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.

Thermal Stability of High Power 26650-Type Cylindrical Na-Ion Batteries

As a new electrochemical power system,safety(especially thermal safety)of Na-ion batteries(NIBs)is the key towards large-scale industrialization and market application.Thus,research on the thermal stability of NIBs is helpful to evaluate the safety properties and to provide effective strategies to prevent the occurrence of battery safety failure.Thermal stability of the high-power 26650 cylindrical NIBs using Cu-based layered oxide cathode and hard carbon anode is studied.The high power NIBs can achieve fast charge and discharge at 5–10 C rate and maintain 80%capacity after 4729 cycles at 2 C/2 C rate,where the unit C denotes a measure of the rate at which a battery is charge-discharged relative to its maximum capacity.The results of accelerating rate calorimeter and differential scanning calorimetry(ARC-DSC)test results show that NIBs have a higher initial decomposition temperature(≥110℃)and a lower maximum thermal runaway temperature(≤350℃)than those of Li-ion batteries(LIBs),exhibiting a favorable thermal stability.It should be noted that the heat generation of cathode accounts for a large proportion of the total heat generation while the thermal stability of the anode determines the initial thermal runaway temperature,which is similar to LIBs.Finally,the whole temperature characteristics of the NIBs in the range of−60℃–1000℃are summarized,which provide guidance for the safety design and applications of NIBs.