Nasicon Electrolytes Research Articles

Calcium Doped NASICON Electrolyte with Graphite Coating for Stable All-solid-state Sodium Metal Batteries.

All-solid-state sodium metal batteries face the challenges of low ionic conductivity of solid electrolytes and poor wettability towards metallic Na anode. Herein, Na3Zr2Si2PO12 solid electrolyte is doped with Ca2+, obtaining a high ionic conductivity of 2.09×10-3 S cm-1 with low electronic conductivity of 1.43×10-8 S cm-1 at room temperature, which could accelerate Na+ transportation and suppress sodium dendrite growth. Meanwhile, a graphite-based interface layer is coated on Na3.4Zr1.8Ca0.2Si2PO12 (Na3.4Zr1.8Ca0.2Si2PO12-G) in order to improve the solid-solid contact between solid electrolyte and Na anode, realizing a uniform current distribution and smooth Na metal plating/stripping, and thus achieving a triple higher critical current density of 3.5 mA cm-2 compared with that of Na3.4Zr1.8Ca0.2Si2PO12. In addition, the assembled Na3V2(PO4)3/Na3.4Zr1.8Ca0.2Si2PO12-G/Na all-solid-state battery exhibits excellent electrochemical performances with a reversible capacity of 81.47 mAh g-1 at 1 C and capacity retention of 97.75 % after 500 cycles.

Ruthenium doping of NASICON electrolyte augments the performance of solid-state sodium-ion batteries

Recently remarkably high ionic conductivities (up to 5.5 x 10-3 Ω-1cm−1) at 25 °C have been achieved in sodium superionic conducting (NASICON) solid-state electrolytes via aliovalent cation doping. Doping in NASICON leverages the synergic effects of bottleneck opening (lattice expansion) and correlated migration (higher carrier concentration). However, there is no report published that isolates the effect of correlated migration induced by heterovalent doping without the influence of structural/bottleneck changes. Therefore, here we report for the first time the substitution of trivalent Ru3+ cation into the Zr4+ site to enhance the ionic conductivity of the NASICON electrolyte. Even though Ru3+ has a smaller ionic radius than Zr4+ and leads to bottleneck shrinkage, high ionic conductivity is achieved on doping Ru as compared to undoped NZSP. Using first-principles calculations, we show that even though the bottleneck for Na+ migration shrinks, the diffusion barriers are nearly the same owing to the weaker Na-framework interaction. The doped electrolyte showed an ionic conductivity of 2.1 x 10-3 Ω-1cm−1, an ionic transference number of ∼ 98.9 %, and exhibited stable sodium plating/stripping at 0.5 mA-cm−2 for 100 h with an overpotential of 20 mV owing to the fused microstructure. The assembled all-solid-state battery with Ru-doped electrolyte exhibited an outstanding initial capacity of 87 mAh-g−1 at 0.3C as compared to 70 mAh-g−1 with undoped electrolyte. Compared to the pristine sample, which had capacity retention of 60 % after 100 cycles, the cell containing Ru-doped electrolyte demonstrated stable cycling with an 87 % capacity retention without external pressure.

In Situ Forming Na─Sn Alloy/Na2S Interface Layer for Ultrastable Solid State Sodium Batteries

AbstractThe poor interfacial compatibility between sodium superionic conductor (NASICON) electrolyte and metallic sodium anode will lead to severe dendrite penetration, impeding the application of NASICON electrolytes for solid state sodium batteries. Herein, a homogeneous SnS2 coating layer is sputtered on the surface of Na3.4Zn0.1Zr1.9Si2.2P0.8O12 electrolyte to in situ construct a kinetically stable Na─Sn alloy/Na2S interlayer, possessing superior Na affinity, low diffusion barrier, and electronic insulating character to suppress dendrite growth, which is confirmed by experiments and density‐functional theory calculations. Benefiting from the Na─Sn alloy/Na2S interphase, the critical current density of Na3.4Zn0.1Zr1.9Si2.2P0.8O12 increases from 2.4 to 9.4 mA cm−2. In addition, the obtained Na3V2(PO4)3/Na3.4Zn0.1Zr1.9Si2.2P0.8O12@SnS2/Na solid state batteries exhibit a high initial reversible discharge capacity of 115.1 mAh g−1 at 0.1 °C with an initial Coulombic efficiency of 93.6%, and a capacity retention rate of 88.1% after 1000 cycles at 1 C.

