Due to the abundance of sodium resources and low cost, sodium-based solid-state batteries have great potential in the next generation of batteries. However, in the development of room-temperature solid-state sodium batteries, it has been a challenge to fabricate thin, self-contained solid electrolytes that can cycle sodium at high current densities.
Eric Wachsman's team at the University of Maryland in the United States achieved 3Very low anode interface resistance of 5 cm2. As a result, the critical current density reached a record 30 mA cm2 and the sodium cycle cumulative capacity reached 108 ah/cm2。In addition, as a proof of concept, pouch cells were assembled with a Na3V2(PO4)3 cathode and a sodium metal anode on a dense and porous electric double-layer electrolyte, and cycle rates of up to 2C were achieved at room temperature without tandem pressure. The results were published in Energy & Environmental Science under the title "High-rate cycling in 3D dual-doped nasicon architectures toward room-temperature sodium-metal-anode solid-state batteries". First Author: Prem Jaschin.
[Introduction].
Sodium-ion batteries based on sodium metal anodes have a low redox potential (271 v vs.SHE) and high theoretical capacity (1165 mAg), sodium salts are ubiquitous, providing a more potential low-cost alternative to meet the rapidly growing demand for energy storage. With the discovery of a new high-pressure sodium intercalated cathode with high specific capacity, sodium-ion batteries will soon be able to match the energy density benchmark set by lithium-ion batteries. However, conventional sodium-ion batteries containing a liquid electrolyte have an inherent risk of volatility and flammability, while solid-state batteries offer a safer and more stable alternative. Among several sodium-ion conductive inorganic solid electrolytes, the Nasicon series of compounds with the general formula Na1+XZR2SIXP3-XO12 (0 x 3) has good ionic conductivity (067 ms cm), air stability, compositional adjustability, and mechanical strength. 6 9 The abundance of sodium (23,600 ppm), zirconium (132 ppm), silicon (282,000 ppm) and phosphorus (567 ppm) in the earth's crust makes it possible to produce low-risk NASICON at a lower cost on a global scale, enabling critical grid-scale storage.
The fundamental challenges for solid-state sodium batteries (SSSBs) to achieve high energy density (200 Wh kg) include obtaining a stable interface between the sodium metal anode and the NASICON solid electrolyte (SE), as well as fabricating a thin (about 10 m) dense SE. The sodium-SE interface suffers from high interfacial contact resistance, void formation during cycling, dendrite dendrite propagation (and therefore low critical current density (CCD)), and interfacial electrochemical instability. Annealing, alloys (including sn-na, Na-SiO2 composite anodes), surface coatings, and duplex composites (Na2B4O7-Nasicon composites) are all ways to improve interfacial resistance and CCD. However, the CCD obtained is still only 06–2.5 mA cm2. To date, using a NASICON-based electrolyte, combined with a stacking pressure (6 12 MPa) and a nano3 protective layer that inhibits surface dendrites, the highest CCD obtained is 14 mA cm2 (MA et al.). To the best of the investigators' knowledge, long-term stable sodium cycling at room temperature remains to be achieved at current densities greater than 1 mA cm2 and no superimposed pressures.
[Key points of work].
In this study, the authors demonstrate fabrication methods for porous-dense porous three-layer and porous-dense bilayer three-dimensional NASICON structures. These designs increase SSSB energy density (by reducing SE thickness) and minimize anode-electrolyte interface resistance (increased sodium-Nasicon surface contact area compared to planar geometry). The porous layer improves mechanical strength and acts as a three-dimensional network matrix for the electrode material, ensuring seamless contact between the cells during cycling. A thin dense layer acts as an insulating barrier and prevents the diffusion of active electrode components.
The poor wettability of NASICON and sodium and the instability with molten sodium pose a challenge to penetrate into the pores of the bilayer and trilayer structure. To date, the only reported structure of porous Nasicon is an attempt by Lu et al. on particles about 500 m thick. While the pores in the three layers (chemically modified with SNO2) successfully infiltrate sodium, the circulating current of sodium is only 03 ma/cm2。However, for the first time, atomic layer deposition (ALD) was used to modify the conformal coating of nanoscale zinc oxide on the surface of NASICON, thereby improving the sodium wettability of the entire three-dimensional SE framework. The zinc oxide coating also acts as a protective layer to prevent further chemical reduction of NASICON when it comes into contact with molten sodium at high temperatures.
In this paper, the researchers addressed these challenges by: (i) developing a more conductive NASICON component;(ii) modify the NASICON surface so that it can wet sodium with a stable low interfacial impedance;(iii) the fabrication of a porous dense three-layer structure using a thin (approximately 25 m) dense Nasicon layer to achieve a high-magnification sodium cycle;and (iv) a high-rate all-cell demonstrated using a porous, dense electric double-layer electrolyte design.
