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.

Fluorine Rich Borate Salt Anion Based Electrolyte for High Voltage Sodium Metal Battery Development.

This study demonstrates the enhanced performance in high-voltage sodium full cells using a novel electrolyte composition featuring a highly fluorinated borate ester anion (1 M Na[B(hfip)4].3DME) in a binary carbonate mixture (EC:EMC), compared to a conventional electrolyte (1 M Na[PF6] EC:EMC). The prolonged cycling performance of sodium metal battery employing high voltage cathodes (NVPF@C@CNT and NFMO) is attributed to uniform and dense sodium deposition along with the formation of fluorine and boron-rich solid electrolyte interphase (SEI) on the sodium metal anode. Simultaneously, a robust cathode electrolyte interphase (CEI) is formed on the cathode side due to the improved electrochemical stability window and superior aluminum passivation of the novel electrolyte. The CEIs on high-voltage cathodes are discovered to be abundant in C-F, B-O, and B-F components, which contributes to long-term cycling stability by effectively suppressing undesirable side reactions and mitigating electrolyte decomposition. The participation of DME in the primary solvation shell coupled with the comparatively weaker interaction between Na+ and [B(hfip)4]- in the secondary solvation shell, provides additional confirmation of labile desolvation. This, in turn, supports the active participation of the anion in the formation of fluorine and boron-rich interphases on both the anode and cathode.

Lower Diffusion-Induced Stress in Nano-Crystallites of P2-Na2/3 Ni1/3 Mn1/2 Ti1/6 O2 Novel Cathode for High Energy Na-ion Batteries.

P2-type Na2/3 Ni1/3 Mn1/2 Ti1/6 O2 (NMTNO) cathode is a preeminent electrode material for Na-ion batteries owing to its open prismatic framework, air-moisture stability, inexpensiveness, appealing capacity, environmental benignity, and Co-free composition. However, the poor cycling stability, sluggish Na-ion kinetics induced in bulk-sized cathode particles, cracking, and exfoliation in the crystallites remain a setback. To outmaneuver these, a designing strategy of a mechanically robust, hexagonal nano-crystallites of P2-type Na2/3 Ni1/3 Mn1/2 Ti1/6 O2 (NMTNOnano ) electrode via quick, energy-efficient, and low-cost microwave-irradiated synthesis is proposed. For the first time, employing a unified experimental and theoretical approach with fracture mechanics analysis, the mechanism behind the enhanced performance, better structural stability, and lower diffusion-induced stress of NMTNOnano compared to micro-sized Na2/3 Ni1/3 Mn1/2 Ti1/6 O2 is unveiled and the electrochemical shock map is predicted. The NMTNOnano cathode provides 94.8% capacity retention after 100 cycles at 0.1 C with prolonged performance for 1000 cycles at 0.5 C. The practical viability of this cathode, tested in a full cell against a hard carbon anode delivered 85.48% capacity retention at 0.14 mA cm-2 after 200 cycles. This work bridges the gap in correlating the microstructural and electrochemical properties through experimental, theoretical (DFT), and fracture mechanics analysis, thereby tailoring efficient cathode with lower diffusion-induced stress for high-energy Na-ion batteries.

Artificial Organo-Fluoro-Rich Anode Electrolyte Interface and Partially Sodiated Hard Carbon Anode for Improved Cycle Life and Practical Sodium-Ion Batteries.

In this work, a strategy is introduced wherein without keeping any excess cathode, a practical full-cell sodium-ion battery has been demonstrated by utilizing a hard carbon (HC) anode and sodium vanadium fluorophosphate and carbon nanotube composite (NVPF@C@CNT) cathode. A thin, robust, and durable solid electrolyte interface (SEI) is created on the surface of HC through its incubation wetted with a fluoroethylene carbonate (FEC)-rich warm electrolyte in direct contact with Na metal. During the incubation, the HC anode is partially sodiated and passivated with a thin SEI layer. The sodium-ion full cell fabricated while maintaining N/P ∼1.1 showed the first cycle Coulombic efficiency of ∼97% and delivered a stable areal capacity of 1.4 mAh cm-2 at a current rate of 0.1 mA cm-2 realized for the first time to the best of our knowledge. The full cell also showed a good rate capability, retaining 1.18 mAh cm-2 of its initial capacity even at a high current rate of 0.5 mA cm-2, and excellent cycling stability, giving a capacity of ∼1.0 mAh cm-2 after 500 cycles. The current strategy presents a practical way to make a sodium-ion full cell, utilizing no excess cathode material, significantly saving cost and time.

Direct-Contact Prelithiation of Si-C Anode Study as a Function of Time, Pressure, Temperature, and the Cell Ideal Time.

Direct-contact prelithiation (PL) is a facile, practical, and scalable method to overcome the first-cycle loss and large volume expansion issues for silicon anode (with 30 wt % Si loading) material, and a detailed study is absent. Here, an understanding of direct-contact PL as a function of the PL time, and the effects of externally applied pressure (weight), microstructure, and operating temperature have been studied. The impact of PL on the Si-C electrode surfaces has been analyzed by electrochemical techniques and different microstructural analyses. The solid electrolyte interface (SEI) layer thickness increases with the increase in PL time and decreases after 2 min of PL time. The ideal PL time was found to be between 15 (PL-15) and 30 (PL-30) min with 83.5 and 97.3% initial Coulombic efficiency (ICE), respectively, for 20 g of externally applied weight. The PL-15 and PL-30 cells showed better cyclic stability than PL-0 (without prelithiation), with more than 90% capacity retention after 500 cycles at 1 A g-1 current density. The discharge capacities for PL-15 and PL-30 have been observed as highest at 45 °C operating temperature with limited cyclability. We propose here a synchronization strategy in prelithiation time, pressure, and temperature to achieve excellent cell performance.

Development of high-voltage pulse generator with variable amplitude and duration.

A high voltage pulse generator with variable amplitude (100-3000 V) and duration (100-2000 µs) has been designed and developed. The variable duration pulse has been generated by adopting a simple and novel technique of varying the turn off delay time of a high voltage Metal Oxide Semiconductor Field Effect Transistor (MOSFET) based switch by varying external gate resistance. The pulse amplitude is made variable by adjusting biasing supply of the high voltage switch. The high voltage switch has been developed using a MOSFET based stack of 3 kV rating with switching time of 7 ns.