Pottery glaze-derived sintering aids for the synthesis of NASICON electrolytes with high ionic conductivity and relative density

The glaze component is successfully utilized as a sintering aid to obtain a NASICON with high Na+ conductivity and relative density.

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

Inorganic all-solid-state sodium batteries (IASSSBs) are emerged as promising candidates to replace commercial lithium-ion batteries in large-scale energy storage systems due to their potential advantages, such as abundant raw materials, robust safety, low price, high-energy density, favorable reliability and stability. Inorganic sodium solid electrolytes (ISSEs) are an indispensable component of IASSSBs, gaining significant attention. Herein, this review begins by discussing the fundamentals of ISSEs, including their ionic conductivity, mechanical property, chemical and electrochemical stabilities. It then presents the crystal structures of advanced ISSEs (e.g., β/β''-alumina, NASICON, sulfides, complex hydride and halide electrolytes) and the related issues, along with corresponding modification strategies. The review also outlines effective approaches for forming intimate interfaces between ISSEs and working electrodes. Finally, current challenges and critical perspectives for the potential developments and possible directions to improve interfacial contacts for future practical applications of ISSEs are highlighted. This comprehensive review aims to advance the understanding and development of next-generation rechargeable IASSSBs.

NaF-Rich Multifunctional Layers toward Stable All-Solid-State Sodium Batteries.

NASICON oxide solid electrolytes are considered promising candidates for all-solid-state sodium batteries due to their extremely high ionic conductivity and favorable electrochemical stability. However, the practical application of NASICON electrolytes is greatly impeded by poor electrolyte-electrode interfacial contact and continuous sodium dendrite propagation. Herein, a NaF-rich multifunctional interface layer on the surface of a Na anode (Na@NaF-rich), containing NaF, amorphous carbon, and an unreacted C-F bond species, is developed in situ by the reaction between Na and commercial poly(tetrafluoroethylene). This NaF-rich interface layer is proven to reduce the diffusion barriers at the Na/NASICON electrolyte interface and homogenize Na deposition as well as suppress Na dendrite growth, thus achieving a high critical current density of 4 mA cm-2. The resultant Na3V2(PO4)3@C/Na@NaF-rich all-solid-state cell showed a high initial specific capacity of 117.6 mAh g-1 at 0.1 C with a Coulombic efficiency of 94.8%. Even at 0.5 and 1 C, it still exhibited high capacity retentions of 83.3% and 80.4%, respectively, after 750 cycles.

Machine Learning Guided Cobalt‐doping Strategy for Solid‐state NASICON Electrolytes

AbstractThe solid‐state battery (SSB) is a promising direction to address the inherent safety problems in commercial batteries and energy storage systems. However, the development of SSBs is still hider of the low ionic conductivity of solid‐state electrolytes. Based on a machine learning (ML) method, a cobalt‐doping strategy was developed for the Na3.2Zr2Si2.2P0.8O12 (NASICON) compound by training on NASICON‐type solid electrolyte data. The cobalt‐doping strategy efficiently improves the NASICONs’ ionic conductivity to ~2.63 mS/cm with low activation energy at ~0.245 eV. The grain‐boundary ionic conductivity reaches ~11.00 mS/cm without extra densification of the pellet. The NASICON's structures were studied by the Rietveld and the bond‐valence methods. The calculations and observed structural transitions confirm that the cobalt‐doping strategy promotes the structural transition and adjusts the structure to a better performance state. The doping strategy predicted by the ML model is consistent with our experimental results, providing very useful guidance for improving ionic conductivity of NASICON electrolytes.