Optimized the composition of the NASICON
Figure 1(a) na365zr1.675zn0.2mg0.X-ray diffraction pattern of 125Si2PO12. (b) Monoclinic unit lattice parameters and (c) Orthorhombic lattice-monoclinic lattice phase fraction as a function of dopant. (d) Plot of ionic conductivity versus dopant. (e) na3.65zr1.675zn0.2mg0.Arrhenius diagram of ionic conductivity as a function of temperature and (f) critical current density plot (symmetric unit cell) of 125Si2PO12.
Figure 2 (a) Cross-sectional scanning electron microscopy of a double-doped Nasicon three-layer structure after sintering (b) porous layer, (c) dense layer, and (d) top surface image (the inset in (a) shows an optical image of the three-layer structure). Cross-section of sodium infiltration into the double-doped Nasicon trilayer structure (e) secondary electron image and (f) backscattered electron image (magnified region) (the markings in (f) illustrate the sodium-filled region).
Porous-dense-porous three-layer NASICON structure
Figure 3 (a) Schematic diagram of a symmetrical cell module based on a three-layer membrane (inset shows the magnified area of (a) depicting the flow of sodium ions during the peeling process). (b) and (c) show the exfoliation and deposition mechanism of sodium metal through three layers of pores under the action of an impressed current.
Figure 4(a) Potential response of a zinc- and magnesium-doped NASICON three-layer symmetrical cell to CCD test at room temperature and without stack pressure. Step size 0625 mA cm2 is between 0625 to 25 mA cm2, 25 mA cm2 is between 25 to 42Room temperature electrical constant current cycles of (b) sodium-symmetrical cells between 5 mA cm2 with current densities of and 30 mA cm2, measured for 1 h per cycle. Enlarged plots of sodium cycle voltage curves recorded at (C) 15 mA cm2 and (D) 30 mA cm2. (e) Change in area-specific resistance of a symmetrical cell during electrical constant current cycling at and 30 mA cm2.
Figure 5 depicts the passage of room-temperature sodium cycles through various inorganic ceramic solid electrolytes published in the literature.
Figure 6 (a) Optical image of a Nasicon bilayer doped with zinc-magnesium and (b) cross-sectional scanning electron microscope image. (c) Schematic diagram of the pouch cell and **,d) charge-discharge curves, (e) cycle performance (at 0.).2C), as well as (F) rate capability test of NVP Zn, Mg-doped Nasicon NA settings measured at room temperature.
[Conclusion].
Na3Zr2SiPO12 doped with Zn2+- and Mg2+ was successfully synthesized by solid-state synthesis. This dual-doping method achieves a high orthorhombic phase fraction (46%) and a larger sodium conduction channel, resulting in improved ionic conductivity across grains and grain boundaries of 63 ms cm and 44 ms/cm。The total ionic conductivity of the double-doped NASICON system was determined to be 27 ms cm, with the associated migration barrier as low as 029 EV while the migration barrier and migration barrier of undoped NASICON were 025 ms cm and 036 ev。Using this NASICON component, a three-layer porous, dense structure was successfully fabricated using a scalable ribbon casting process. A thin dense layer of 25 m with a thickness of 50 to 60 m and a porous layer with a pore size of about 10 m were obtained. By applying an ALD coating of zinc oxide to the NASICON surface, the wettability is significantly improved. The pores are efficiently filled with sodium metal, establishing a continuous interfacial contact with an interface resistance as low as 35 cm2, which is much lower than the planar geometry (9 cm2). A symmetrical battery using three layers of NASICON electrolyte exhibited a stable voltage lag at a current density of and 15 mA cm2 during corona quiescent sodium cycling for a total time of 620 hours. After a further 146 hours of sodium cycling at 30 mA cm2, a short circuit occurred, with a cumulative volume of 542 ah/cm2。A flat, porous, dense, double-layer structure using a double-doped NASICON electrolyte provides a preliminary demonstration of an all-sodium battery. Pouch cells assembled using Nasicon electric double layer doped with Zn, Mg, have a metal sodium anode and Na3V2(PO4)3 cathode at 0The capacitance at 2 C is 116 mAh g, and after 300 cycles, the capacitance is still 66% of the initial capacitance. The successful stabilization of sodium cycling at high current densities and the complete cycling of batteries using a thin, three-dimensional ionic conductive NASICON solid electrolyte is a significant advance in this critical sustainable energy storage technology.