Effect of Conductive Agent on Electrochemical Properties of Next Generation Lib

Introduction

In general, the carbon black (CB) such as furnace black (FB) and acetylene black (AB) have been used as conductive agent for lithium ion battery (LiB). Recently, the powder properties of them seem to be very similar. Very recently towards next-generation high energy density LiB, various approaches has been reported.^1,2In such high energy density application, the amount of conductive agent tends to be reduced as much as possible. However, by the present, there have been very few reports on conductive agent, in older to possess sufficient conductivity even in less amount of conductive agent. In this study, the influence of the carbon black as conductive agent on electrical performance has been investigated. Moreover, the mechanism was considered from the view of morphology inside electrodes.   

Experimental

Conductive agents were prepared various CBs that were synthesized by different production method and morphology such as AB and FB. For fabricate cathode electrode, LiNi_0.5Mn_0.3Co_0.2O₂as cathode active material, CB and PVdF have been made kneading with a mass ratio of 95: 3: 2. The obtained electrode has been set in a simple SUS two-pole cell, and then electronic resistance was measured by impressing direct current electricity. The fundamental electrochemical performances were evaluated by using system Li metal | 1M LiPF6/ECand DEC(3:7 vol%) | positive electrode(2032 type coin cell). For investigating the morphology of positive electrode, SEM (JSM-7000,JEOL) performed observation of the electrode surface and cross section.

Result and Discussion 

Table 1 shows powder properties of conductive agent. Fig. 1 shows the powder characteristics of CB have influenced on the rate properties. AB1 had superior rate properties as compared to the other CBs. Fig. 2 shows the SEM images of the electrode cross section using AB1 and AB2. The electrodes fabricated with AB1 had homogeneous microstructure, while the electrodes fabricated with AB2 had heterogeneous because of agglomeration of AB and PVdF(Black contrast area). These results imply that the electrode with more homogeneous microstructure had superior rate property.  In particular, since the amount of conductive agents should be decreased to achieve higher energy density of LiB, the dispersibility(= homogeneous microstructure electrode) of CB and PVdF might be more important than those in previous LiB. To decrease agglomeration of CB and PVdF, it is needed to choose optimized CB. In this study, all the electrodes have been fabricated by same PVdF, so that the dispersibility of electrodes might be mainly affected by the CB powder characteristics. The other CBs that have various morphology have been analyzed. Further result and discussion in detail will be presented on the day of meeting.

Reference

1. T. Ohzuku at al., J. Mater. Chem., 21, 10179 (2011).
2. A. R. Armstrong, et al,. J. Am. Soc., 128, 8694 (2006).