Improved ion conductivity and interface characteristics of the Te-doped solid NASICON electrolyte Li1.5Al0.5Ge1.5(PO4)3 with graphite coating

Solid Te-doped Li1.5Al0.5TexGe1.5-x(PO4)3 (LATGP) electrolyte materials are successfully prepared by the sol-gel method. The structure, morphology, and ionic and electronic conductivities of samples with different doping concentrations are analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and DC polarization. The results reveal that Te doping can effectively promote the ionic conductivity of LAGP material, reaching a value of 6.33 × 10−4 S cm−1 at room temperature for Li1.5Al0.5Te0.06Ge1.44(PO4)3. Then, LATGP sheets are coated with graphite (G) by the magnetron sputtering method to improve the interfacial characteristics between the Li metal and LAGP electrolyte at high current densities. The polarization voltage curves of the symmetric graphite-modified Li/G@LATGP@G/Li cells remain stable after 800 h at high current densities of 0.5 mA cm−2 and 1 mA cm−2. The solid-state Li/G@LATGP/LiFePO4 full cell presents an initial specific discharge capacity of 154.4 mAh·g−1 at a current density of 0.1 mA cm−2 as well as a capacity retention of 87.8% after 100 cycles. These results indicate that Te doping combined with graphite surface coating can effectively improve the ion transport and interfacial characteristics of solid LAGP electrolyte.

Engineered Grain Boundary Enables the Room Temperature Solid-State Sodium Metal Batteries

The NASICON-type (Sodium Super Ionic Conductor) Na3Zr2Si2PO12 solid electrolyte is one of the most promising electrolytes for solid-state sodium metal batteries. When preparing Na3Zr2Si2PO12 ceramic using a traditional high-temperature solid-state reaction, the high-densification temperature would result in the volatilization of certain elements and the consequent generation of impurity phase, worsening the functional and mechanical performance of the NASICON electrolyte. We rationally introduced the sintering additive B2O3 to the NASICON matrix and systemically investigated the influence of B2O3 on the crystal structure, microstructure, electrical performance, and electrochemical performance of the NASICON electrolytes. The results reveal that B2O3 can effectively reduce the densification sintering temperature and promote the performance of the Na3Zr2Si2PO12 electrolyte. The Na3Zr2Si2PO12-2%B2O3-1150 ℃ achieves the highest ionic conductivity of 4.7 × 10−4 S cm−1 (at 25 °C) with an activation energy of 0.33 eV. Furthermore, the grain boundary phase formed during the sintering process could improve the mechanical behavior of the grain boundary and inhibit the propagation of metallic sodium dendrite within the NASICON electrolyte. The assembled Na/Na3Zr2Si2PO12-2%B2O3/Na3V1.5Cr0.5(PO4)3 cell reveals the initial discharge capacity of 98.5 mAh g−1 with an initial Coulombic efficiency of 84.14% and shows a capacity retention of 70.3% at 30 mA g−1 over 200 cycles.

Screening of Sintering Aids for Oxide Ceramics: A Case of NASICON Electrolyte.

In this work, an efficient screening method to select appropriate sintering aids for a wide range of oxide material systems is developed. Consequently, Na2 B4 O7 , NaF, and CuO are selected as sintering aids for sodium super ionic conductor(NASICON)-type Na3 Zr2 Si2 PO12 ceramic to verify the feasibility of the as-proposed method. As evidenced by the results, the sinterability and densification of ceramic matrix are apparently improved. Specifically, Na3 Zr2 Si2 PO12 -7%Na2 B4 O7 , Na3 Zr2 Si2 PO12 -3%NaF, and Na3 Zr2 Si2 PO12 -3%CuO endow much higher room temperature ionic conductivity of 1.03×10-3 , 1.61×10-3 , and 1.63×10-3 Scm-1 , respectively, in comparison with the pristine (7.23×10-4 Scm-1 ). The underlying mechanism for the enhanced performance is also discussed. The symmetric sodium cells assembled with sintering aids modified Na3 Zr2 Si2 PO12 ceramic electrolyte exhibit ultra-stable metallic Na plating/stripping at room temperature. Moreover, solid-state sodium batteries paired with Na3 V1.5 Cr0.5 (PO4 )3 cathode active material and modified Na3 Zr2 Si2 PO12 ceramic electrolyte demonstrate superior cycling stability and excellent rate capability. Furthermore, an as-developed strategy can be universally extended to synthesize high-performance oxide ceramics.

