JP4711479B2

JP4711479B2 - Honeycomb structure current collector for electrode of lithium ion secondary battery, electrode for lithium ion secondary battery, and method for producing honeycomb structure current collector for electrode of lithium ion secondary battery

Info

Publication number: JP4711479B2
Application number: JP30566699A
Authority: JP
Inventors: 和靖中根; 幸三杉山
Original assignee: Inoac Corp; Japan Science and Technology Agency; Inoac Technical Center Co Ltd; National Institute of Japan Science and Technology Agency
Current assignee: Inoac Corp; Japan Science and Technology Agency; Inoac Technical Center Co Ltd; National Institute of Japan Science and Technology Agency
Priority date: 1999-10-27
Filing date: 1999-10-27
Publication date: 2011-06-29
Anticipated expiration: 2019-10-27
Also published as: JP2001126736A

Description

【０００１】
【発明の属する技術分野】
この発明はリチウムイオン二次電池の電極用ハニカム構造集電体、リチウムイオン二次電池の電極及びリチウムイオン二次電池の電極用ハニカム構造集電体の製造方法に関する。
【０００２】
【従来の技術】
近年、ノートパソコン、携帯電話、携帯ビデオカメラ等の電子機器における高機能化や小型化に伴い、小型で高容量の二次電池が要求されるようになり、それに応えるものとして、リチウムイオン二次電池が多用されている。
【０００３】
このリチウムイオン二次電池は、図９に示すように、二酸化コバルト（ＣｏＯ_２）やコバルト酸リチウム（Ｌｉ_ｘＣｏＯ_２）の粉末または高価なコバルトを一部他の金属で置き換えた粉末からなる正極用活物質５１を、アルミニウム箔等の金属箔やメッシュ等からなる集電体５２に導電性塗料（バインダー）とともに塗布した構成のシート状正極５３と、黒鉛化炭素、非晶質炭素などの粉末あるいは黒鉛化炭素繊維からなる負極用活物質６１を、銅箔等からなる集電体６２に導電性塗料（バインダー）とともに塗布した構成のシート状負極６３とを、多孔質膜等からなるセパレータＳを介して積層し、その積層体を電解液とともに電池ケース内に収納したものが一般的である。なお、円筒型リチウムイオン二次電池にあっては、前記正極、セパレータ及び負極からなる積層体が渦状に巻かれて、電解液とともに外装缶に収納されている。電解液はセパレータに含浸したものとされることもある。
【０００４】
【発明が解決しようとする課題】
ところで、前記ノートパソコン、携帯電話、携帯ビデオカメラ等は、さらなる高機能化及び長時間連続使用が求められており、それに応じてリチウムイオン二次電池も一層高容量のものが必要になっている。
【０００５】
前記リチウムイオン二次電池を高容量化するには、有効な活物質の量を増大させる必要がある。しかし、前記構造にあっては活物質層の厚み（塗布厚）を増そうとしても、塗布によってはそれほど厚く活物質を金属箔（集電体）表面に付着できず、たとえ金属箔表面に厚く付着できたとしても、活物質の厚みが大になるほど金属箔から活物質が剥離し易くなるので、活物質の厚み、すなわち有効な活物質の量に制限があり、高容量化が難しかった。
【０００６】
この発明は前記の点に鑑みなされたものであって、軽量性を損なうことなく、しかも大容量化が可能なリチウムイオン二次電池の電極用ハニカム構造集電体、リチウムイオン二次電池の電極及びリチウムイオン二次電池の電極用ハニカム構造集電体の製造方法を提供するものである。
【０００７】
【課題を解決するための手段】
請求項１に係る発明は、炭素質ハニカム構造体の外表面を含むセルの隔壁表面に窒化チタン膜を被着し、炭素質ハニカム構造体のセル径ｄが５００〜７００μｍであることを特徴とするリチウムイオン二次電池の電極用ハニカム構造集電体に係る。
【０００８】
