Cycling degradation and safety issues in sodium-ion batteries: Promises of electrolyte additives

Achieving the Inhibition of Aluminum Corrosion by Dual-Salt Electrolytes for Sodium-Ion Batteries

Sodium bis(fluorosulfonyl)imide (NaFSI) electrolytes are renowned for their superior physicochemical and electrochemical properties, making them ideal for high-performance sodium-ion batteries (SIBs). However, severe oxidative dissolution of aluminum current collectors (commonly known as Al corrosion) in NaFSI-based electrolytes occurs at high potentials. To address this challenge, aiming to understand the Al corrosion mechanism and develop strategies to inhibit corrosion, we propose dual-salt electrolytes using 0.8 mol L-1 (M) NaFSI and 0.2 M of a second fluorine-containing sodium salt dissolved in EC/PC solutions (1:1, v/v) to construct an insoluble deposits layer on the Al. Dual-salt electrolytes adopting a second sodium salt capable of passivating the Al collector have been extensively investigated through various techniques, such as cyclic voltammetry, scanning electron microscopy, chronoamperometry, X-ray photoelectron spectroscopy, and charge-discharge tests. Our findings demonstrate that introducing sodium difluoro(oxalato)borate (NaDFOB) into the NaFSI electrolytes inhibits Al corrosion, which is attributed to the formation of insoluble deposits of Al-F (AlF3) and B-F containing polymers. Moreover, the capacity retention of Na||Na3V2(PO4)3 (NVP) cells using the NaFSI-NaDFOB dual-salt electrolyte reaches 99.2% along with a Coulombic efficiency over 99.3% at a 1 C rate after 200 cycles. This research provides a practical solution for passivating Al collectors in SIBs with NaFSI electrolytes and promotes the development of sodium batteries with long calendar lifetimes.

Extended Battery Compatibility Consideration from an Electrolyte Perspective

The performance of electrochemical batteries is intricately tied to the physicochemical environments established by their employed electrolytes. Traditional battery designs utilizing a single electrolyte often impose identical anodic and cathodic redox conditions, limiting the ability to optimize redox environments for both anode and cathode materials. Consequently, advancements in electrolyte technologies are pivotal for addressing these challenges and fostering the development of next-generation high-performance electrochemical batteries. This review categorizes perspectives on electrolyte technology into three key areas: additives engineering, comprehensive component analysis encompassing solvents and solutes, and the effects of concentration. By summarizing significant studies, the efficacy of electrolyte engineering is highlighted, and the review advocates for further exploration of optimized component combinations. This review primarily focuses on liquid electrolyte technologies, briefly touching upon solid-state electrolytes due to the former greater vulnerability to electrode and electrolyte interfacial effects. The ultimate goal is to generate increased awareness within the battery community regarding the holistic improvement of battery components through optimized combinations.

A Sodium Bis(fluorosulfonyl)imide (NaFSI)-based Multifunctional Electrolyte Stabilizes the Performance of NaNi1/3Fe1/3Mn1/3O2/hard Carbon Sodium-ion Batteries

A sodium bis(fluorosulfonyl)imide (NaFSI)-based multifunctional electrolyte is developed by partially replacing NaPF6 salt in the electrolyte to improve the wide temperature range working capability of NaNi1/3Fe1/3Mn1/3O2/hard carbon (NNFM111/HC) sodium-ion batteries (SIBs). The capacity retention of the SIBs with NaFSI-NaPF6 dual salt electrolyte increases from 47.2 % to 75.5 % after 250 cycles at 25 °C, and from 51.0 % to 82.3 % after 80 cycles at 45 °C, and the 1 C discharge capacity retention at the low temperature of -20 °C also increases 26.8 %. In the single salt system, NaPF6 effectively passivate the aluminum foil and NaFSI passivate the electrode/electrolyte interface. The synergistic effect of NaPF6 and NaFSI greatly improves the battery performance in a wide temperature range. This NaFSI-based dual salt electrolyte also effectively overcomes the flaws when the SIBs using NaFSI or NaPF6 independently, and makes it more suitable for SIBs, indicating promising prospects in the commercial application of NNFM111/HC SIBs.

