A NASICON-type electrolyte was considered to be one of the most promising electrolytes for solid-state Na metal batteries. However, its lower ion conductivity compared to a liquid electrolyte and the formation of Na dendrites hinder its practical application. Herein, NASICON-type (Na3Zr2Si2PO12) solid-state electrolytes with developed ionic conductivity and declined electronic conductivity were synthesized through the rare earth oxide-assisted sintering method, such as Sm2O3 and Ho2O3. With the presence of Sm2O3 and Ho2O3 during sintering, the formed phosphate grain boundary phase adjusts the Si/P ratio in the NASICON structure with higher Na+ occupancy and then enhances the ionic conductivity of electrolytes. On the other hand, the formed phosphate grain boundary phase with low electronic conductivity prevents the movement of electrons at the grain boundary, reducing the probability that electrons combine with Na+ at the grain boundary to form Na0, thereby restricting the formation of dendrites along grain boundaries. In addition, the added Sm2O3 and Ho2O3 play the role of fluxing agents to increase the densification of ceramics, further enabling the enhancement of ionic conductivity and restriction of dendrites in the voids. As a result, the obtained NZSP-0.2Sm and NZSP-0.3Ho electrolytes deliver critical current density (CCD) values of 0.85 and 0.65 mA cm–2, respectively, at room temperature. Application of the obtained electrolytes in Na metal batteries is evaluated by assembling Na3V2(PO4)3|NZSP-0.2Sm/0.3Ho|Na cells, which deliver high discharge capacity values of 102.6 and 101.8 mAh g–1 at 0.5 C after 100 cycles with capacity retention ratios of 98.3 and 98.6%, respectively. The presented results indicated that rare earth oxide-assisted sintering is an effective route to improve the ionic conductivity and restrict dendrite formation for oxide ceramic solid-state electrolytes.

Solid-state sodium metal batteries using non-flammable solid-state electrolytes are recognized as next-generation energy storage technology in view of their merits of high safety and low cost. However, the lower ion conductivity (below the application requirements of 10−3 S cm−1) and interface issues that exist in electrolytes/electrodes for most solid-state electrolytes hinder their practical application. In this paper, NASICON-type Na3Zr2Si2PO12 (NZSP) electrolytes with enhanced ion conductivity are synthesized by the Bi2O3-assisted sintering method. The influence of the Bi2O3 sintering agent content on the crystalline phase, microstructure, density and ion conductivity as well as the electrochemical performances applied in batteries for the obtained NZSP electrolytes are investigated in detail. With the presence of Bi2O3, the formed Na3Bi(PO4)2 impurity increased the Si/P ratio in the NASICON structure with higher Na+ occupancy, then enhanced the ionic conductivity to a level of 1.27 × 10−3 S cm−1. Unfortunately, the Bi2O3-assisted sintered NZSP shows a degradation in the cycling stability when applied to solid-state sodium batteries because of the decreased interfacial stability with Na anodes. The formation of a Bi-Na alloy during cycling might be conducive to Na dendrite growth in electrolytes, degrading the cycling performance. This work presents a facial method to improve the ion conductivity of NASICON-type electrolytes and gives insight into the interface issues of solid-state sodium metal batteries.

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Considering the deficiency in milling process parameters selection in the domestic. Based on the modeling of dynamic milling force and the calculate of chatter stability limits. Realizing high speed milling regeneration type chatter simulation algorithm with Matlab development tools. Through the modal hammer experiment, Obtaining the frequency response function to simulate the chatter stability domain graphics of the whole processing system which can be used as an instruction guide for the selection of milling process parameters. The validation and accuracy of the simulation algorithm was verified by experiments and used in a factory with an excellent application effect.