March 2023
Intermediate
240 pages
7h 3m
Japanese
Content preview from 図解まるわかり 電池のしくみ
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138
スタンダードで最 強な
リチウムイオン電池
コバルト、エネルギー密度、有機溶媒
4-5
コバルトをめぐる不都合な現実
コバルト酸リチウムイオン電池（LCO）の正極活物質に使用されている
コバルトは高価なレアメタルです。そこで長年、他の安価な正極活物質を
用いた研究がされてきましたが、現在でもコバルトが主流です。その理由
には、まずコバルト酸リチウムが比較的容易に製造可能で、取り扱いが簡
単なことがあります。また後発のリチウムイオン電池と比べても、起電力
が3.7V と圧倒的に高く、性能がよいことが挙げられます。
しかし図4-9 のようにコバルトを採掘できる国が限られており、特に独
裁的な国での環境や人権問題が指摘されています。また埋蔵量も不明で、
資源の枯渇問題も浮上してきていますが、それでも使い続けているのが現
状です。
コバルトが最強な理由と使用上の注意点
リチウムイオン電池の利点は、そのままコバルト酸リチウムイオン電池
のものです。まずリチウムのイオン化傾向が大きい（図 1-14）ため他の
二次電池に比べて電圧が高く、大容量です（図 4-10）。リチウムを使え
ば、エネルギー密度も圧倒的に大きく、軽量の製品が作られます。自己放
電が小さく、サイクル寿命も長いため、何度も繰り返し充放電して使用で
きます。有害な重金属を使用していないので、環境に対する負荷が少ない
です。リチウム一次電池と同様に、電解質に有機溶媒を用いているため、
氷点以下の低温での使用も可能です（2-11）。
一方で過充放電すると、コバルト系の結晶は変形しやすい層状岩塩構造 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.