Mg 2+ /F − Synergy to Enhance the Ionic Conductivity of Na 3 Zr 2 Si 2 PO 12 Solid Electrolyte for Solid‐State Sodium Batteries

Pristine NASICON Electrolyte: A High Ionic Conductivity and Enhanced Dendrite Resistance Through Zirconia (ZrO2) Impurity-free Solid-Electrolyte Design

Sodium batteries are considered a promising candidate for large-scale grid storage at tropical climate zone, and solid-state sodium metal batteries have a strong proposition as high energy density battery. The main challenge is to develop ultra-pure solid-state ceramic electrolyte and compatible metal interface. Here, a scalable and energy-efficient synthesis strategy of sodium (Na) Super Ionic CONductor, Na1+xZr2SixP3-xO12 (x = 2, NZSP) solid electrolyte, has been introduced with the complete removal of unreacted zirconium oxide (ZrO2) impurities. Additionally, the reaction mechanism for the formation of pure phase NZSP is reported for the first time. The NZSP prepared by utilizing the Zr precursor, i.e., tetragonal zirconium oxide (t-ZrO2) derived from the Zr(OH)4 gets quickly and completely consumed in the synthesis process leaving no unreacted monoclinic ZrO2 impurities. The synthesis process only needs a minimum stay of 4 h, which is three times less than the conventional synthesis method. The elimination of ZrO2 impurities results in a 2.5-fold reduction in grain boundary resistivity, showcasing a total ionic conductivity of 1.75 mS cm-1 at room temperature and a relative density of 98%. The prepared electrolyte demonstrates remarkable resistance to dendrite formation, as evidenced by a high critical current density value of 1.4 mA cm-2.

Overview of Inorganic Electrolytes for All-Solid-State Sodium Batteries

All-solid-state sodium batteries (AS3B) emerged as a strong contender in the global electrochemical energy storage market as a replacement for current lithium-ion batteries (LIB) owing to their high abundance, low cost, high safety, high energy density, and long calendar life. Inorganic electrolytes (IEs) are highly preferred over the conventional liquid and solid polymer electrolytes for sodium-ion batteries (SIBs) due to their high ionic conductivity (∼10-2-10-4 S cm-1), wide potential window (∼5 V), and overall better battery performances. This review discusses the bird's eye view of the recent progress in inorganic electrolytes such as Na-β"-alumina, NASICON, sulfides, antipervoskites, borohydride-type electrolytes, etc. for AS3Bs. Current state-of-the-art inorganic electrolytes in correlation with their ionic conduction mechanism present challenges and interfacial characteristics that have been critically reviewed in this review. The current challenges associated with the present battery configuration are overlooked, and also the chemical and electrochemical stabilities are emphasized. The substantial solution based on ongoing electrolyte development and promising modification strategies are also suggested.

Preparation of Zn3Nb2O8 anode material for high-performance lithium/sodium-ion batteries

Niobium-based oxides (M-Nb-O) as promising lithium/sodium-ion storage anode materials have attracted much attention. More types of niobium-based oxides are prepared in order to provide more candidates for anode materials. Herein, Zn3Nb2O8 as a novel intercalation-type anode material has been reported for the first time. Arborescent Zn3Nb2O8 particles (Zn3Nb2O8-A) and stump-like Zn3Nb2O8 particles (Zn3Nb2O8-B) have been prepared by solid-state and solvothermal methods, respectively. Benefiting from the microsized stump-like structure and the exposure of the (110) facet, Zn3Nb2O8-B delivers superior long-term cycling stability with a 139.6% capacity retention (291.8 mA h g-1) over 650 cycles at 0.5 A g-1 and a large reversible specific capacity of 91.4 mA h g-1 at 4.0 A g-1 in lithium-ion batteries. Furthermore, the Zn3Nb2O8-B electrode exhibits outstanding cycling stability (100.1 mA h g-1 with 94.5% capacity retention after 400 cycles at 0.5 A g-1) in sodium-ion batteries. The excellent electrochemical performance of the stump-like Zn3Nb2O8-B materials can be attributed to the exposure of the (110) facet, enlarged interlayer spacing, small charge transfer resistance, and high pseudocapacitive contribution. Therefore, Zn3Nb2O8-B has great application prospects as an anode material for lithium/sodium-ion storage.

Sandwiched composite electrolyte with excellent interfacial contact for high-performance solid-state sodium-ion batteries

Solid-state sodium-ion batteries have attracted significant attention due to their rich resources, high safety, and high energy density. However, the lower ionic conductivity and inferior interfacial contact between solid-state electrolytes (SSEs) and electrodes limit their practical applications. Herein, polyvinylideneuoride-co-hexauoropropylene (PVDF-HFP) membrane is selected and a novel sandwiched composite PVDF-HFP/Na2.5Zr1.95Ce0.05Si2.2P0.8O11.3F0.7/PVDF-HFP (G-NZC0.05SPF0.7-G) SSEs is well designed. The ionic conductivity of Na3Zr2Si2PO12 is enhanced by Ce4+/F- co-doping. The effects of Ce4+ and F- doping on the crystal structure, density, and ionic conductivity for Na3Zr2Si2PO12 are well investigated. The optimal NZC0.05SPF0.7 delivers a high ionic conductivity of 1.39 × 10-3 S cm-1 at 25 ℃. Moreover, the PVDF-HFP membrane can significantly enhance the interface compatibility between NZC0.05SPF0.7 and electrodes. The as-prepared G-NZC0.05SPF0.7-G exhibits a large ionic conductivity of 1.07 × 10-3 S cm-1 at 25 ℃, wide electrochemical stability window up to 4.5 V, high critical current density of 1.2 A cm-2, and stable Na plating/stripping over 600 h at 0.3 A cm-2. The solid-state Na0.67Mn0.47Ni0.33Ti0.2O2/G-NZC0.05SPF0.7-G/Na battery delivers a remarkable cycling stability and rate capability at 25 ℃, indicating that the as-prepared G-NZC0.05SPF0.7-G has a promising application for solid-state SIBs. This study demonstrates an effective strategy to develop advanced solid-state electrolytes for solid-state SIBs.

Active Control of Interface Dynamics in NASICON-Based Rechargeable Solid-State Sodium Batteries

Severe challenges are restraining the practical application of solid-state batteries, such as the dendrite growth and unsatisfactory compatibility between solid electrolyte and electrode. Here, we propose an interface dynamic control (IDC) strategy to ensure the stable operation of NASICON-based solid-state sodium batteries. First, we introduce intergranular phase (CuO) to effectively promote the densification of Na₃Zr₂Si₂PO₁₂ with an optimized ionic conductivity of 1.74 × 10^-3 S cm^-1 at 25 °C. Moreover, the kinetically formed Na-Cu-O interlayer reveals outstanding conductive capability. The dramatically reduced interfacial area-specific resistance (70 ohm cm^-2) boosts the resistance to Na dendrite growth, ensuring the excellent cycling stability of symmetric Na cells at a current density of 0.4 mA cm^-2 and room temperature. All-solid-state sodium metal batteries with Na₃V_1.5Cr_0.5(PO₄)₃ cathode and modified Na₃Zr₂Si₂PO₁₂ ceramic electrolyte reveal a high retention of 87.4% at 100 mA g^-1 over 300 cycles. This work opens up a new route for the rational interface design of NASICON-structure solid electrolyte toward the application in the high energy-density and high safety electrochemical energy storage devices.