the battery cover 4. Then, as shown in FIG. 1, a first ceramic washer 3 and a metal washer 14 smoother than the bottom surface of the metal nut 2 were fitted into the positive external terminal 1 and the negative external terminal 1 ′ in this order. The battery lid 4 is provided with a plate-shaped cleavage valve 10 made of an aluminum alloy that is cleaved in accordance with an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was about 9 × 10 ⁵ .
[0024]
Next, the nut 2 is screwed to each of the positive external terminal 1 and the negative external terminal 1 ′, and the battery cover 4 is connected to the flange 7 via the second ceramic washer 3 ′, the first ceramic washer 3, and the metal washer 14. It was fixed between nuts 2 by tightening. The tightening torque value at this time was 7 N · m. The metal washer 14 did not rotate until the tightening operation was completed. In this state, the compression of the rubber (EPDM) O-ring 16 interposed between the back surface of the battery lid 4 and the flange portion 7 shuts off the power generation element inside the battery container 5 from the outside air.
[0025]
Thereafter, a predetermined amount of the non-aqueous electrolyte prepared in the same manner as described above is injected into the battery container 5 from the liquid injection port 15 provided in the battery cover 4, and then the liquid injection port 15 is sealed to obtain a capacity of 90 Ah and output power. A cylindrical lithium ion secondary battery 20 of 1000 W or more was assembled.
[0026]
【Example】
Next, an example of the cylindrical lithium ion secondary battery 20 manufactured according to the present embodiment will be described. Note that a battery of a comparative example manufactured for comparison is also described.
[0027]
(Comparative Example 1)
As shown in Table 1 below, in Comparative Example 1, the positive electrode active material had a total heating value of 1.1 (kJ / g), a maximum heating peak output of 25 (W / g), and a maximum heating peak temperature of 280 (W / g). A battery was prepared using the composite oxide a of (C).
[0028]
[Table 1]

[0029]
(Comparative Example 2)
In Comparative Example 2, a battery was manufactured in the same manner as in Comparative Example 1, except that a composite oxide b having a maximum exothermic peak output of 13 (W / g) was used as the positive electrode active material.
[0030]
(Example 1)
Example 1 was the same as Comparative Example 1 except that a composite oxide c having a total heat generation of 1.0 (kJ / g) and a maximum heat generation peak output of 13 (W / g) was used as the positive electrode active material. To produce a battery.
[0031]
(Examples 2 to 4)
In Examples 2 to 4, the positive electrode active materials each had a total heat generation of 0.8 (kJ / g), a maximum heat generation peak temperature of 290 (° C), and a maximum heat generation peak output of 10, 9, 7 ( A battery was fabricated in the same manner as in Comparative Example 1, except that the composite oxides (W / g) were used.
[0032]
(Example 5)
In Example 5, a composite oxide g having a total heat generation of 0.8 (kJ / g), a maximum heat generation peak output of 7 (W / g), and a maximum heat generation peak temperature of 300 (° C) was used as the positive electrode active material. A battery was produced in the same manner as in Comparative Example 1, except that was used.
[0033]
(Comparative Examples 3 and 4)
In Comparative Example 3, a composite oxide h having a total heat generation of 1.3 (kJ / g), a maximum heat generation peak output of 28 (W / g), and a maximum heat generation peak temperature of 280 (° C) was used as the positive electrode active material. Was used to produce a battery. Comparative Example 4 was the same as Comparative Example 3 except that a composite oxide i having a total heat generation of 1.1 (kJ / g) and a maximum heat generation peak output of 15 (W / g) was used as the positive electrode active material. To produce a battery.
[0034]
(Example 6)
Example 6 was the same as Comparative Example 3 except that a composite oxide j having a total heat generation of 1.0 (kJ / g) and a maximum heat generation peak output of 15 (W / g) was used as the positive electrode active material. To produce a battery.
[0035]
(Examples 7 to 9)
In Examples 7 to 9, the positive electrode active materials had a total heat generation of 0.9, 0.8, 0.9 (kJ / g), a maximum heat generation peak output of 10, 9, 8 (W / g), respectively. A battery was produced in the same manner as in Comparative Example 3, except that the composite oxides k, l, and m having the maximum exothermic peak temperatures of 280, 290, and 280 (° C) were used.
[0036]
In Example 10, the composite oxide n having a total heat generation of 0.9 (kJ / g), a maximum heat generation peak output of 8 (W / g), and a maximum heat generation peak temperature of 300 (° C) was used as the positive electrode active material. A battery was fabricated in the same manner as in Comparative Example 3 except that was used.
[0037]
In the above Examples and Comparative Examples, the composite oxides a to g are lithium manganese composite oxides having a spinel structure, and the composite oxides hn are composite oxides having a layered structure containing lithium, manganese, cobalt and nickel. Things.
[0038]
<Test / Evaluation>
Next, for each of the batteries of the example and the comparative example manufactured as described above, an overcharge test in which a current of 0.5 C was continuously passed in the charging direction was performed, and the maximum temperature of the surface of the battery can 7 at this time was determined. It was measured. The status of ignition was also examined. Table 2 below shows the results of the maximum temperature measured and the presence or absence of ignition.
[0039]
[Table 2]