この請求項１の発明によれば、集電体は、ハニカム構造からなるため、軽量で強度が高い。また、ハニカム構造集電体の断面におけるセルの積層数（段数）を増やしても充分な集電体の強度を維持できる。しかも、ハニカム構造のセル内に正極用または負極用活物質を充填するようにすれば、セルの積層数を増加させることによって活物質の総充填量を増大させることができ、個々のセルサイズを大きくする必要がないため、集電体の強度低下を生じることなく活物質の充填量を増大させ、リチウムイオン二次電池の高容量化を図ることができる。さらに、セルの積層数の増加によって活物質の総充填量を増大させても、活物質は各セル内に保持されるため、活物質を金属箔状集電体に厚く塗布する場合に生じる活物質の剥離や脱落等を防ぐことができる。
【０００９】
請求項２に係る発明は、請求項１のハニカム構造集電体のセル内に正極用又は負極用活物質を充填し、ハニカム構造体のセル径ｄが５００〜７００μｍであることを特徴とするリチウムイオン二次電池の電極に係る。
【００１０】
この請求項２の発明によれば、軽量で強度の高いハニカム構造集電体のセル内に正極用又は負極用活物質を充填するため、軽量な電極が得られる。しかも、セル内に活物質が充填されるため、セルの積層数を増やして活物質の総充填量の増大を図っても、活物質の剥離や脱落の恐れがなく、リチウムイオン二次電池の高容量化を実現することができる。
【００１１】
請求項３に係る発明は、正極用又は負極用活物質がハニカム構造のセル内に充填されるリチウムイオン二次電池の電極用集電体の製造に際し、熱分解によって炭化する有機質シート材料から形成したハニカム状成形体を非酸化性雰囲気中で燻焼炭化してセル径ｄが５００〜７００μｍである炭素質ハニカム構造体を形成し、前記炭素質ハニカム構造体を気相反応装置内に置き、化学反応により窒化チタンを生成する原料ガスを７５０〜１１００℃で前記気相反応装置内に数千回以上のパルスとして供給・排気を繰り返すことにより、当該炭素質ハニカム構造体の外表面を含むセルの隔壁表面に窒化チタン膜を被着させることを特徴とするリチウムイオン二次電池の電極用ハニカム構造集電体の製造方法に係る。
【００１２】
この請求項３の発明によれば、有機質シート材料は軟質で糊付けもできるので、波型状の成形、平板状シートとの重ね合わせ、渦巻き成形などが容易であり、各種の市販段ボールを渦巻き状に巻いて用いることもでき、ハニカム構造からなる所望の集電体を容易に得ることができる。しかも、有機質シート材料から形成したハニカム状成形体を非酸化性雰囲気中で燻焼炭化した炭素質ハニカム構造体は、軽量なため、それによってリチウムイオン二次電池の電極も軽量にすることができる。
【００１３】
【発明の実施の形態】
以下この発明を詳細に説明する。図１はこの発明に係るリチウムイオン二次電池の電極用ハニカム構造集電体の一実施例における概略斜視図、図２は図１の部分拡大断面図、図３は図１の集電体を用いたリチウムイオン二次電池用電極の一実施例の概略斜視図、図４は図３の部分拡大断面図、図５はこの発明の集電体の製造に用いる装置の一実施例の配置説明図、図６は実施例によって得られた炭素質ハニカム構造体のＳＥＭ観察による平均的な微構造の概略図、図７は充放電特性曲線、図８は放電量曲線である。
【００１４】
図１及びその部分拡大図である図２に示すリチウムイオン二次電池の電極用ハニカム構造集電体１０は、炭素質ハニカム構造体１１の外表面を含むセル１２の隔壁１３表面に窒化チタン膜１５を被着した構造からなる。
【００１５】
炭素質ハニカム構造体１１は、集電体１０の骨格（基材）をなすもので、セル（孔）１２が多数形成されたハニカム構造からなる。この炭素質ハニカム構造体１１は、有機質シート材料からなるシート状のハニカム状成形体を、非酸化性雰囲気中で燻焼炭化したもので、原形状のハニカム形状をいくらか収縮して継承した形状からなる。有機質シート材料としては、熱分解により原型状を維持して炭化するものが用いられ、セルローズ系薄紙、熱硬化性樹脂系の繊維紙又はフィルムなどを挙げることができる。また、有機質シート材料からなるハニカム状成形体としては、前記有機質シート材料を糊などを用いて所望の段数、形状、大きさからなるハニカム状に成形したものであり、簡単には市販の段ボールを用いることもできる。なお、炭素質ハニカム構造体１１の外形は平板状等、適宜の形状とされる。セル１２の形状は、三角形、円形、四角形等、あるいはそれらの崩れた形状からなるものであってもよい。さらに、セル１２のサイズやセルの隔壁１３厚みは適宜とされるが、例としてセル１２の開口径（円径の場合は直径、三角形の場合はその最長辺）が１ｍｍ以下、隔壁１３厚みが２０μｍ以下を挙げる。
【００１６】
窒化チタン膜１５は、集電体としての充分な表面導電性を確保するためのものであって、前記炭素質ハニカム構造体１１の外表面１１ａを含むセル１２の隔壁１３表面、すなわち炭素質ハニカム構造体１１の全表面に積層されている。その窒化チタン膜１５の形成は、前記炭素質ハニカム構造体１１を気相反応装置内に置き、化学反応により窒化チタンを生成する原料ガスを７５０〜１１００℃で前記気相反応装置内に間欠的に、具体的には数千回以上のパルスとして供給・排気を繰り返すことによりなされる。
