Dynamic Electrode–Electrolyte Intermixing in Solid-State Sodium Nano-Batteries

Abstract

Nanostructured solid-state batteries (SSBs) are poised to meet the demands of next-generation energy storage technologies by realizing performance competitive to their liquidbased counterparts while simultaneously offering improved safety and expanded form factors. Atomic layer deposition (ALD) is among the tools essential to fabricate nanostructured devices with challenging aspect ratios. Here, we report the fabrication and electrochemical testing of the first nanoscale sodium all-solid-state battery (SSB) using ALD to deposit both the V 2 O 5 cathode and NaPON solid electrolyte followed by evaporation of a thin-film Na metal anode. NaPON exhibits remarkable stability against evaporated Na metal, showing no electrolyte breakdown or significant interphase formation in the voltage range of 0.05−6.0 V vs Na/Na + . Electrochemical analysis of the SSB suggests intermixing of the NaPON/V 2 O 5 layers during fabrication, which we investigate in three ways: in situ spectroscopic ellipsometry, time-resolved X-ray photoelectron spectroscopy (XPS) depth profiling, and cross-sectional cryo-scanning transmission electron microscopy (cryo-STEM) coupled with electron energy loss spectroscopy (EELS). We characterize the interfacial reaction during the ALD NaPON deposition on V 2 O 5 to be twofold: (1) reduction of V 2 O 5 to VO 2 and (2) Na + insertion into VO 2 to form Na x VO 2 . Despite the intermixing of NaPON−V 2 O 5 , we demonstrate that NaPONcoated V 2 O 5 electrodes display enhanced electrochemical cycling stability in liquid-electrolyte coin cells through the formation of a stable electrolyte interphase. In all-SSBs, the Na metal evaporation process is found to intensify the intermixing reaction, resulting in the irreversible formation of mixed interphases between discrete battery layers. Despite this graded composition, the SSB can operate for over 100 charge−discharge cycles at room temperature and represents the first demonstration of a functional thin-film solid-state sodium-ion battery.

Unveiling the recent advances in micro-electrode materials and configurations for sodium-ion micro-batteries

“…50–55 It is important to note that Na-ions have a weaker interaction with solvent and a smaller solvation shell compared to Li ions, resulting in a hydrated ionic radius of 1.84 Å for Na and 2.38 Å for Li. 56–58 The faster diffusion kinetics of Na ions contributes to the high-power SIμB, resulting in a fast charge–discharge rate. Furthermore, the high charge-to-mass ratio of ions, in accordance with Faraday's law of electrolysis, is beneficial for achieving a high gravimetric capacity.…”

Simultaneous Solid Electrolyte Deposition and Cathode Lithiation for Thin Film Batteries and Lithium Iontronic Devices

“…27 Prelithiation of the V 2 O 5 cathode makes any contribution of Li from LiPON difficult to distinguish. Recent work by Nuwayhid et al found intermixing of atomic layer deposition NaPON onto V 2 O 5 caused significant intermixing, 40 indicating that this phenomenon may not be limited to sputtering or to lithium.…”