[0040]
As shown in Table 2, in the batteries of Examples in which the DSC of the lithium manganese composite oxide having a spinel structure had a total calorific value of 1.0 (kJ / g) or less, the ignition phenomenon at the time of overcharging was eliminated, and smoke was not generated. It erupted only. In the batteries of Examples 3 to 5 having a maximum heat generation peak output of 9 W / g or less, the degree of smoke emission became very gentle. Further, in the battery of Example 5 having a maximum heat generation peak temperature of 300 ° C. or more, the maximum temperature reached 115 ° C. on the battery surface could be lowered. Similarly, even with a positive electrode using a composite oxide having a layered structure containing lithium, manganese, cobalt, and nickel, the battery of the example in which the total calorific value of the DSC is 1.0 (kJ / g) or less causes ignition at the time of overcharge. The phenomena disappeared, and only the smoke spewed out. In the batteries of Examples 8 to 10 having a maximum heat generation peak output of 9 W / g or less, the degree of smoke emission became very gentle. Further, in the battery of Example 10 having a maximum heat generation peak temperature of 300 ° C. or more, the maximum temperature reached 125 ° C. on the battery surface could be lowered.
[0041]
From the above test results, a composite oxide having a total heat generation of 1.0 (kJ / g) or less, a maximum heat generation peak output of 9 (W / g) or less, and a maximum heat generation peak temperature of 300 (° C) or more was used as a positive electrode. The battery used as the active material was found to be excellent in safety.
[0042]
Note that, in the above embodiment, an example in which a lithium manganese composite oxide having a spinel structure was used as the positive electrode active material was described. However, the lithium site or manganese site of LiMn ₂ O ₄ was replaced with another metal element (eg, Li, Co). , Ni, Fe, Cu, Al, Cr, Mg, Zn, V, Ga, B, or F). Further, in the above embodiment, an example in which a composite oxide having a layered structure containing lithium, manganese, cobalt, and nickel is used, but a composite oxide having a layered structure substituted with another metal element is used. Is also good.
[0043]
Further, in the present embodiment, an example in which the mixing ratio of the positive electrode active material, the conductive material, and the binder is set to 90: 5: 5, but the mixing ratio is not limited to this, and for example, 85: 10: 5. It goes without saying that the present invention can be applied to such cases.
[0044]
Further, in the present embodiment, an example in which amorphous carbon is used as the negative electrode active material has been described. However, the present invention is not limited to this. Natural graphite capable of inserting and removing lithium ions, and various artificial graphites The material may be a carbonaceous material such as coke or coke, and the particle shape is not particularly limited, such as flakes, spheres, fibers, and lump.
[0045]
Furthermore, in the present embodiment, an example in which LiPF ₆ was used as the electrolyte, it is not limited thereto, for _{_{_{example, LiClO 4, LiAsF 6, LiBF}}} 4, LiB (C 6 H 5) 4, CH ₃ SO ₃ Li, CF ₃ SOLi, and the like, and a mixture thereof can be used. Further, in the present embodiment, an example in which a mixed solvent of EC and DMC is used as the solvent of the non-aqueous electrolyte has been described, but propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, , 2-diethoxyethane, γ-butyllactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, at least one such as propionitrile, propionitrile, etc. More than one kind of mixed solvent may be used, and the mixing ratio is not limited.
[0046]
Furthermore, in this embodiment, an example in which PVDF is used as the binder has been described, but polyethylene terephthalate, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethylcellulose Polymers such as various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and acrylic resins, and mixtures thereof can be used.
[0047]
Further, in the present embodiment, an example in which a cylindrical battery can is used for the battery container has been described. However, the present invention is not limited in terms of the shape of the battery, and may be a square battery, another polygon battery, or a stacked battery. Is also applicable.
[0048]
【The invention's effect】
As described above, according to the present invention, the positive electrode active material has a total amount of heat generated by a differential scanning calorimeter using a differential scanning calorimeter of 1.0 kJ / g or less, or a lithium-manganese composite oxide, or lithium, manganese, or cobalt. By using a composite oxide having a layered structure containing nickel and nickel, the total amount of heat generated by the composite oxide can be suppressed, so that a nonaqueous electrolyte secondary battery with excellent safety can be realized. The effect can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a cylindrical lithium ion secondary battery according to an embodiment to which the present invention can be applied.
[Explanation of symbols]
20 Cylindrical lithium ion secondary battery (lithium secondary battery)

Claims

In a lithium secondary battery in which a positive electrode using a lithium manganese composite oxide having a spinel structure as a positive electrode active material and a negative electrode using a carbon material as a negative electrode active material are immersed in a non-aqueous electrolyte, the lithium manganese composite oxide A lithium secondary battery, wherein the total amount of heat generated by the object by a differential scanning calorimeter is 1.0 kJ / g or less.

The lithium secondary battery according to claim 1, wherein the maximum exothermic peak output of the lithium manganese composite oxide measured by a differential scanning calorimeter is 9 W / g or less.

The lithium secondary battery according to claim 1, wherein a maximum exothermic peak temperature of the lithium manganese composite oxide measured by a differential scanning calorimeter is 300 ° C. or higher.

In a lithium secondary battery in which a positive electrode using a layered structure composite oxide containing lithium, manganese, cobalt and nickel as a positive electrode active material and a negative electrode using a carbon material as a negative electrode active material are infiltrated into a non-aqueous electrolyte. A total amount of heat generated by the differential scanning calorimeter of the composite oxide is 1.0 kJ / g or less.

The lithium secondary battery according to claim 4, wherein the composite oxide has a maximum exothermic peak output by a differential scanning calorimeter of 9 W / g or less.

The lithium secondary battery according to claim 4, wherein a maximum exothermic peak temperature of the composite oxide measured by a differential scanning calorimeter is 300 ° C. or higher.