Isotropous Sulfurized Polyacrylonitrile Interlayer with Homogeneous Na⁺ Flux Dynamics for Solid‐State Na Metal Batteries

Abstract

Inorganic solid‐state electrolyte (SSE) based Na‐metal batteries have received extensive attention in next‐generation lithium‐free energy storage systems with both high‐security and superior electrochemical performance. Herein, in contrast to the conventionally used polymer/ceramic/polymer sandwich electrolyte, an efficient green and scalable powder‐polishing synthetic method is developed to fabricate a pyrolyzed‐polyacrylonitrile modified Na super ionic conductor (NASICON) electrolyte to relieve polarization of integrated composite SSE and ameliorate interfacial contact between the electrolyte and the Na anode. Furthermore, introducing S in the preferable isotropous sulfurized polyacrylonitrile (SPAN) interlayer can trigger dehydrogenation and cyclization of polyacrylonitrile with chemically‐bonded short‐chain SS segments, which can bond with Na+ to redistribute the interfacial electric field and homogenize transported Na+ flux, leading to transition of Na deposition behavior from dendrite growth mode to lateral flat‐shape growth tendency. The conjugated polymer backbones possess delocalized radicals that can activate formed short‐chain sulfides to reconnect to the backbones, thus maintaining superior structural stability. Benefiting from the rational interfacial design, a record‐high value of 1.4 mA cm−2 for critical current density of Na/SPAN‐NASICON/Na cells is obtained. Moreover, SPAN is used as a cathode to assemble solid‐state Na/SPAN‐NASICON/SPAN Na‐organosulfur batteries, demonstrating superior capacity and cycling‐stability. The rational SPAN‐based structural design strategy may provide an avenue for potential application of solid‐state alkali metal batteries.

Optimizing the Na metal/solid electrolyte interface through a grain boundary design

“…GBS-NZSP, which is synthesized by an energy-saving lowtemperature sintering method and used without any post surface or chemical modication, exhibits excellent performance competitive with other solid electrolytes. 15,18,24,25,28,[35][36][37][38] A detailed comparison including the cell resistance, interfacial resistance, current density and stability is provided in Table S1 † to further signify the advantage and novelty of the well-designed GBS-NZSP solid electrolyte for sodium metal batteries.…”

Liquid Metal‐Organic Frameworks In‐Situ Derived Interlayer for High‐Performance Solid‐State Na‐Metal Batteries

“…Profiting from the interfacial optimization of liquid MOFs derived interlayer, the measured CCD in both capacity‐terminated and time‐terminated tests occupy the top level among reported NASICON‐based SSNBs in published literatures up to now (Figure 4g). [ 13,34–38 ] In addition, the symmetric Na/ZIF‐62‐650‐NASICON/Na cell also shows excellent long‐term RT galvanostatic cycling stability. As shown in Figure 4h, it delivers a stable cycling career for up to 1000 h at 0.1 mA cm −2 , while Na/NASICON/Na cell short‐circuited only after 22 cycles, which can also be verified from the EIS results of cycled cells (Figure S10a,b, Supporting Information).…”

“…Na 3 Zr 2 Si 2 PO 12 structured NASICON pellets were synthesized through a solid‐sintering procedure as previously reported. [ 13 ] Specifically, a stoichiometric combination of Na 2 CO 3 , ZrO 2 , SiO 2 , and NH 4 H 2 PO 4 was used as precursor, where the content of Na 2 CO 3 and NH 4 H 2 PO 4 were kept an excess of 15% to decrease ZrO 2 impurity. The mixture was first ball‐milled at 350 rpm for 24 h, followed by preheating at 1100 °C for 9 h and further pulverized by ball‐milling at 500 rpm for 2 h. Then, the collected power was pressed in a 16.0 mm mold under 400 MPa.…”

“…For example, Bruce's group [ 12 ] imaged Na dendrites with crack morphology in β″‐Al 2 O 3 SSE, and our group observed vertical Na dendrites in cycled Na/Na super ionic conductor (NASICON) interface. [ 13 ] However, the formation mechanisms and morphology varieties of Na dendrites among solid‐state Na‐metal batteries (SSNBs) are still indistinct and only taken as analogues of Li dendrites counterparts until now. Considering that metallic Na is more ductile and demonstrates much higher chemical reactivity than Li, coupled with its different standard electrode potentials, [ 14 ] the growth processes of Na dendrites among SSNBs are supposed as compositive and characteristic behaviors.…”

“…[ 17,20 ] Although cost‐effective liquid coating precursor solution can realize intimate soaking of SSEs, the obtained coating‐layer shows inferior surface coverage and poor affinity with beneath SSE due to subsequent solvent evaporation and solute recrystallization processes. [ 13 ] Developing suitable processing methods to prepare compact/uniform active sites‐matrix mixed conductive interlayer on SSEs is urgently needed.…”