Resistance Reduction Effect by SDX ® in Lithium-Ion Batteries

1. Introduction Practical uses of lithium-ion batteries(LIB) are rapidly growing especially in large batteries for full electric vehicle(EV), plug-in hybrid electric vehicle(PHEV) and so on, but improvements of their characteristics(“high-energy density”, “high power”, “long cycle-life”, “safety” and “lower cost”) are still strongly demanded. SDX ® is a surface coated aluminum current collector(AL) with carbon black(CB) and organic binder, and the thickness of the coated layer is about 1μm, and SDX ® makes a cell internal resistance lower and adhesion between cathode active materials and AL stronger, so as to improve battery performance dramatically[1,2]. The control of the internal resistance of LIB by the clarification of the mechanism is one of the biggest key items to improve them. So the mechanisms of the interface resistance between cathode active material layer and AL have been investigated and discussed[3]. In general, cell internal resistance is separated simply into electronic resistance and ionic resistance. We successfully separated the electronic resistance into material resistance and interface resistance between cathode active material layer and AL. And then we independently measured the material resistance and the interface resistance by Electrode Resistance Meter(HIOKI E.E. CORPORATION) which can separate electrode resistance into material and interface resistance. In the battery which used LFP as cathode active material, the quantitative investigation of the contribution of SDX ® and conducting additives to the electronic resistance reduction was provided by the result of measurement using Electrode Resistance Meter(Fig.1). The interface resistance of the cathode with AL was higher than the material resistance of that by almost one order of magnitude. The interface resistance of the cathode with SDX ® was lower than that with AL by almost one order of magnitude. It is not only presumed that the interface resistance is dominant in the electronic resistance but confirmed that the interface resistance is maintained at lower level by SDX ® . Because the interface resistance was reduced by SDX ® , it has been reported that conducting additives could be reduced much in cathode[4]. By application of SDX ® , it was confirmed that the interface resistance of LFP could be decreased largely irrespective of a distribution state of conducting additives. As a result, cell internal resistance and discharge capacity retention of LFP was constant irrespec