【００１７】
前記窒化チタンを生成する原料ガスとしては、四塩化チタン（ＴｉＣｌ_４）、窒素及び水素の混合ガスを使用し、ガスの組成は例えば四塩化チタン１〜１５％（モル％。以下同じ。）、窒素５〜５０％、水素３５〜９４％が使用可能であり、特に四塩化チタン４〜８％、窒素１０〜４０％、水素５２〜８６％の混合ガスが実際上望ましい。なお、原料ガスとして窒素の代わりにアンモニア（ＮＨ_３）も使用することができる。
【００１８】
反応温度は、炭素質ハニカム構造体１１におけるセル１２のサイズや隔壁１３の厚み等を考慮して選択されるが、一般に高温になるほど窒化チタンの蒸着速度が増大し、窒化チタンが隔壁１３表面に析出し易くなって、微細な部分へのガスの供給が妨げられるようになり、また低温では蒸着速度が低下して長時間の処理が必要になる。それらの観点から、反応温度は７５０〜１１００℃が好ましく、特には７８０〜９５０℃の範囲が窒化チタンの性質及び効率の点から望ましい。
【００１９】
前記原料ガスの間欠的供給（パルスとしての供給）は、真空吸引された反応容器（反応装置）内に瞬間的に行われる。それにより、炭素質ハニカム構造体１１のセル１２内が新鮮な原料ガスによって瞬間的に常圧まで満たされるから、一度に多数の炭素質ハニカム構造体１１を反応容器内に収容しても、全ての炭素質ハニカム構造体に対して窒化チタンの析出が均一になされる。実際には、反応容器への原料ガスの瞬間的導入工程、所要時間原料ガスを保持して蒸着を行う工程、及び反応容器内から残留未反応原料ガスと反応生成する塩化水素ガスの真空吸引工程の３工程を１サイクルとする、極めて短時間のパルスを繰り返す必要がある。１サイクル内の工程の切り替えは、反応容器に通じる経路に設けた電磁弁を、予め設定したプログラムにしたがって開閉制御することにより行われる。
【００２０】
前記反応容器内への原料ガスの常圧までの瞬間的導入は０．１秒以内に完了するが、反応析出のための保持時間は反応温度により調節する必要があり、温度が高いときは０．３秒程度の短時間で充分であるのに対し、温度が低いときは２秒程度まで長くするのが望ましい。次の排気に要する時間は、５Ｔｏｒｒ以下の圧力状態までガスを除去することを目安とし、吸熱反応により炭素質ハニカム構造体１１の温度が一時的に低下するので、反応容器中に一度に多数の炭素質ハニカム構造体１１が収容されているときは、炭素質ハニカム構造体１１が、基準とする温度まで回復するためにも時間が必要となる。これらを考慮し、真空吸引の時間は一般に０．３〜２秒の範囲で設定される。これにより、１パルス当たりの所要時間は１．４〜４．０秒となる。
【００２１】
なお、前記１回のパルスで炭素質ハニカム構造体１１に被着する窒化チタンの量は極めて僅かなため、電気的導通を保証するには数千回以上、好ましくは８０００〜１５０００回のパルスが必要である。
【００２２】
また、図３及びその部分拡大断面図である図４に示すリチウムイオン二次電池用電極２０は、前記集電体１０のセル１２内に活物質２１を充填したものであって、活物質２１が正極用活物質であれば正極となり、それに対して活物質２１が負極活物質であれば負極となる。活物質２１がセル１２内に充填されるため、剥離や落下を生じず、またセル１２の数を増やすことにより容易に活物質２１の量を増やすことができる。それにより、高容量のリチウムイオン二次電池を得ることができるようになる。
【００２３】
正極用活物質としては、二酸化コバルト（ＣｏＯ_２）やコバルト酸リチウム（Ｌｉ_ｘＣｏＯ_２）の粉末またはコバルトを一部他の金属で置き換えた粉末などからなる公知のものが用いられ、また負極用活物質としては、黒鉛化炭素、非晶質炭素などの粉末あるいは黒鉛化炭素繊維からなる公知のものが用いられる。それらの活物質２１は、溶媒及びバインダーと混合されて前記セル１２内に充填され、真空で乾燥される。真空乾燥は、減圧ポンプが連動した公知の真空乾燥炉を用いて２００〜２２０℃の温度で行われる。
【００２４】
【実施例】
以下実験室的な具体的な実施例について説明する。実際の製造では、装置等の規模を数百倍に拡大したものを使用できる。また、図５の装置では高温炉２の炉内雰囲気制御のため、炉中に石英ガラス製反応器１を挿入する方法を採ったが、大型の真空雰囲気炉を直接使用することも可能である。符号４は真空ポンプ、５は電磁弁ある。
【００２５】
まず、市販の片段段ボール（コルゲートの山の高さ１ｍｍのもの）を平面寸法２５×２５ｍｍにし、接着剤（ゴム糊）を介して１５段積層し、接着乾燥させた。その段ボール積層品をアルゴン雰囲気中で１０００℃、４時間炭化処理し、２０×１０×２０ｍｍの炭素質ハニカム構造体を得た。この炭素質ハニカム構造体に対し、ＳＥＭ観察を行った。図６は、その平均的な微細構造を示すものであり、セル１２の径ｄが５００〜７００μｍ、隔壁１３の厚みが約１０μｍ、全体の空隙率が約９０％であった。
【００２６】
