Highly Oxidation‐Resistant Electrolyte for 4.7 V Sodium Metal Batteries Enabled by Anion/Cation Solvation Engineering

Abstract

Sodium metal batteries (SMBs) are considered as promising battery system due to abundant Na sources. However, poor compatibility between electrolyte and cathode severely impedes its development. Herein, we proposed an anion/cation solvation strategy for realizing 4.7 V resistant SMBs electrolyte with NaClO4 and trimethoxy(pentafluorophenyl)silane (TPFS) as dual additives (DA). The ClO4− can rapidly transfer to the cathode surface and strongly coordinate with Na+ to form stable polymer‐like chains with solvents. Meanwhile, TPFS can preferentially enter into the PF6− anion solvation sheath for reducing PF6‐solvent interaction and effectively scavenge adverse electrolyte species for protecting electrode electrolyte interphases. Thus, such electrolyte elevates the oxidative stability of carbonate electrolytes from 3.77 to 4.75 V, and enables Na||Na3V2(PO4)2O2F (NVPF) battery with a capacity retention of 93 % and an average Coulombic efficiency (CE) of 99.6 % after 500 cycles at 4.7 V.

Weak Solvent–Solvent Interaction Enables High Stability of Battery Electrolyte

“…In this way, the redox properties of the electrolyte components, including solvent, additive, and anion during the polarization, − as well as the recently proposed M + –solvent–anion complex formed during the desolvation process on the electrode surface, − have been widely studied to evaluate the electrolyte, since they can be highly influenced by the widely existing electrostatic interactions between M + , anions, and solvent molecules with uneven charge distribution. Then, varying the interactions of M + –solvent, M + –anion pair, and anion–solvent by changing the type and quantity of solvents, anions, additives, etc., have received significant attention recently to tune the electrolyte properties. − It is worth noting that solvent–solvent interaction has rarely been mentioned before, as such interaction is considered to be very weak, 1–2 orders of magnitude weaker than the ion–ion interaction between M + –anion and the ion-dipole interaction between M + –solvent . However, it is still necessary to make clear the effect of solvent–solvent interactions, as the molar quantity of solvent in the commercial electrolyte is always 10–12 times higher than that of cation and anion when electrolyte with a concentration of 1 M was used. − Therefore, whether the strength of this weak solvent–solvent interaction is sufficient to affect the performance of the electrolyte needs to be paid attention to.…”

Construction of Inorganic-Rich Cathode Electrolyte Interphase on Co-Free Cathodes

“…Therefore, the construction of the stable CEI on the cathode is crucial for improvement of the cycle performance of Li-rich cathodes. According to recent research, the texture and composition of CEI are critical for the stability of the cathode. − Particularly, the addition of various functional additives to conventional electrolytes to modify the structure of CEI, consequently boosting the cycling performance and rate capability of cathode materials, has been widely explored. − Since the HOMO energy of the additive is higher than that of the solvent, it is oxidized on the cathode surface earlier than the solvent, forming a thin and dense inorganic-rich CEI that improved the Li + ion conductivity and thermal stability, reduced the interfacial impedance, and thus enhanced the electrochemical performance of LIBs. , For instance, Hu and co-workers reported that a protective CEI consisting of Li 3 PO 4 and LiF, the decomposition products of the additive of lithium difluorophosphate, can reduce TM dissolution and relieve surface reconstruction. Nevertheless, the formation mechanism and chemistry of CEI are still unclear, and it is in a dynamic evolution process upon cycling, which primarily relies on speculation and indirect proof. ,− Therefore, how to optimize the CEI structure and the orient formation of robust CEI is a rather challenging task.…”

Magnetoelectric synergy strategy for superior iron disulfide anode

“…41–44 Moreover, a Lorentz force-assisted MHD effect over the FeS 2 complex can promote convective Na + transfer within the electrolyte, to give a uniform Na + flux, which is beneficial for homogeneous deposition of Na + , and thus prevents the growth of Na dendrites and improves the stability of the SEI layer. 45–48…”

“…[41][42][43][44] Moreover, a Lorentz forceassisted MHD effect over the FeS 2 complex can promote convective Na + transfer within the electrolyte, to give a uniform Na + flux, which is beneficial for homogeneous deposition of Na + , and thus prevents the growth of Na dendrites and improves the stability of the SEI layer. [45][46][47][48] In this work, FeS 2 nanoparticles wrapped within highly conductive porous carbon spheres enclosed by thin nanosheets (NSs)VS 2 were deliberately constructed for Na + storage, in which high-density edge sites and dangling sites endow the structure with promoted sodium storage performance. The pores that exist within the FeS 2 stacked nanoparticles and VS 2 nanoflowers greatly increase the active specific surface area and accelerate electrolyte infiltration.…”