Graphite-based
dual-ion batteries are a promising alternative to
the lithium-ion batteries for energy storage because of its potentially
lower cost, higher voltage, and better safety. Among the most important
materials in the dual-ion battery are the graphite and graphite intercalation
compounds (GICs), whose properties determine the performance of electrodes.
The GICs are formed at both anode and the cathode sides during the
charging process in which the graphene sheets and the intercalants
are arranged in an ordered way called the staging of GICs. Staging
is one of the important structural features of GICs related to the
volume expansion of the electrodes, the charging rate, and the capacity
of the battery. However, the details of the staging mechanism, such
as the structural properties, the electronic structure, and the voltage
dependence on the stages are still poorly understood. In this regard,
we perform density functional theory studies to explore these issues
in GICs. Using staging models, we examine the stability of GICs at
different stages of intercalation with a range of species (i.e., Li,
Na, K, PF
6
, BF
4
, TFSI, AlCl
4
, and
ClO
4
). We then study the contribution of intercalants to
the electronic band structures in GICs. In addition, the voltage profiles
of the dual-ion batteries with different intercalation species, intercalation
stages, and battery capacities are also analyzed. The present work
is important for the better understanding of graphite-based dual-ion
batteries and helpful in development of novel energy storage systems.
The dual‐ion battery (DIB) is a promising energy storage system that demonstrates high‐power characteristics and fast‐charging capability. However, conventional electrolytes are not compatible with the high‐voltage graphite cathode and the reactive Li metal anode, thus leading to the poor cycle stability and low Coulombic efficiency of the DIB. Here, an all‐fluorinated electrolyte is reported that can enable a highly stable operation of the graphite||Li DIB up to 5.2 V by forming robust and less‐resistive passivation films on both electrodes to reduce side reactions. The electrolyte allows reversible PF6– anion insertion/extraction and Li+ cation plating/stripping in the graphite||Li battery, achieving stable cycling with 94.5% capacity retention over 5000 cycles at 500 mA g–1, high capacity utilization of 91.8% of the available charge capacity at 50 C (5000 mA g–1), and also minimal self‐discharge. At a low temperature of 0 °C, this all‐fluorinated electrolyte exhibits 97.8% of the room temperature reversible capacity, along with ≈100% capacity retention after more than 3000 cycles, at 5 C. This work sheds a new light on the development of fluorinated electrolytes for high voltage and long‐lasting DIBs.
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