このようにして得られた炭素質ハニカム構造体１１を気相反応容器（装置）１内に固定し、電気炉２を８５０℃に昇温し、水素１５モル％を四塩化チタン飽和器７を通過させ、四塩化チタン濃度１．５％、水素６３．５％、窒素３５％の原料ガスにしてリザーバータンク６に蓄え、これから反応容器１内に圧力パルスとして供給し、１００００パルスまでこれを行ない、集電体１０を得た。このようにして得られた集電体１０の電気抵抗率は、窒化チタン膜被着前の炭素質ハニカム構造体１１の電気抵抗率が約０．１０Ωｃｍであったのに対し、約５０μΩｃｍであった。
【００２７】
前記集電体１０に対し、負極のみの評価を行った。その作製方法は、黒鉛粉末（ＭＣＭＢ；大阪ガスケミカル社製）５５重量部と、溶媒（Ｎ−メチル−２−ピロリドン；キシダ化学社製）２２．５重量部と、バインダー（ＫＦポリマーＬ＃１１２０；呉羽化学工業社製）２２．５重量部とを混合して得た負極用ペーストを、それぞれ指圧により集電体１０のセル内に充填した。次いで真空管走路内に収容し、２００℃で７２時間真空乾燥し、リチウムイオン電池負極を得た。
【００２８】
前記リチウムイオン二次電池の負極に対し、それぞれ３極セルで充放電を行った。その結果を図７の充放電特性曲線、図８の放電量曲線で表す。３極セルにおける参照極と対象極にはリチウム箔、電解液には、１：１のＥＣ（エチレンカーボネート）とＤＥＣ（ジエチレンカーボネート）からなる電解溶媒（三菱化学社製）に電解質としてＬｉＣｌ_４を溶解した１ｍｏｌ／ｌのＬｉＣｌ_４／（ＥＣ＋ＤＥＣ）を用いた。
【００２９】
【発明の効果】
以上図示し説明したように、請求項１の発明によれば、集電体は、ハニカム構造からなるため、軽量で強度が高いものとなる。しかも、セル内を正極用または負極用活物質の充填場所とできるため、活物質を集電体から剥離等なく保持することができるようになる。また、ハニカム構造集電体の断面におけるセルの積層数（段数）を増やしても充分な集電体の強度を維持できるため、セルの積層数を増加させることによって活物質の総充填量を増大させることができ、個々のセルサイズを大きくする必要がないため、集電体の強度低下を生じることなく活物質の充填量を増大させ、リチウムイオン二次電池の高容量化を図ることができる。さらに、セルの積層数の増加によって活物質の総充填量を増大させても、活物質は各セル内に保持されるため、活物質を金属箔状集電体に厚く塗布する場合に生じる活物質の剥離や脱落等を防ぐことができる。
【００３０】
また、請求項２の発明によれば、軽量で強度の高いハニカム構造集電体のセル内に正極用又は負極用活物質を充填するため、軽量な電極が得られる。しかも、セル内に活物質が充填されるため、セルの積層数を増やして活物質の総充填量の増大を図っても、活物質の剥離や脱落の恐れがなく、リチウムイオン二次電池の高容量化を実現することができる。
【００３１】
さらに請求項３の発明によれば、ハニカム状成形体を構成する有機質シート材料は軟質で糊付けも可能なため、波型状の成形、平板状シートとの重ね合わせ、渦巻き成形などが容易であり、各種の、市販の段ボールを渦巻き状に巻いて用いることもでき、ハニカム構造からなる所望の集電体を容易に得ることができる。しかも、有機質シート材料から形成したハニカム状成形体を非酸化性雰囲気中で燻焼炭化した炭素質ハニカム構造体は、軽量なため、それによってリチウムイオン二次電池の電極も軽量にすることができる。
【図面の簡単な説明】
【図１】この発明に係るリチウムイオン二次電池の電極用ハニカム構造集電体の一実施例における概略斜視図である。
【図２】図１の部分拡大断面図である。
【図３】図１の集電体を用いたリチウムイオン二次電池用電極の一実施例の概略斜視図である。
【図４】図３の部分拡大断面図である。
【図５】この発明の集電体の製造に用いる装置の一実施例の配置説明図である。
【図６】実施例によって得られた炭素質ハニカム構造体のＳＥＭ観察による平均的な微構造の概略図である。
【図７】充放電特性曲線である。
【図８】放電量曲線である。
【図９】従来のリチウムイオン二次電池の構造を示す概略図である。
【符号の説明】
１０集電体
１１炭素質ハニカム構造体
１２セル
１３隔壁
１５窒化チタン膜
２０電極
２１活物質[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a honeycomb structure current collector for an electrode of a lithium ion secondary battery, an electrode of a lithium ion secondary battery, and a method for manufacturing a honeycomb structure current collector for an electrode of a lithium ion secondary battery.