Enhanced electrochemical properties of NASICON-type Na3Zr2Si2PO12 solid electrolytes with Tb3+-ions-assisted sintering

The new-type NZSP solid-state electrolytes with enhanced ion transport properties were synthesized by using lanthanide rare-earth Tb3+ ions assisted-sintering. The Na3+xZr2-xTbxSi2PO12 (x = 0, 0.1, 0.2, 0.3, 0.4) solid-state electrolytes were characterized by X-ray diffraction analysis, scanning electron microscopy, and AC impedance testing. The effects of different Tb3+ contents on the phase composition, microstructure morphology, and electrochemical performance were investigated. The results showed that both Na3Zr2Si2PO12 and Na3Tb(PO4)2 phases are formed in the solid electrolytes by Tb3+-ions-assisted sintering. The formation of a new phosphate phase regulates the Si/P ratio of the dominant electric phase, enhances the Na+ occupation, and helps to enhance the mobility of sodium ions. The introduction of an appropriate amount of Tb3+ ions has a soldering-like effect, which can effectively improve the densification of ceramics and further improve the ionic conductivity by promoting grain fusion and reducing the grain boundary concentration. At room temperature, the ceramic with the composition Na3.2Zr1.8Tb0.2Si2PO12 exhibits a high relative density of 97.03% and the highest ionic conductivity of 6.32 × 10−4 S·cm−1 and with a low activation energy of 0.22 eV. In addition, the Na3Tb(PO4)2 grain boundaries phase with low electronic conductivity can limit the transfer of electrons and reduce the electronic conductivity of the NASICON electrolytes, so that the tolerance of solid-state electrolytes against Na dendrite growth is strongly enhanced. The Tb3+-ion-assisted sintering strategy can provide a valuable reference for improving the electrochemical performance of fast ion conductors.

Stabilizing the NASICON Solid Electrolyte in an Inert Atmosphere as a Function of Physical Properties and Sintering Conditions for Solid-State Battery Fabrication

The interfacial contact between a solid electrolyte and cathode materials is one of the challenges for the solid-state battery (SSB) industry. The cosintering of a solid electrolyte and cathode materials could be a possible solution. Considering the future scope of solid-state battery fabrication by the cosintering process of phosphate-based solid electrolytes and phosphate-based cathodes (LiFePO4, Li3V2(PO4)3, etc.), the present study focuses on stabilizing the NASICON structured Li1.4Al0.4Ti1.6(PO4)3 (LATP) solid electrolyte in an inert atmosphere as proposed cathode materials are not stable in air at high temperatures. The results show a high influence of particle size and heating rate along with sintering temperature on achieving a pure phase and fully dense pellets in an argon atmosphere. Cracks/voids, secondary phases, and reduction of Ti were observed in pellets prepared with a powder of bigger size under argon gas sintering. The present work not only successfully solves these issues by decreasing the particle size and reducing the heating rate but also produces highly dense pellets with more than 98% density at 800 °C. We have also achieved a high conductivity of 8.77 × 10–4 S cm–1 at room temperature for the pellet sintered at just 800 °C in argon, which is 3–4 times higher than the conductivity of samples sintered at higher than 800 °C. Therefore, we succeeded in obtaining for the first time a high conductivity, pure phase, and high density of the LATP solid electrolyte at a relatively low temperature of 800 °C in an argon atmosphere, which is an important solution for solid-state battery fabrication by cosintering process. Furthermore, the stabilized NASICON electrolyte in an argon atmosphere also shows superior electrochemical performance when tested with Li metal in a symmetric battery cell.

MgF2 as an effective additive for improving ionic conductivity of ceramic solid electrolytes

As typical solid-state electrolytes (SSEs), Na1+xZr2SixP3−xO12 NASICONs provide an ideal platform for solid-state batteries (SSBs) that display higher safety and accommodate higher energy densities. The critical points for achieving SSBs with higher efficiencies are to improve essentially the ionic conductivity and to reduce largely the interfacial resistance between SSEs and cathode materials, which would necessitate extremely high level of craftsmanship and high-pressure equipment. An alternative to higher-performance and lower-cost SSBs is additive manufacturing. Here, we report on an effective additive, MgF2, which was used in synthesizing NASICONs, resulting in SSEs with fewer defects and higher performance. With an addition of mere 1 wt% MgF2 additive, the total room-temperature ionic conductivity of the NASICON electrolyte reaches up to 2.03 mS cm−1, improved up to ∼ 181.3%, with an activation energy of 0.277 eV. Meanwhile, the stability of the Na plating/stripping behavior in symmetric cells increases from 236 to 654 h. We tried to reveal the microscopic origins of the higher ionic conductivity of MgF2-doped NASICONs by comprehensive in-house characterizations. Our study discovers a novel MgF2 additive and provides an efficient way to prepare higher-performance SSEs, making it possible to fabricate lower-cost SSBs in industries.

