Na–K Alloy Anode for High-Performance Solid-State Sodium Metal Batteries

Abstract

Rechargeable solid-state Na metal batteries (SSNMB) can offer high operational safety and energy density. However, poor solid−solid contact between the electrodes and the electrolyte can dramatically increase interfacial resistance and Na dendrite formation, even at low current rates. Therefore, we developed a carbon-fiber-supported liquid Na−K alloy anode that ensures close anode−electrolyte contact, enabling superior cycle stability and rate capability. We then demonstrated the first cryogenic transmission electron microscopy (cryo-TEM) characterization of an SSNMB, capturing the evolution of solid− electrolyte interphase (SEI) and revealing both crystalline and amorphous phases, which could facilitate ion transport and prevent continuous side reactions. By enhancing contact between the Na− K alloy and solid-state electrolyte, these symmetric cells are capable of cycling for over 800 h without notable increased polarization and enable an unprecedented critical current density (CCD) at 40 mA cm −2 . Our liquid Na−K alloy approach offers a promising strategic avenue toward commercial SSNMBs.

Inorganic All‐Solid‐State Sodium Batteries: Electrolyte Designing and Interface Engineering

“…designed a novel Na–K alloy anode supported by carbon nanofibers, which improved the tightness between anode and solid electrolyte and thus prevent dendrite growth at the interface (Figure 9e). [ 162 ] In their work, the cryogenic transmission electron microscopy characterization was for the first time used to direct the evolution of solid electrolyte interphase (SEI), confirming that the highly chemical/electrochemically stable Na 2 O and ionic conductive NaPO 3 and Na 4 P 2 O 7 were formed on the surface of solid electrolyte. Based on these, the liquid Na–K alloy anode achieved intimate contact with solid electrolyte, while there are distinct gaps at the interface for pure Na metal anode.…”

“…Reproduced with permission. [ 162 ] Copyright 2022, American Chemical Society. f) Schematic illustrating the interfacial contact behavior between the NZSP (Au‐NZSP) and Na metal.…”

“…e) Na||ZNSE and Na-K||ZNSE interfaces. Reproduced with permission [162]. Copyright 2022, American Chemical Society.…”

Recent advances of structural/interfacial engineering for Na metal anode protection in liquid/solid-state electrolytes

“…Cheng et al annealed Na–K alloy to attach the carbon fiber at 750 °C to obtain the carbon-fiber-supported liquid Na–K alloy. 165 The carbon fiber would generate flaws on the structure after high temperature treatment, increasing its affinity with Na–K alloy (record as ZNSE). The alloy electrode and NASICON were joined at a pressure of 50 MPa, and the Na–K alloy was entirely bonded to the SSEs with no visible cracks or dendrites.…”

Ultrastable Sodium/Potassium Metal Anode Enabled by a Multifunctional Interphase Layer with Enhanced Ion Transport Kinetics

“…[15,16] However, uncontrolled dendrites growth of Na (K) and instable Na (K) electrode/electrolyte interface result from the electrochemical reaction between the high electrochemical activity of Na (K) metal and electrolyte, which seriously inhibits the development of NMB (KMB). [17][18][19][20] Recently, much effort has been devoted to addressing these issues of Na (K) metal anode, such as constructing a 3D collector host to decrease the local current density and accommodate the vast volume expansion of Na (K) metal, [21][22][23][24][25][26] electrolyte manipulation to regulate the solvation structure of Na + and enhance the interfacial charge transfer kinetics, [27][28][29][30] and artificial solid electrolyte interphase (SEI) implantation to stabilize the electrode/electrolyte interface and induce uniform Na (K) deposition. [31][32][33] Among them, building an ideal SEI on the Na (K) anode surface has been demonstrated as one of the most effective strategies.…”