[0002]
[Prior art]
In recent years, as electronic devices such as notebook computers, mobile phones, and portable video cameras have become more sophisticated and smaller, there has been a demand for small, high-capacity secondary batteries. Batteries are frequently used.
[0003]
As shown in FIG. 9, this lithium ion secondary battery is a positive electrode comprising a powder of cobalt dioxide (CoO ₂ ) or lithium cobaltate (Li _x CoO ₂ ) or a powder in which expensive cobalt is partially replaced with another metal. Sheet-like positive electrode 53 having a configuration in which active material 51 is applied to a current collector 52 made of a metal foil such as aluminum foil or a mesh together with a conductive paint (binder), and powders such as graphitized carbon and amorphous carbon Alternatively, a sheet-like negative electrode 63 having a structure in which a negative electrode active material 61 made of graphitized carbon fiber is applied to a current collector 62 made of copper foil or the like together with a conductive paint (binder), and a separator S made of a porous film or the like. In general, the laminated body is housed in a battery case together with an electrolytic solution. In the cylindrical lithium ion secondary battery, the laminate composed of the positive electrode, the separator, and the negative electrode is wound in a spiral shape and stored in an outer can together with the electrolytic solution. The electrolyte may be impregnated in the separator.
[0004]
[Problems to be solved by the invention]
By the way, the above-mentioned notebook personal computers, mobile phones, mobile video cameras, etc. are required to have higher functionality and continuous use for a long time, and accordingly, lithium ion secondary batteries are required to have higher capacities. .
[0005]
In order to increase the capacity of the lithium ion secondary battery, it is necessary to increase the amount of effective active material. However, in the above structure, even if the thickness of the active material layer (coating thickness) is increased, the active material cannot be deposited so thickly on the surface of the metal foil (current collector) depending on the coating, even if it is thick on the surface of the metal foil. Even if it can be adhered, the active material is more easily peeled off from the metal foil as the thickness of the active material is increased. Therefore, the thickness of the active material, that is, the amount of effective active material is limited, and it is difficult to increase the capacity.
[0006]
The present invention has been made in view of the above-described points, and has a honeycomb structure current collector for an electrode of a lithium ion secondary battery capable of increasing the capacity without impairing lightness, and an electrode of the lithium ion secondary battery And the manufacturing method of the honeycomb structure electrical power collector for electrodes of a lithium ion secondary battery is provided.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is characterized in that a titanium nitride film is deposited on the partition wall surface of the cell including the outer surface of the carbonaceous honeycomb structure, and the cell diameter d of the carbonaceous honeycomb structure is 500 to 700 μm. The present invention relates to a honeycomb structure current collector for an electrode of a lithium ion secondary battery.
[0008]
According to the first aspect of the present invention, since the current collector has a honeycomb structure, it is lightweight and has high strength. Moreover, even if the number of stacked cells (number of steps) in the cross section of the honeycomb structure current collector is increased, sufficient strength of the current collector can be maintained. In addition, if the positive electrode or negative electrode active material is filled in the cells of the honeycomb structure, the total filling amount of the active material can be increased by increasing the number of stacked cells, and the individual cell size can be increased. Since it is not necessary to increase the capacity, the filling amount of the active material can be increased without reducing the strength of the current collector, and the capacity of the lithium ion secondary battery can be increased. Furthermore, even if the total filling amount of the active material is increased by increasing the number of stacked cells, the active material is retained in each cell. Therefore, the active material generated when the active material is applied thickly to the metal foil current collector. It is possible to prevent the material from peeling off or falling off.
[0009]
The invention according to claim 2 is characterized in that the cells of the honeycomb structure current collector of claim 1 are filled with an active material for a positive electrode or a negative electrode, and the cell diameter d of the honeycomb structure is 500 to 700 μm. The present invention relates to an electrode of a lithium ion secondary battery.
[0010]
According to the second aspect of the present invention, since the active material for positive electrode or negative electrode is filled in the cells of the honeycomb structure current collector having light weight and high strength, a light electrode can be obtained. Moreover, since the active material is filled in the cell, there is no risk of the active material peeling or dropping even if the number of stacked cells is increased to increase the total amount of the active material. High capacity can be realized.
[0011]
The invention according to claim 3 is formed from an organic sheet material that is carbonized by thermal decomposition in the production of a current collector for an electrode of a lithium ion secondary battery in which a positive electrode or negative electrode active material is filled in a honeycomb structure cell. The carbonaceous honeycomb structure having a cell diameter d of 500 to 700 μm is formed by calcination carbonization in a non-oxidizing atmosphere, and the carbonaceous honeycomb structure is placed in a gas phase reactor. A cell containing the outer surface of the carbonaceous honeycomb structure is obtained by repeatedly supplying and exhausting a source gas for generating titanium nitride by chemical reaction as a pulse of several thousand times or more at 750 to 1100 ° C. The present invention relates to a method for manufacturing a honeycomb structure current collector for an electrode of a lithium ion secondary battery, wherein a titanium nitride film is deposited on the surface of the partition wall.