Engineering the NASICON electrolyte/Na anode interface with amorphous bismuth oxide for sodium batteries.

Amorphous BiOx, prepared on the surface of NASICON electrolyte by the photochemical metal-organic deposition method, can substantially improve the interfacial properties at the anode side. The Na symmetric cell delivers a critical current density of 1.2 mA cm-2 and cycles stably at 0.5 mA cm-2 for 1000 h at 30 °C.

Artificial porous heterogeneous interface for all-solid-state sodium ion battery

Solid sodium-ion batteries are regarded as promising candidates for next-generation energy storage systems with high energy density and good safety. However, the large interface resistance and dendrite growth between sodium and solid electrolytes, especially at high current densities, severely limits their development. Herein, an artificial porous heterogeneous interface is constructed between sodium and the NASICON electrolyte Na3Hf2Si2PO12 (NHSP). This indicated that the porous heterogeneous interface with high-efficiency ion–electron transfer properties could effectively reduce the interface resistance, inhibit dendrites, and realize good rate performance. The symmetric cell with porous heterogeneous interface could cycle stably for more than 2000 h at 0.2 mA cm−2 at room temperature, and the critical current density reached 2.7 mA cm−2. Our study provides a promising direction for creating a stable interface that meets both the long-cycle and high-rate requirements for all-solid-state sodium-ion batteries.

Sc-doping in Na3Zr2Si2PO12 electrolytes enables preeminent performance of solid-state sodium batteries in a wide temperature range

Solid-state sodium batteries (SSSBs) display great potential in scale energy storage for their safety, cost and sustainability. However, it is a great challenge to achieve high ionic conductivity and temperature adaptability for most sodium-ion solid electrolytes. Here, we first demonstrate that Sc3+-doped Na3Zr2Si2PO12 (NASICON) is a promising electrolyte for a wide temperature range utilizing in SSSBs from 0 to 80 °C. Optimal Na3.4Zr1.6Sc0.4Si2PO12 shows a superior Na-ion conductivity, up to 1.77 × 10−3 S cm−1 at room temperature, and excellent Na metal compatibility, as confirmed by a symmetrical cell test. Furthermore, the solid-state sodium battery with the configuration of Na3V2(PO4)3/Na3.4Zr1.6Sc0.4Si2PO12/Na maintains a discharge capacity of 98.7 mAh g−1 at 1C after 300 cycles at room temperature. Even at 0 °C, the battery still displays a reversible capacity of 99.2 mAh g−1 at 0.1C after 100 cycles. Through the structure analysis and ex-situ and in-situ electrochemical characterizations, the reasons that dominate the excellent performance of the assembled all-solid-state sodium battery with NASICON electrolytes are initially revealed.

NMR Study of Lithium Transport in Liquid-Ceramic Hybrid Solid Composite Electrolytes.

Despite their high conductivity, factors such as being fragile enough to face processing issues and interfacial incompatibility with lithium electrodes are some of the main drawbacks hindering the commercialization of inorganic (mainly oxide-based) solid electrolytes for use in all-solid-state lithium batteries. To this end, strategies such as the addition of solid polymer electrolytes have been proposed to improve the electrode-electrolyte interface. Hybrid electrolytes, which are usually composed of ceramic particles dispersed in a polymer, generally have a better affinity with electrodes and higher ionic conductivity than pure inorganic electrolytes. However, a significant downside of this strategy is that differences in lithium transportability between electrolyte layers can result in the formation of a high interfacial energy barrier across the cell. One strategy to ensure sufficient "wetting" of ceramics is to incorporate a liquid electrolyte directly into the solid inorganic electrolyte resulting in the formation of a hybrid liquid-ceramic electrolyte. To this end, liquid-ceramic hybrid electrolytes were prepared by adding LiG4TFSI, a solvate ionic liquid (SIL), to garnet, NASICON, and perovskite-type ceramic electrolytes. Although SIL addition resulted in increased ionic conductivity, comparisons between the pure SIL and the hybrid systems revealed that improvements were due to the SIL alone. A thorough investigation of the hybrid systems by solid-state nuclear magnetic resonance (NMR) revealed little to no lithium exchange between the ceramic and the SIL. This confirms that lithium conductivity preferentially occurs through the SIL in these hybrid systems. The primary role of the ceramic is to provide mechanical strength.

