MODIFICATION OF LiCI-LiBr-KBr
ELECTROLYTE FOR LiAl/FeS2 BATTERIES
T. D. Kaun, A. N. Jansen,
G. L. Henriksen, and D. R. Vissers
Argonne National Laboratory
Chemical Technology Division
9700 South Cass Avenue
Argonne, IL 60439
ABSTRACT
The bipolar LiAI/FeS2 battery is being developed to achieve the high
performance and long cycle life needed for electric vehicle application. The
molten-salt (400 to 440*C operation) electrolyte composition for this battery has
evolved to support these objectives. An earlier change to LiCI-LiBr-KBr
electrolyte is responsible for significantly increased cycle life (up to
1000 cycles). Recent electrolyte modification has significantly improved cell
performance; approximately 50% increased power, with increased high rate
capacity utilization. Results-are based on power-demanding EV driving profile
test at 600 W/kg. The effects of adding small amounts (1-5 mol%) of LiF and
LiI to LiCl-LiBr-KBr electrolyte are discussed. By cyclic voltammetry, the
modified electrolytes exhibit improved FeS2 electrochemistry. Electrolyte
conductivity is little changed, but high current density (200 mA/cm2)
performance improved by approximately 50%. A specific feature of the LiI
addition is an enhanced cell overcharge tolerance rate from 2.5 to 5 mA/cm2.
The rate of overcharge tolerance is related to electrolyte properties and negative
electrode lithium activity. As a result, the charge balancing of a bipolar battery
configuration with molten-salt electrolyte is improved to accept greater cell-to-
cell deviations.
INTRODUCTION
The LiAl/FeS, bipolar battery is being developed to achieve the high performance and
long cycle life needed for electric vehicle batteries. The electrolyte used in this molten-salt
battery has a major impact on cell performance and cycle life. The initial development of the
LiAI/FeS2 cell, with LiCl-LiBr-KBr electrolyte (25-37-38 mol%), enhanced cycle life
dramatically (from 100 to about 1000 cycles) without severely compromising performance.
The lower temperature cell operation (400-425*C) increased cycle life [1]. The phase
diagram of the LiCI-LiBr-KBr (Fig. 1) has a broad liquidus range of composition related to
ion content. Its liquidus range of 1.25 to 2.6 Li+/K+ ratio at 400'C is of particular interest
to the dynamic conditions of electrode operation at high current density. Melting point and

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