[0012]
According to the invention of claim 3, since the organic sheet material is soft and can be glued, corrugated molding, superposition with a flat sheet, spiral molding and the like are easy, and various commercially available corrugated cardboards are spirally shaped. The desired current collector having a honeycomb structure can be easily obtained. Moreover, since the carbonaceous honeycomb structure obtained by calcination and carbonization of a honeycomb-shaped formed body made of an organic sheet material in a non-oxidizing atmosphere is lightweight, the electrode of the lithium ion secondary battery can also be lightened. .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below. 1 is a schematic perspective view of an embodiment of a honeycomb structure current collector for an electrode of a lithium ion secondary battery according to the present invention, FIG. 2 is a partially enlarged cross-sectional view of FIG. 1, and FIG. 3 is a view of the current collector of FIG. FIG. 4 is a partially enlarged cross-sectional view of FIG. 3, and FIG. 5 is a layout explanation of an embodiment of an apparatus used for manufacturing the current collector of the present invention. FIG. 6, FIG. 6 is a schematic diagram of an average microstructure by SEM observation of the carbonaceous honeycomb structure obtained by the example, FIG. 7 is a charge / discharge characteristic curve, and FIG. 8 is a discharge amount curve.
[0014]
A honeycomb structure current collector 10 for an electrode of a lithium ion secondary battery shown in FIG. 1 and FIG. 2 which is a partially enlarged view thereof has a titanium nitride film on the surface of the partition wall 13 of the cell 12 including the outer surface of the carbonaceous honeycomb structure 11. 15 is applied.
[0015]
The carbonaceous honeycomb structure 11 forms a skeleton (base material) of the current collector 10 and has a honeycomb structure in which a large number of cells (holes) 12 are formed. This carbon honeycomb structure 11 is obtained by calcining and carbonizing a sheet-like honeycomb formed body made of an organic sheet material in a non-oxidizing atmosphere. Become. As the organic sheet material, a material that is carbonized while maintaining its original shape by pyrolysis is used, and examples thereof include cellulose thin paper, thermosetting resin fiber paper, or a film. In addition, as a honeycomb-shaped formed body made of an organic sheet material, the organic sheet material is formed into a honeycomb shape having a desired number of steps, shape, and size using glue or the like. It can also be used. The outer shape of the carbonaceous honeycomb structure 11 is an appropriate shape such as a flat plate. The shape of the cell 12 may be a triangle, a circle, a quadrangle, or the like, or a broken shape thereof. Further, the size of the cell 12 and the thickness of the partition wall 13 of the cell are appropriately determined. For example, the opening diameter of the cell 12 (diameter in the case of a circle diameter, the longest side in the case of a triangle) is 1 mm or less, and the partition wall 13 thickness is List 20 μm or less.
[0016]
The titanium nitride film 15 is for ensuring sufficient surface conductivity as a current collector, and the surface of the partition wall 13 of the cell 12 including the outer surface 11a of the carbonaceous honeycomb structure 11, that is, the carbonaceous honeycomb. It is laminated on the entire surface of the structure 11. The titanium nitride film 15 is formed by placing the carbonaceous honeycomb structure 11 in a gas phase reactor and intermittently supplying a raw material gas for generating titanium nitride by a chemical reaction at 750 to 1100 ° C. in the gas phase reactor. Specifically, it is done by repeating supply and exhaust as pulses of several thousand times or more.
[0017]
As the raw material gas for producing the titanium nitride, a mixed gas of titanium tetrachloride (TiCl ₄ ), nitrogen and hydrogen is used, and the composition of the gas is, for example, 1 to 15% (mol%; the same applies hereinafter) of titanium tetrachloride. Nitrogen 5-50% and hydrogen 35-94% can be used. In particular, a mixed gas of titanium tetrachloride 4-8%, nitrogen 10-40% and hydrogen 52-86% is practically desirable. In addition, ammonia (NH ₃ ) can also be used as a raw material gas instead of nitrogen.
[0018]
The reaction temperature is selected in consideration of the size of the cells 12 in the carbonaceous honeycomb structure 11 and the thickness of the partition walls 13. In general, the higher the temperature, the higher the deposition rate of titanium nitride, and the titanium nitride is deposited on the surfaces of the partition walls 13. It becomes easy to precipitate, and the supply of the gas to the fine part is hindered. Further, at a low temperature, the deposition rate is lowered and a long time treatment is required. From these viewpoints, the reaction temperature is preferably 750 to 1100 ° C., and particularly in the range of 780 to 950 ° C. is desirable from the viewpoint of the properties and efficiency of titanium nitride.
