SDX ® which is surface coated aluminum current collector (AL) with carbon black and organic binder, makes a cell resistance lower and adhesion between cathode active material and AL stronger, so as to improve battery performances dramatically. The cell resistance was separated simply into electronic resistance and ionic resistance. We successfully separated the electronic resistance into material resistance and interface resistance between cathode active material 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 this paper, more detailed examinations were carried out, and the mechanism of decreasing resistance by SDX ® in lithium ion battery (LIB) was tried to be clarified.

SDX ® which is surface coated aluminum current collector (Al) with carbon black and organic binder, makes a cell resistance lower and adhesion between cathode active material and Al stronger, so as to improve battery performances dramatically. The cell resistance was separated simply into electronic resistance and ionic resistance. We successfully separated the electronic resistance into material resistance and interface resistance between cathode active material 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 this paper, more detailed examinations were carried out, and resistance reduction effect by SDX ® in lithium ion battery (LIB) was tried to be clarified.

We have developed SDX TM , aluminum foil with a conductive carbon layer, to reduce cell resistance. SDX TM also showed high rate performances. To reveal that mechanism, we prepared aluminum foil with various chemical forming layers for studying of resistance and compared to two famous theories about conductive mechanism of carbon particles and aluminum foil.

1. Introduction  Practical uses of lithium-ion batteries are rapidly growing especially in large batteries for electric vehicles (EV), energy storage systems (ESS) and so on, but improvements of their characteristics still are strongly demanded.  Large improvements of battery characteristics of LFP (LiFePO4) and NMC (LiNi1/3 Mn1/3 Co1/3 O2) as cathode active material, by using ‘SDXTM’ which is a conducting carbon coated aluminum current collector, have been reported [1,2].  The control of internal resistance of lithium ion batteries by the clarification of mechanism of internal resistance is one of the biggest key items to improve them. So the mechanisms of interface resistance between aluminum current collector and cathode active material layer have been investigated and discussed [3].  In the battery which used LFP as cathode active material, recently the quantitative investigation of contribution to electronic resistance reduction of SDXTMand conducting additives was provided by the result of measurement using ELECTRODE RESISTANCE METER (Under development by HIOKI E.E. CORPORATION) which could divide electrode resistance into material resistance and interface resistance (Fig.1). The interface resistance of the cathde with aluminum current collectors was higher than the material resistance of that by almost one order of magnitude. The interface resistance of the cathode with SDXTMwas lower than that with aluminum current collectors by almost one order of magnitude. Because the interface resistance was reduced by SDXTM, it was reported that conducting additives were able to be reduced much in cathode [4]. In this paper, more detailed examination will be carried out, and the effect of SDXTMin lithium ion battery will be tried to be clarified. 2. Experiment  The preparation of electrode slurry was carried out by dispersing LFP as cathode active material, conducting additives and polyvinylidene difluoride (PVdF) into N-methylpyrrolidone (NMP). Cathode electrodes were prepared by coating the slurry onto SDXTM or aluminum current collectors in several coating speeds (e.g. 300, 400 or 500mm/min), by drying and by pressing them. Artificial graphite (SCMGTM) was used for anode active material, and similarly anode electrodes were prepared by coating its slurry (aqueous solution) onto copper current collectors, by drying and by pressing them. By laminating one sheet of anode and one sheet of cathode, pouch type cell was assembled. 3. Results and discussion  The material resistance and the interface resistance of the cathode were measured by ELECTRODE RESISTANCE METER (Fig.2). In each coating speed, the interface resistance of the cathode with aluminum current collectors was higher than the material resistance of that. The interface resistance of the cathode with SDXTM was lower than that with aluminum current collectors, and it was almost same as the material resistance of the cathode with SDXTM. The interface resistance of the cathode with aluminum current collectors increased when the coating speed increased, but the interface resistance of the cathode with SDXTMwas constant without depending on coating speed. Cell DCRs were measured (Fig.3). The cell DCR with aluminum current collectors increased when the coating speed increased, but the cell DCR with SDXTMwas constant without depending on coating speed. It was confirmed that the cell DCR with aluminum current collector showed similar behavior to the interface resistance of the cathode with aluminum current collector. The visualization results of a dispersion state of conducting additive in an electrode will be presented. References 1. M. Ohmori et al., Electrochemistry, 78, 308, (2011) 2. M. Ohmori et al., Electrochemistry, 79, 165, (2012) 3. M. Ohmori et al., Prime2012 4. A. Takeda, H. Yokouchi, H. Tomozawa, Electrochemistry, 2C25, (2015) Figure 1