The criteria for evaluating lithium–air batteries in laboratory-based experiments are proposed for accurately predicting the performance of practical cells in industry.
Lithium‐oxygen batteries (LOBs) are promising next‐generation rechargeable battery candidates due to theoretical energy densities that exceed those of conventional lithium‐ion batteries. Although LOB with high cell level energy density has been demonstrated under lean electrolyte and high areal capacity conditions, their cycle life is still poor, and the cell degradation mechanism remains unclear. In the present study, by use of a three‐electrode electrochemical setup and in situ MS analytical techniques, it is revealed that the reaction efficiency of the negative lithium electrode largely decreases due to chemical crossover from the positive oxygen electrode side, such as H2O and CO2. Based on this mechanistic understanding, a LOB with an ultra‐lightweight flexible ceramic‐based solid‐state separator with 6 µm thickness that effectively protects the lithium electrode against chemical crossover without diminishing the energy density of LOBs is fabricated. Notably, a 400 Wh kg−1 class LOB exhibits a stable discharge/charged process for >20 cycles. The strategy demonstrated in this study sheds light on the direction for the practical implementation of LOBs with high energy densities and long cycle lives.
Porous architecture is key in the nonaqueous lithium−oxygen (Li−O 2 ) electrode process, which is attracting huge interest because of its application in reversible energy storage with high theoretical energy density. However, it is still challenging to understand the optimal porous structure to obtain high reversibility of the reaction. One main reason is because of instability and undefined porous structures of standard electrodes consisting of carbonaceous materials, and this issue hinders from unveiling the fundamental mechanism in the complicated electrode process. Here, we developed a new synthetic strategy to design monolithic electrodes of pure metallic nickel with controlled bimodal porous structures. The present work aims to investigate the fundamental effects of the bimodal macroporous structure in the Li−O 2 electrode process under carbon-/binder-free stable model electrodes. As the result, we found that, depending on the multiscale structural configurations, the bimodal macroporous structure gave significant influences to key properties, such as the efficiency of redox-mediators, discharge overpotential, and cycling life. This work indicates that the rational design of stable and conductive porous materials is one of the promising approaches to investigate highly complicated electrochemical reactions in porous electrodes and suggest new guidelines for further development of hierarchically structured electrodes toward advanced electrochemical systems.
The realization of secondary lithium–oxygen
batteries (Li–O2 batteries, LOBs) with large gravimetric
energy density requires
the development of an innovative electrolyte with high chemical stability
that allows the charge–discharge reaction to proceed with low
overvoltage. In this study, we evaluated the potential of an electrolyte
solvent, N,N-dimethylethanesulfonamide
(DMESA) with a sulfonamide functional group, at a current density
of 0.4 mA cm–2 and a capacity of 4 mA h cm–2. The voltage at which CO2 was generated during charging
was substantially higher than that of a tetraglyme (G4)-based electrolyte
with redox mediators, which is one of the standard electrolytes used
for LOBs. Experiments using a 13C-containing positive electrode
revealed that CO2 generated during charging mainly originated
from the decomposition of the positive electrode. The analyses of
the charging profile in conjunction with differential electrochemical
mass spectrometry suggested the formation of highly degradable lithium
peroxide (Li2O2) in the DMESA-based electrolyte.
The formation of highly degradable Li2O2 enables
a reduction of the charging voltage, leading to further suppression
of the electrolyte decomposition.
Self-standing porous carbon electrodes mainly composed of mesopores with a three-dimensional hexagonal array exhibited superior lithium–oxygen battery performance under low electrolyte/areal capacity (E/C < 10 g A−1 h−1) conditions.
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