[0019]
The supply of the source gas intermittently (supply as a pulse) is instantaneously performed in a vacuum-evacuated reaction vessel (reaction apparatus). Thereby, since the inside of the cells 12 of the carbonaceous honeycomb structure 11 is instantaneously filled with fresh raw material gas to normal pressure, even if a large number of carbonaceous honeycomb structures 11 are accommodated in the reaction vessel at once, Titanium nitride is uniformly deposited on the carbonaceous honeycomb structure. Actually, the step of instantaneously introducing the source gas into the reaction vessel, the step of performing deposition while holding the source gas for the required time, and the step of vacuum suction of hydrogen chloride gas generated by reaction with the residual unreacted source gas from the reaction vessel It is necessary to repeat an extremely short time pulse, with these three steps as one cycle. Switching between processes within one cycle is performed by opening and closing a solenoid valve provided in a path leading to the reaction vessel according to a preset program.
[0020]
The instantaneous introduction of the source gas into the reaction vessel up to the normal pressure is completed within 0.1 seconds, but the holding time for the reaction precipitation needs to be adjusted by the reaction temperature, and is 0 when the temperature is high. A short time of about 3 seconds is sufficient, but when the temperature is low, it is desirable to increase the time to about 2 seconds. The time required for the next exhaust is to remove the gas to a pressure state of 5 Torr or less, and the temperature of the carbonaceous honeycomb structure 11 is temporarily lowered by the endothermic reaction. When the carbonaceous honeycomb structure 11 is accommodated, time is required for the carbonaceous honeycomb structure 11 to recover to the reference temperature. Considering these, the vacuum suction time is generally set in the range of 0.3 to 2 seconds. As a result, the required time per pulse is 1.4 to 4.0 seconds.
[0021]
The amount of titanium nitride deposited on the carbonaceous honeycomb structure 11 in one pulse is very small, so that several thousand times or more, preferably 8000 to 15000 pulses are required to ensure electrical continuity. is necessary.
[0022]
3 and FIG. 4 which is a partially enlarged cross-sectional view thereof, the lithium ion secondary battery electrode 20 is obtained by filling the active material 21 in the cell 12 of the current collector 10. If it is an active material for positive electrodes, it will become a positive electrode, and if the active material 21 is a negative electrode active material, it will become a negative electrode. Since the active material 21 is filled in the cell 12, peeling or dropping does not occur, and the amount of the active material 21 can be easily increased by increasing the number of the cells 12. As a result, a high-capacity lithium ion secondary battery can be obtained.
[0023]
As the positive electrode active material, a known material made of a powder of cobalt dioxide (CoO ₂ ) or lithium cobaltate (Li _x CoO ₂ ) or a powder in which cobalt is partially replaced with another metal is used. As the active material, a known material made of powder of graphitized carbon or amorphous carbon or graphitized carbon fiber is used. These active materials 21 are mixed with a solvent and a binder, filled in the cell 12, and dried in a vacuum. The vacuum drying is performed at a temperature of 200 to 220 ° C. using a known vacuum drying furnace in which a vacuum pump is linked.
[0024]
【Example】
A specific laboratory example will be described below. In actual manufacturing, an apparatus or the like whose scale is increased several hundred times can be used. Further, in the apparatus of FIG. 5, a method of inserting the quartz glass reactor 1 into the furnace is adopted for controlling the atmosphere inside the high temperature furnace 2, but a large vacuum atmosphere furnace can also be directly used. . Reference numeral 4 is a vacuum pump, and 5 is a solenoid valve.
[0025]
First, a commercially available single-stage cardboard (one with a corrugated ridge height of 1 mm) was made to have a planar size of 25 × 25 mm, laminated in 15 stages via an adhesive (rubber glue), and dried. The corrugated board laminate was carbonized in an argon atmosphere at 1000 ° C. for 4 hours to obtain a carbon honeycomb structure having a size of 20 × 10 × 20 mm. SEM observation was performed on this carbonaceous honeycomb structure. FIG. 6 shows the average microstructure. The diameter d of the cell 12 is 500 to 700 μm, the thickness of the partition wall 13 is about 10 μm, and the overall porosity is about 90%.
[0026]
The carbonaceous honeycomb structure 11 thus obtained is fixed in a gas phase reaction vessel (apparatus) 1, the electric furnace 2 is heated to 850 ° C., and 15 mol% of hydrogen is supplied to a titanium tetrachloride saturator 7. Passed through and stored in the reservoir tank 6 as a raw material gas having a titanium tetrachloride concentration of 1.5%, hydrogen of 63.5%, and nitrogen of 35%, and then supplied as a pressure pulse into the reaction vessel 1 and up to 10,000 pulses. The current collector 10 was obtained. The electrical resistivity of the current collector 10 thus obtained was about 50 μΩcm, compared to about 0.10 Ωcm for the carbonaceous honeycomb structure 11 before deposition of the titanium nitride film. It was.
[0027]
For the current collector 10, only the negative electrode was evaluated. The production method is as follows: graphite powder (MCMB; manufactured by Osaka Gas Chemical Co., Ltd.) 55 parts by weight, solvent (N-methyl-2-pyrrolidone; manufactured by Kishida Chemical Co., Ltd.) 22.5 parts by weight, and binder (KF polymer L # 1120). A paste for negative electrode obtained by mixing 22.5 parts by weight of Kureha Chemical Industry Co., Ltd., was filled into the cells of the current collector 10 by finger pressure. Subsequently, it accommodated in a vacuum tube runway, and vacuum-dried at 200 degreeC for 72 hours, and the lithium ion battery negative electrode was obtained.
