成果報告書詳細
管理番号20110000000661
タイトル*平成22年度中間年報 次世代自動車用高性能蓄電システム技術開発 次世代技術開発 構造規制型新規金属負極の研究開発
公開日2012/6/27
報告書年度2010 - 2010
委託先名公立大学法人首都大学東京
プロジェクト番号P07001
部署名スマートコミュニティ部
和文要約1. 研究開発の内容及び成果等
本研究提案の内容は構造を規制した電極を作製することにより、リチウム金属負極および合金系負極のサイクル安定性を向上させ、本来これらの負極材料が有している高いエネルギー密度をリチウム二次電池に応用可能にする点にある。本年度は、リチウム金属負極および合金系負極に関して下記項目について重点的に研究を行った。
(1) 3DOM構造を応用したリチウム金属負極の特性向上
平成21年度に、三次元規則配列構造を有するポリイミド多孔膜(3DOMポリイミド膜)をリチウム金属二次電池用セパレータに適用し、リチウムデンドライトの析出を効果的に抑制できること見出した。また、3DOMポリイミド膜の細孔径が1 μmから250 nmへ小さくなるにつれて、リチウム金属の溶解析出反応が安定化されることを見出した。この結果に基づき、本年度は細孔径が250 nmの3DOMポリイミド膜をリチウム金属二次電池のセパレータに適用し、特に電解液の種類がリチウム金属負極の特性に及ぼす影響に着目し研究を推進した。また、リチウム金属を二次電池の負極として実用することを目的とし、フルセル試験を実施した。
英文要約Title: Development of High-performance Battery System for Next-generation Vehicles / Next-generation Technology Development / Development of Three-dimensionally Ordered Electrodes for Lithium Metal and Alloy Anodes (FY2007-FY2012) FY2010 Annual Report

In order to realize high energy density batteries, new anode and cathode materials should be developed with practical cycle life. Both lithium metal and alloy anodes have higher energy density than that of graphite electrode. However, both electrodes have serious problem which is a very low cycleability. In this project, we proposed the technology of three-dimensionally ordered electrodes for lithium metal and alloy anode. In this year, we have focused on (1) three-dimensionally ordered macroporous (3DOM) separators for lithium metal anode and (2) a micro-domain structure for Sn-Ni alloy anode.

(1) 3DOM separators for lithium metal anode
The cycleability of lithium metal anode is strongly limited by a formation of lithium dendrite. Therefore, lithium dendrite formation has to be suppressed for the practical application of lithium metal anode. We have revealed in FY2009 that a three-dimensionally ordered macroporous (3DOM) structure of polyimide, i.e., 3DOM polyimide separator, effectively suppressed the growth of lithium dendrite and provided good cycleability over 1000 cycles to lithium metal anode. In FY2010, the effect of electrolyte solution on the cycleability of lithium metal anode was precisely evaluated by using a symmetrical cell with lithium metal / 3DOM polyimide separator (pore size: 250 nm, thickness: 30 µm, various carbonate containing 1 mol dm-3 LiPF6) / lithium metal configuration. It was clearly observed in the galvanostatic charge/discharge test under DOD = 25% condition against lithium metal electrode that the cycleability of cell was strongly affected by the kind of carbonate. Particularly, 1 mol dm-3 LiPF6 + ethylene carbonate (EC) provided excellent cycleability over 3000 cycles to the symmetrical cell. Based on this result, we also fabricated and tested a full cell composed of lithium metal anode (9.65 mA h) and lithium nickel-cobalt-aluminum oxide (NCA) cathode (2.0 mA h). The full cell was successfully charged and discharged over 300 cycles without a remarkable capacity fading, under the condition of full use of NCA cathode (charge: 0.1 C, discharge: 1 C). The SEM observation after the cycle test revealed that the morphology of lithium metal anode in the full cell was relatively smooth and any lithium dendrite was not confirmed.

(2) micro-domain structure for Sn-Ni alloy anode
The problem of Sn-Ni alloy is a poor cycleability due to the large volume change of during charge and discharge processes. In FY2009, we introduced a micro-domain structure into 3DOM Sn-Ni alloy electrode for inhibition of fragmentation due to the large volume change of during charge and discharge processes. Micro-domain structure was prepared by using a photoresist pattern with ordered cylindrical pores (diameter: 20 m, depth: 30 m). 3DOM Sn-Ni alloy with cylindrical domain structure maintained 100% of capacity after 200 cycles under the condition of DOD = 77 % (500 mA h g-1). However, the substrate (current collector) used for fabricating 3DOM Sn-Ni alloy with cylindrical domain structure was a hard silica/silicon substrate, which strongly limited the application of structured Sn-Ni alloy anode. In FY 2010, we formed the cylindrical domain structure of Sn-Ni alloy on a flexible copper current collector, and successfully enlarged the size of electrode sheet. Furthermore, application of the structured Sn-Ni alloy as power for preparing conventional composite electrodes was also considered. In the composite electrode, the cycleability of structured Sn-Ni alloy is expected to be greatly increased by appropriate combination with electrode additives such as binders and conductive materials. The full cell test is now underway in a laminate-type cell.
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