Elastic and Plastic Characteristics of Sodium Metal

Abstract

Sodium metal holds promise as an anode material for rechargeable batteries due to its large theoretical charging capacity, low electrochemical potential, earth abundance, and low cost. However, a number of concerns remain that must be addressed prior to practical implementation, particularly Na's propensity to form unstable morphologies during electrochemical deposition. Given the importance of mechanical deformation in this process, unlocking the potential of sodium metal as an anode material requires a thorough understanding of its mechanical properties. To this end, we evaluate the mechanical properties of sodium metal at room temperature through a combination of bulk compression, microhardness, and nanoindentation tests. With regard to elastic properties, nanoindentation testing produced an elastic modulus of 3.9 ± 0.5 GPa. With regard to plastic properties, bulk compression testing revealed the flow stress at 0.08 strain as varying between 102 and 254 kPa at strain rates between 10 −4 and 10 −2 s −1 . Nanoindentation indicated a decrease in hardness from 26.6 to 2.3 MPa at target P ̇/P = 0.05 s −1 as the indentation depth increased from 0.25 to 10 μm, while microhardness testing indicated hardness values between 1.6 and 1.1 MPa at depths varying between 50 and 130 μm. We perform finite element simulations to relate length scales in these measurements (e.g., depth) to physical lengths scales relevant to battery applications. We also found that Na exhibits a marked strain-rate sensitivity, with a strainrate sensitivity exponent of m = 0.14 from nanoindentation and m = 0.20 from bulk compression. Likewise, indentation demonstrated that Na is even more susceptible to creep than is Li metal. Overall, our studies indicate that Na metal is extremely soft, readily creeps, and exhibits pronounced size effects. We discuss the implications of these properties relative to other candidate anode materials of rechargeable batteries. Most notably, Na's greater propensity to creep than Li, in turn, has implications for charging rate capability in solid-state batteries.

Electrolytes and Interphases in Sodium‐Based Rechargeable Batteries: Recent Advances and Perspectives

“…The use of sodium metal as the negative electrode grants high theoretical specific capacity (1166 mAh g −1 ) and low redox potential (−2.714 V vs SHE), [ 269–273 ] yielding to high energy batteries. In order to exploit these benefits in Na‐metal batteries such as Na–O 2 , [ 274–276 ] Na–S, [ 277,278 ] and Na–CO 2 , [ 279 ] the challenges related to dendritic metal growth and unwanted parasitic reactions at the electrode/electrolyte interphase need to be addressed.…”

A review on recent approaches for designing the SEI layer on sodium metal anodes

“…Although the high mechanical modulus of lithium dendrites cannot be effectively suppressed by engineering the SEI layer, the low mechanical modulus of sodium enables the fabrication of a robust SEI layer, thereby posing a promising technology. 64 This review provides a meaningful insight to promote the artificial engineering of the SEI layer for progressive applications in SMBs (Fig. 4).…”

Self‐Waveguide Single‐Benzene Organic Crystal with Ultralow‐Temperature Elasticity as a Potential Flexible Material

“…The establishment of ultralow temperature flexible materials system as well as optimization of mechanical properties and luminescent functions will not only reduce the load demand of low temperature environments but also may expand the functional applications of flexible materials. The flexibilities of current materials are generally based on the chain movement of polymers or the toughness of metals [5–11] . However, metals usually have large mechanical strength and their flexibilities will become poorer at low temperature due to the limitation of the motion of atoms [12, 13] .…”

“…The flexibilities of current materials are generally based on the chain movement of polymers or the toughness of metals. [5][6][7][8][9][10][11] However, metals usually have large mechanical strength and their flexibilities will become poorer at low temperature due to the limitation of the motion of atoms. [12,13] Polymers exhibit excellent flexibilities at room temperature (r.t.), however, they are quite brittle at ultralow temperatures.…”