[0028]
The negative electrode of the lithium ion secondary battery was charged and discharged with a tripolar cell. The result is represented by the charge / discharge characteristic curve of FIG. 7 and the discharge amount curve of FIG. Lithium foil is used for the reference electrode and the target electrode in the three-electrode cell, and LiCl ₄ is used as an electrolyte in an electrolytic solvent (manufactured by Mitsubishi Chemical Corporation) made of 1: 1 EC (ethylene carbonate) and DEC (diethylene carbonate). Dissolved 1 mol / l LiCl ₄ / (EC + DEC) was used.
[0029]
【The invention's effect】
As illustrated and described above, according to the first aspect of the present invention, the current collector has a honeycomb structure, so it is lightweight and has high strength. In addition, since the inside of the cell can be filled with a positive electrode or negative electrode active material, the active material can be held from the current collector without peeling. In addition, even if the number of stacked cells (stages) in the cross section of the honeycomb structure current collector is increased, sufficient current collector strength can be maintained, so increasing the number of stacked cells increases the total active material filling amount. Since there is no need to increase the size of each cell, the filling amount of the active material can be increased without reducing the strength of the current collector, and the capacity of the lithium ion secondary battery can be increased. . Furthermore, even if the total filling amount of the active material is increased by increasing the number of stacked cells, the active material is retained in each cell. Therefore, the active material generated when the active material is applied thickly to the metal foil current collector. It is possible to prevent the material from peeling off or falling off.
[0030]
In addition, according to the invention of claim 2, since the positive electrode or negative electrode active material is filled in the cells of the lightweight and high strength honeycomb structure current collector, a light electrode can be obtained. Moreover, since the active material is filled in the cell, there is no risk of the active material peeling or dropping even if the number of stacked cells is increased to increase the total amount of the active material. High capacity can be realized.
[0031]
Furthermore, according to the invention of claim 3, since the organic sheet material constituting the honeycomb-shaped formed body is soft and can be glued, it is easy to form a corrugated shape, overlap with a flat sheet, or form a spiral. Various commercially available cardboards can also be used in a spiral shape, and a desired current collector having a honeycomb structure can be easily obtained. Moreover, since the carbonaceous honeycomb structure obtained by calcination and carbonization of a honeycomb-shaped formed body made of an organic sheet material in a non-oxidizing atmosphere is lightweight, the electrode of the lithium ion secondary battery can also be lightened. .
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of an embodiment of a honeycomb structured current collector for an electrode of a lithium ion secondary battery according to the present invention.
FIG. 2 is a partially enlarged cross-sectional view of FIG.
3 is a schematic perspective view of an embodiment of an electrode for a lithium ion secondary battery using the current collector of FIG. 1. FIG.
4 is a partially enlarged sectional view of FIG. 3;
FIG. 5 is an explanatory view of an arrangement of an embodiment of an apparatus used for manufacturing a current collector according to the present invention.
FIG. 6 is a schematic diagram of an average microstructure of a carbonaceous honeycomb structure obtained in an example by SEM observation.
FIG. 7 is a charge / discharge characteristic curve.
FIG. 8 is a discharge amount curve.
FIG. 9 is a schematic view showing the structure of a conventional lithium ion secondary battery.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Current collector 11 Carbon honeycomb structure 12 Cell 13 Partition 15 Titanium nitride film 20 Electrode 21 Active material

Claims

An electrode of a lithium ion secondary battery, wherein a titanium nitride film is deposited on the partition wall surface of the cell including the outer surface of the carbonaceous honeycomb structure, and the cell diameter d of the carbonaceous honeycomb structure is 500 to 700 μm Honeycomb structure current collector.

An electrode for a lithium ion secondary battery, wherein the cells of the honeycomb structure current collector of claim 1 are filled with an active material for a positive electrode or a negative electrode, and the cell diameter d of the honeycomb structure is 500 to 700 µm .

When manufacturing a current collector for an electrode of a lithium ion secondary battery in which a positive electrode or negative electrode active material is filled in a honeycomb structure cell,
A honeycomb formed body formed from an organic sheet material carbonized by thermal decomposition is calcined and carbonized in a non-oxidizing atmosphere to form a carbon honeycomb structure having a cell diameter d of 500 to 700 μm .
The carbonaceous honeycomb structure is placed in a gas phase reactor, and a source gas for generating titanium nitride by a chemical reaction is repeatedly supplied and exhausted as a pulse of several thousand times or more at 750 to 1100 ° C. in the gas phase reactor. Thus, a titanium nitride film is deposited on the partition wall surface of the cell including the outer surface of the carbonaceous honeycomb structure, and the method for producing a honeycomb structure current collector for an electrode of a lithium ion secondary battery is provided.