Energy
Electric vehicle, Energy storage, Smart device

Design of new liquid electrolyte materials
for next-generation rechargeable batteries
Department of Energy and Environmental Materials, SANKEN (The Institute of Scientific and Industrial Research)
Professor Yuki Yamada
https://researchmap.jp/yuki_yamada?lang=en

Abstract
Lithium metal is an ideal negative electrode for rechargeablebatteries. It has been studied for various next-generation battery
concepts such as lithium metal batteries, lithium sulfur batteries,and lithium oxygen batteries. However, the high reactivity (strongreducing power) of lithium metal causes electrolyte decomposition,resulting in low charge-discharge efficiency. We demonstrated a
new method to control the reactivity of lithium metal by electrolyte
design. Based on this concept, we proposed several electrolytematerials that can weaken the reactivity of lithium metal and lead tohigh charge-discharge efficiency of over 99%.

Energy▍ Background & Results
Lithium-ion batteries are indispensable devices in our daily lives
because they are widely used in smartphones, notebook PCs,
household storage batteries, and electric vehicles (EVs). However, the energy density (stored energy per unit weight or volume)of lithium-ion batteries is reaching a theoretical limit, and various
next-generation battery concepts are being studied to achievemuch higher energy density. Lithium metal negative electrodes
have been a central subject of research and development because
the theoretical capacity of lithium metal (plating/stripping reaction:
Li+ + e- ⇌ Li) is 3,860 mAh/g, which is about 10 times higher thanthat of graphite (372 mAh/g) used in commercial lithium-ion batteries. The major issue of lithium metal that hampers its practicalapplication is low charge-discharge efficiency due to electrolyte
decomposition caused by the high reactivity (strong reducingpower) of lithium metal. It has been shown that charge-discharge
efficiency strongly depends on the electrolyte formulations, but itis thought to be due to the difference in passivation films formedon the surface of lithium metal by electrolyte decomposition. There
has been no quantitative discussion on how charge-discharge efficiency is dominated by electrolyte formulations.
In this study, we found that the reaction potential (reactivity orreducing power) of lithium metal differs significantly dependingon the electrolyte formulations and that the charge-discharge
efficiency is closely correlated with the reaction potentials. The
charge-discharge efficiency of lithium metal tends to increase
when its reaction potential is high (low reactivity or low reducingpower) in a specific electrolyte formulation. In addition, we investigated the relationship between the reaction potentials of lithium
metal and the liquid structures of electrolyte solutions. We foundthat the ion-paring state of lithium ion and counter anion dominates
the reaction potential. By designing the electrolyte with extensive
ion pairing, the reaction potential of lithium metal can be increased,
which in turn increases the charge-discharge efficiency. Based on
the proposed mechanism, we proposed several electrolyte materials that achieved high charge-discharge efficiencies of over 99%.

▍ Significance of the research and Future perspective
This finding provides a clear guideline for the electrolyte designof next-generation batteries that employ lithium metal negativeelectrodes and will greatly accelerate research and development
toward their practical application. Replacing commercial graphite
negative electrodes for lithium metal will increase the theoreticalenergy density of lithium-ion batteries by approximately 1.4 times.
Furthermore, the energy density may be increased by several
times when lithium metal negative electrodes are paired with
next-generation high-capacity positive electrodes such as sulfur
or oxygen. Such next-generation rechargeable batteries with highenergy density are promising for use in EVs. They can achieve acruising range comparable to those of gasoline cars.

Fig.1

Fig.2

P a t e n t Japanese Patent Application No. 2021-164244
Ko, Seogjae; Yamada, Atsuo; Yamada, Yuki et al. Electrode potential influences the reversibility of lithium-metal anodes, Nat. Energy, 2022, 7, 1217,
T r e a t i s e doi: 10.1038/s41560-022-01144-0
Yamada, Yuki et al. Advances and issues in developing salt-concentrated battery electrolytes, Nat. Energy, 2019, 4, 269, doi: 10.1038/s41560-019-0336-z
UR
L https://www.sanken.osaka-u.ac.jp/labs/eem/en/
K e y w o r d rechargeable battery, lithium metal, electrolyte, high energy density