J. Electrochem. Sci. Technol., 2020, 11(4), 430-436 - 430 - Electrochemical Properties of Acetylene Black/Multi-walled Carbon Nanotube Cathodes for Lithium Thionyl Chloride Batteries at High Discharge Currents Hee-Youb Song 1 , Moon-Hyung Jung 2 , and Soon-Ki Jeong 3, * VIZTRO MILTECH., Cheonan, Chungnam, 31214, Korea VITZROCELL Co., Ltd., 70, Indeoseupakeu, Hapdeok, Dangjin, Chungnam 31816, Korea Department of Energy Systems, Soonchunhyang University, Asan, Chungnam, 31538, Korea ABSTRACT Lithium thionyl chloride (Li/SOCl ) batteries exhibit the highest energy densities seen in commercially available primary batteries because of their high operating voltages and discharge capacities. They are widely used in various extreme envi- ronments; however, they show signs of degradation at high discharge currents. The discharge performance of Li/SOCl is considered to be greatly dependent on the carbon materials used in the cathode. Therefore, suitable carbon materials must be chosen to improve discharge performances. In this work, we investigated the discharge properties of Li/SOCl batteries in which the cathodes contained various ratios of acetylene black (AB) and multi-walled carbon nanotubes (MWCNTs) at high discharge currents. It was confirmed that the MWCNTs were effectively dispersed in the mixed AB/MWCNT cath- odes. Moreover, the discharge capacity and operating voltage improved at high discharge currents in these mixed cathodes when compared with pure AB cathodes. It was found that the mesopores present in the cathodes have a strong impact on the discharge capacity, while the macropores present on the cathode surface influence the discharge properties at high dis- charge rates in Li/SOCl batteries. These results indicate that the ratio of mesopores and macropores in the cathode is key to improving the discharge performance of Li/SOCl batteries, as is the dispersion of the MWCNTs. Keywords : Lithium Thionyl Chloride, Multi-Wall Carbon Nanotube, Acetylene Black, Lithium Primary Batteries Received : 9 July 2020, Accepted : 13 August 2020 1. Introduction Lithium thionyl chloride (Li/SOCl 2 ) primary bat- teries have been widely used as power sources in extreme environments because of their high operat- ing voltage (3.6 V), wide operating temperature range (-55–85 o C), and high discharge capacity (0.8 Ah, AA size, wound type) [1-4]. In general, Li/SOCl 2 batteries consist of a lithium metal anode, a carbon- based cathode, and SOCl 2 containing a lithium salt as the electrolyte solution. During the discharge pro- cess, the lithium metal is oxidized and the SOCl 2 electrolyte solution is reduced to produce sulfur, sul- fur dioxide, and lithium chloride. The carbon cathode acts as a catalytic surface for the reduction of the SOCl 2 [1-3], and the surface structure of the carbon cathode is of particular importance due to the forma- tion of insoluble reaction products such as lithium chloride on the carbon surface [5-11]. Lithium chlo- ride exhibits a low electrical conductivity, thereby hindering the reduction of SOCl 2 , and so the presence of lithium chloride in the pores of the carbon cathode can make the diffusion of SOCl 2 during the discharge process more difficult. These issues must therefore be addressed to allow for the broader application of Li/ SOCl 2 batteries. The discharge performances of Li/SOCl 2 batteries are greatly dependent on the physicochemical proper- ties of the carbon cathode materials employed. For example, carbon nanotubes (CNTs) could improve the discharge performance at high discharge currents due to their high electrical conductivity and high spe- cific surface area. As such, the catalytic effects of Research Article *E-mail address: [email protected]DOI: https://doi.org/10.33961/jecst.2020.01179 This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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J. Electrochem. Sci. Technol., 2020, 11(4), 430-436
− 430 −
Electrochemical Properties of Acetylene Black/Multi-walled Carbon
Nanotube Cathodes for Lithium Thionyl Chloride Batteries at
High Discharge Currents
Hee-Youb Song1, Moon-Hyung Jung2, and Soon-Ki Jeong3,*1VIZTRO MILTECH., Cheonan, Chungnam, 31214, Korea2VITZROCELL Co., Ltd., 70, Indeoseupakeu, Hapdeok, Dangjin, Chungnam 31816, Korea3Department of Energy Systems, Soonchunhyang University, Asan, Chungnam, 31538, Korea
ABSTRACT
Lithium thionyl chloride (Li/SOCl2) batteries exhibit the highest energy densities seen in commercially available primary
batteries because of their high operating voltages and discharge capacities. They are widely used in various extreme envi-
ronments; however, they show signs of degradation at high discharge currents. The discharge performance of Li/SOCl2 is
considered to be greatly dependent on the carbon materials used in the cathode. Therefore, suitable carbon materials must
be chosen to improve discharge performances. In this work, we investigated the discharge properties of Li/SOCl2 batteries
in which the cathodes contained various ratios of acetylene black (AB) and multi-walled carbon nanotubes (MWCNTs) at
high discharge currents. It was confirmed that the MWCNTs were effectively dispersed in the mixed AB/MWCNT cath-
odes. Moreover, the discharge capacity and operating voltage improved at high discharge currents in these mixed cathodes
when compared with pure AB cathodes. It was found that the mesopores present in the cathodes have a strong impact on
the discharge capacity, while the macropores present on the cathode surface influence the discharge properties at high dis-
charge rates in Li/SOCl2 batteries. These results indicate that the ratio of mesopores and macropores in the cathode is key
to improving the discharge performance of Li/SOCl2 batteries, as is the dispersion of the MWCNTs.
This is an open-access article distributed under the terms of the Creative CommonsAttribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0)which permits unrestricted non-commercial use, distribution, and reproduction in anymedium, provided the original work is properly cited.
Hee-Youb Song et al. / J. Electrochem. Sci. Technol., 2020, 11(4), 430-436 431
CNTs in Li/SOCl2 batteries have been widely investi-
gated [12-19]. However, the impact of their structure
on the discharge performance of Li/SOCl2 batteries is
not yet clearly understood. Additionally, their nano-
structures allow the facile formation of aggregates,
which may cause a deterioration in the battery perfor-
mance. Therefore, technologies aimed at the disper-
sion of CNTs in the cathodes are key to improving
the discharge performances of Li/SOCl2 batteries.
Commercially, mixtures of acetylene black (AB) and
ketjen black have been widely used as a cathode
material in Li/SOCl2 batteries. However, the dis-
charge performances of such systems at high dis-
charge rates are generally poor under extreme
environments. To address this issue, we wished to
consider a new composite electrode, namely AB/
multi-walled carbon nanotube (MWCNT), as the bat-
tery cathode material, with the aims of improving the
discharge performance at high discharge rates. Thus,
we herein report our investigation into the effect of
AB addition on the effective dispersion of MWCNTs
in cathodes, and the impact of mixing AB and
MWCNTs on the discharge performance of Li/SOCl2
batteries by investigating the discharge properties of
AB/MWCNT mixed cathodes at discharge currents
of 150 and 600 mA. In addition, the correlation
between the discharge properties and the physical
properties of AB/MWCNT mixed cathodes are dis-
cussed.
2. Experimental
2.1 Preparation of cathode materials
Cathode materials were prepared using AB (Denka
black, Denka Co. Ltd., Tokyo, Japan) and MWCNTs
(LUCAN BT1003M, LG Chem. Seoul, Korea) with
AB:MWCNT weight ratios of 0:10, 3:7, 5:5, 7:3, and