Modification of NASICON Electrolyte and Its Application in Real Na-Ion Cells

The low ionic conductivity of solid-state electrolytes(SSEs)and the inferior interfacial reliability between SSEs and solid-state electrodes are two urgent challenges hindering the application of solid-state sodium batteries(SSSBs).Herein,sodium(Na)super ionic conductor(NASICON)-type SSEs with a nominal composition of Na_(3+2x)Zr_(2-x)MgxSi_(2)PO_(12) were synthesized using a facile two-step solid-state method,among which Na_(3.3)Zr_(1.85)Mg_(0.15)Si_(2)PO_(12)(x=0.15,NZSP-Mg_(0.15))showed the highest ionic conductivity of 3.54mS∙cm^(-1) at 25℃.By means of a thorough investigation,it was verified that the composition of the grain boundary plays a crucial role in determining the total ionic conductivity of NASICON.Furthermore,due to a lack of examination in the literature regarding whether NASICON can provide enough anodic electrochemical stability to enable high-voltage SSSBs,we first adopted a high-voltage Na_(3)(VOPO_(4))2F(NVOPF)cathode to verify its compatibility with the optimized NZSP-Mg_(0.15) SSE.By comparing the electrochemical performance of cells with different configurations(low-voltage cathode vs high-voltage cathode,liquid electrolytes vs SSEs),along with an X-ray photoelectron spectroscopy evaluation of the after-cycled NZSP-Mg_(0.15),it was demonstrated that the NASICON SSEs are not stable enough under high voltage,suggesting the importance of investigating the interface between the NASICON SSEs and high-voltage cathodes.Furthermore,by coating NZSP-Mg_(0.15) NASICON powder onto a polyethylene(PE)separator(PE@NASICON),a 2.42 A∙h non-aqueous Na-ion cell of carbon|PE@NASICON|NaNi_(2/9)Cu_(1/9)Fe_(1/3)Mn_(1/3)O_(2) was found to deliver an excellent cycling performance with an 88%capacity retention after 2000 cycles,thereby demonstrating the high reliability of SSEs with NASICON-coated separator.

Hunting Sodium Dendrites in NASICON-BasedSolid-State Electrolytes

NASICON-(Na superionic conductor-)based solid-state electrolytes(SSEs)are believed to be attracting candidates for solid-state sodium batteries due to their high ionic conductivity and prospectively reliable stability.However,the poor interface compatibility and the formation of Na dendrites inhibit their practical application.Herein,we directly observed the propagation of Na dendrites through NASICON-based Na3.1Zr2Si2.1P0.9O12 SSE for the first time.Moreover,a fluorinated amorphous carbon(FAC)interfacial layer on the ceramic surface was simply developed by in situ carbonization of PVDF to improve the compatibility between Na metal and SSEs.Surprisingly,Na dendrites were effectively suppressed due to the formation of NaF in the interface when molten Na metal contacts with the FAC layer.Benefiting from the optimized interface,both the Na||Na symmetric cells and Na3V2(PO4)3||Na solidstate sodium batteries deliver remarkably electrochemical stability.These results offer benign reference to the maturation of NASICON-based solid-state sodium batteries.