報告書番号

T52

タイトル（和文）

電力貯蔵用大型リチウム二次電池の正極・負極材料の開発に関する研究

タイトル（英文）

Studies on Positive and Negative Electrode Materials of Lithium Secondary Batteries for Electric Power Storage.

概要 （図表や脚注は「報告書全文」に掲載しております）

常温作動、無保守で高エネルギー密度・高効率を有するリチウム二次電池の電力貯蔵用途への実用化が期待されており、高容量化、高出力化、サイクル寿命の向上を目指して材料ベースでの研究開発が進められている。 正極材料として、アニオンのドープ・脱ドープが充放電反応を決定する電子伝導性高分子の中からポリアニリンを取り上げ、電力貯蔵用としての大型化・実用化に向けた評価を行うために、以下の諸点に着目して研究開発を行った。電解重合法によるアニリンモノマーからの合成と重合条件および重合後の洗浄処理が正極特性に及ぼす影響を明らかにした。これにより、電解重合反応の明確化と初期アニオンドープ率を含む重合ポリアニリンの構造式の明らかにした。また、重合ポリアニリン膜の微細構造を明らかにし、ポリアニリン固相内でのアニオン移動について速度論的な解析を行った。 負極炭素材料としてカーボンブラックを取り上げ、負極性能を決定する材料サイドからの因子を種々の観点から検討し、以下の点を明らかにした。カーボンブラック合成後の熱処理に伴う結晶性の変化および合成条件を変えた場合のマクロ構造の変化が負極特性に及ぼす影響を明らかにした。また初期還元時の電極挙動について、電解液との相互作用による不可逆反応について検討し、反応機構の明確化とその後の不可逆反応抑制機能の解明を行った。 以上の研究開発は、リチウム二次電池の電力貯蔵用として大型化に向けて材料設計、開発指針を与える新しい方向付けを行うことができ、実用化が近づいたものと期待される。

概要 （英文）

Large-scale lithium secondary batteries having both high energy density and high energy efficiency are well-suited for electric vehicles and electric power load-leveling systems. Therefore, various studies on their component materials have been conducted to improve battery performance in areas such as cycleability and rate capability. In this study, both polyaniline (PAn) as a positive electrode material and carbon black (CB) as a negative electrode material were investigated to enhance the possibility for a practical use.As for PAn, the following facts have been revealed experimentally: (1) PAn films prepared in 2 M HClO4 solutions galvanostatically contained one ClO4－ ion per two aniline units as a dopant, which can be removed partially by rinsing with water or a neutral solution free from a perchlorate salt. In charge-discharge cycling tests, a PAn film having the initial doping level of ca. 50 % exhibited reversible changes stably corresponding to the anion amount of ca. 55 % per aniline unit. (2) The diameter of PAn fibrils decreased from 2.2 to 0.4 μm with increasing the polymerization current density. The discharge capacity of a PAn film in a PC solution decreased with increasing the polymerization current density.(3) Diffusion coefficient of ClO4－ ion in PAn fibrils having various radii was determined by three different electrochemical measurements: current pulse, potential step and AC impedance methods. It was about 10-13 cm2/s, typically independent of fibril radius and tended to decrease with the discharged extent. The thinner fibrils having a shorter diffusion length and a large effective surface area are expected to give better electrode performance.As for CB, on the other hand, the following facts have been revealed experimentally:(1) There were two electrochemically reversible processes. The first one at about 0.2 V, observed for all CB samples, was attributed to intercalation/de-intercalation of Li into/from CB matrix. Another one at about 0.9 V, which might be attributed to a redox process through a kind of passive surface film, was characteristic for CB samples treated at a low temperature.(2) About 90 % of the CB surface was covered with a smooth film about 1 - 1.5 nm in thickness after five cyclic voltammetry cycles. The X-ray photoelectron spectroscopy analysis revealed that this film contained oxygen atom bonding directly to the carbon atoms and was formed by decomposition of the solvent. The surface film was confirmed to be formed also by chemical reduction using lithium naphthalide, where lithium insertion in the CB took place. (3) The reversible capacity was independent on the BET area and was large for a highly aggregated coarse CB samples. The neck portion connecting two primary CB particles was considered as active for the insertion/extraction of lithium.In summary, many important knowledges could be deduced from this fundamental study to develop large-scaled lithium secondary batteries.

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