Thickness Dependence of Resistance Components of a LiNi x Co y Mn 1-x-y O 2 -Based Positive Electrode for Lithium Ion Batteries

Abstract

Dependence of charge-transfer resistance ( R ct ) on thickness of positive electrodes for high-power lithium-ion batteries (LIBs) was investigated. The results of the investigation show that R ct of a LiNi x Co y Mn 1-x-y O 2 (NCM)-based positive electrode is increased by decreasing electrode thickness to less than 15 μ m, while R ct of electrodes with thickness greater than 15 μ m stayed almost constant. Scanning spreading resistance microscopy indicated that the electronic resistances of thinner electrodes were higher than those of thicker electrodes. Given that result, we consider that the formation of an electrically conductive network in the thinner electrode is insufficient compared to that formed in the thicker electrode. Focused-ion-beam scanning-electron-microscopy observation of an electrode with a higher R ct revealed that acetylene black (AB) as an electron conductor and poly-vinylidene-difluoride binder were agglomerated non-uniformly, and large pores formed among the non-uniform aggregates. Presumably, the non-uniform distribution of aggregates and formation of large pores resulted in an insufficient electrically conductive network between the aggregates, which resulted in increased R ct .