The
sodium ion battery (NIB) is a promising alternative technology
for energy storage systems because of the abundance and low cost of
sodium in the Earth’s crust. However, the limited cycle life
and safety concerns of NIBs hinder their large-scale applications.
Here, we report a nonflammable localized high concentration electrolyte
(sodium bis(fluorosulfonyl)imide-triethyl phosphate/1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl
ether (1:1.5:2 in molar ratio)) for highly reversible NIBs. By using
a cryo-transmission electron microscope, it was found that an ultrathin
(3 nm) and robust interphase layer formed on the cathode surface can
block transition metal dissolutions and minimize surface reconstructions
of the cathode. The inorganic-rich solid electrolyte interphase formed
on the hard carbon (HC) surface minimized undesirable reactions between
HC and the electrolyte. These stable interphases enabled high Coulombic
efficiency and long-term stable cycling of the HC anode and the NaCu1/9Ni2/9Fe1/3Mn1/3O2 cathode. The insights obtained in this work can be used to further
improve the cycling stability and safety of rechargeable batteries.
Sodium (Na)-ion batteries have been considered one of the most promising power sources beyond Li-ion batteries. Although the Na metal anode exhibits a high theoretical capacity of 1165 mAh g −1 , its application in Na batteries is largely hindered by dendrite growth and low coulombic efficiency. Herein, we demonstrate that an electrolyte consisting of 1 M sodium tetrafluoroborate in tetraglyme can enable excellent cycling efficiency (99.9 %) of a Na metal anode for more than 1000 cycles. This high reversibility of a Na anode can be attributed to a stable solid electrolyte interphase formed on the Na surface, as revealed by cryogenic transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). These electrolytes also enabled excellent cycling stability of Na||hard-carbon cells and Na||Na 2/3 Co 1/3 Mn 2/3 O 2 cells at high rates with very high coulombic efficiencies.
High-energy rechargeable lithium metal batteries have been intensively revisited in recent years. Since more researchers started to use pouch cell as the platform to study the fundamentals at relevant scales, safe testing and handling of lithium metal and high-energy lithium metal batteries have become critical. Cautions and safety procedures are needed when handling cycled pouch cells with pulverized lithium metal particles inside. From cell design, electrode preparation, cell fabrication to testing procedure, this work aims to discuss the possible root causes that may initiate cell internal short circuit and raise safety concerns. Safe transfer, disassembly and disposal of cycled Li metal pouch cells are also discussed. The insights provided in this article are applicable for the research on high-energy lithium-ion batteries as well and may inspire more safety strategies to accelerate research innovation by using large-format batteries as the testing vehicle and conduct the research safely.
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