Enhancing the Dendrite Tolerance of NaSICON Electrolytes by Suppressing Edge Growth of Na Electrode along Ceramic Surface

AbstractSolid‐state sodium batteries (SSNBs) have attracted extensive interest due to their high safety on the cell level, abundant material resources, and low cost. One of the major challenges in the development of SSNBs is the suppression of sodium dendrites during electrochemical cycling. The solid electrolyte Na3.4Zr2Si2.4P0.6O12 (NZSP) exhibits one of the best dendrite tolerances of all reported solid electrolytes (SEs), while it also shows interesting dendrite growth along the surface of NZSP rather than through the ceramic. Operando investigations and in situ scanning electron microscopy microelectrode experiments are conducted to reveal the Na plating mechanism. By blocking the surface from atmosphere access with a sodium‐salt coating, surface‐dendrite formation is prevented. The dendrite tolerance of Na | NZSP | Na symmetric cells is then increased to a critical current density (CCD) of 14 mA cm−2 and galvanostatic cycling of 1 mA cm−2 and 1 mAh cm−2 (half cycle) is demonstrated for more than 1000 h. Even if the current density is increased to 3 mA cm−2 or 5 mA cm−2, symmetric cells can still be operated for 180 h or 12 h, respectively.

Fundamental investigations on the sodium-ion transport properties of mixed polyanion solid-state battery electrolytes

Lithium and sodium (Na) mixed polyanion solid electrolytes for all-solid-state batteries display some of the highest ionic conductivities reported to date. However, the effect of polyanion mixing on the ion-transport properties is still not fully understood. Here, we focus on Na1+xZr2SixP3−xO12 (0 ≤ x ≤ 3) NASICON electrolyte to elucidate the role of polyanion mixing on the Na-ion transport properties. Although NASICON is a widely investigated system, transport properties derived from experiments or theory vary by orders of magnitude. We use more than 2000 distinct ab initio-based kinetic Monte Carlo simulations to map the compositional space of NASICON over various time ranges, spatial resolutions and temperatures. Via electrochemical impedance spectroscopy measurements on samples with different sodium content, we find that the highest ionic conductivity (i.e., about 0.165 S cm–1 at 473 K) is experimentally achieved in Na3.4Zr2Si2.4P0.6O12, in line with simulations (i.e., about 0.170 S cm–1 at 473 K). The theoretical studies indicate that doped NASICON compounds (especially those with a silicon content x ≥ 2.4) can improve the Na-ion mobility compared to undoped NASICON compositions.

Insight into synergetic effect of bulk doping and boundary engineering on conductivity of NASICON electrolytes for solid-state Na batteries

Na superionic conductor-type Na1+xZr2SixP3-xO12 (0 ≤ x ≤ 3, NZSPO) is considered as one of the most promising solid electrolytes for solid-state sodium batteries, while its relatively low ionic conductivity of 10−4 S cm−1 requires improvement for application. In this study, a synergetic strategy is applied to improve the ionic conductivity of NZSPO, i.e., by combining bulk doping and grain-boundary engineering. Hf4+ is selected as the substitution for Zr4+ to stabilize the highly conducting rhombohedral phase. La2O3 is added as a sintering aid to promote the ion transport along the grain boundaries with Na3La(PO4)2 formed therein. The optimized Na3Zr1.8Hf0.2Si2PO12-Na3La(PO4)2 (NZHSPO-NLPO) ceramic electrolytes show a high relative density of 98.8% and the superior ionic conductivity of 1.66 × 10−3 S cm−1 at 30 °C. The Na symmetric batteries display the stable plating/stripping cycling over 500 h at 0.1 mA cm−2 and 0.05 mAh cm−2. With ionic liquid as a wetting agent at cathode sides and PEO as an intermediate layer at anode sides, the NZHSPO-NLPO-based Na batteries with Na3V2(PO4)3 cathodes exhibit the discharge capacity of 109.9 mAh g−1 and capacity retention of 92.7% at 0.1 and 30 °C for 50 cycles. It is proved that the simultaneous optimization of bulk and grain boundaries is powerful for increasing the ionic conductivity of ceramic solid electrolytes.