Electrolytes for Sodium Ion Batteries: The Current Transition from Liquid to Solid and Hybrid systems

Sodium-ion batteries (NIBs) have recently garnered significant interest in being employed alongside conventional lithium-ion batteries, particularly in applications where cost and sustainability are particularly relevant. The rapid progress in NIBs will undoubtedly expedite the commercialization process. In this regard, tailoring and designing electrolyte formulation is a top priority, as they profoundly influence the overall electrochemical performance and thermal, mechanical, and dimensional stability. Moreover, electrolytes play a critical role in determining the system's safety level and overall lifespan. This review delves into recent electrolyte advancements from liquid (organic and ionic liquid) to solid and quasi-solid electrolyte (dry, hybrid, and single ion conducting electrolyte) for NIBs, encompassing comprehensive strategies for electrolyte design across various materials, systems, and their functional applications. The objective is to offer strategic direction for the systematic production of safe electrolytes and to investigate the potential applications of these designs in real-world scenarios while thoroughly assessing the current obstacles and forthcoming prospects within this rapidly evolving field.

Enhanced Sodium Ion Batteries' Performance: Optimal Strategies on Electrolytes for Different Carbon-based Anodes

Carbon-based materials have emerged as promising anodes for sodium-ion batteries (SIBs) due to the merits of cost-effectiveness and renewability. However, the unsatisfactory performance has hindered the commercialization of SIBs. During the past decades, tremendous attention has been put into enhancing the electrochemical performance of carbon-based anodes from the perspective of improving the compatibility of electrolytes and electrodes. Hence, a systematic summary of strategies for optimizing electrolytes between hard carbon, graphite, and other structural carbon anodes of SIBs is provided. The formulations and properties of electrolytes with solvents, salts, and additives added are comprehensively presented, which are closely related to the formation of solid electrolyte interface (SEI) and crucial to the sodium ion storage performance. Cost analysis of commonly used electrolytes has been provided as well. This review is anticipated to provide guidance in future rational tailoring of electrolytes with carbon-based anodes for sodium-ion batteries.

Recent Advances in Sodium-Ion Batteries: Cathode Materials

Emerging energy storage systems have received significant attention along with the development of renewable energy, thereby creating a green energy platform for humans. Lithium-ion batteries (LIBs) are commonly used, such as in smartphones, tablets, earphones, and electric vehicles. However, lithium has certain limitations including safety, cost-effectiveness, and environmental issues. Sodium is believed to be an ideal replacement for lithium owing to its infinite abundance, safety, low cost, environmental friendliness, and energy storage behavior similar to that of lithium. Inhered in the achievement in the development of LIBs, sodium-ion batteries (SIBs) have rapidly evolved to be commercialized. Among the cathode, anode, and electrolyte, the cathode remains a significant challenge for achieving a stable, high-rate, and high-capacity device. In this review, recent advances in the development and optimization of cathode materials, including inorganic, organometallic, and organic materials, are discussed for SIBs. In addition, the challenges and strategies for enhancing the stability and performance of SIBs are highlighted.

Electrochemical Response of 3D-Printed Free-Standing Reduced Graphene Oxide Electrode for Sodium Ion Batteries Using a Three-Electrode Glass Cell

Graphene and its derivatives have been widely used to develop novel materials with applications in energy storage. Among them, reduced graphene oxide has shown great potential for more efficient storage of Na ions and is a current target in the design of electrodes for environmentally friendly Na ion batteries. The search for more sustainable and versatile manufacturing processes also motivates research into additive manufacturing electrodes. Here, the electrochemical responses of porous 3D-printed free-standing log-type structures fabricated using direct ink writing (DIW) with a graphene oxide (GO) gel ink are investigated after thermal reduction in a three-electrode cell configuration. The structures delivered capacities in the range of 50-80 mAh g-1 and showed high stability for more than 100 cycles. The reaction with the electrolyte/solvent system, which caused an initial capacity drop, was evidenced by the nucleation of various Na carbonates and Na2O. The incorporation of Na into the filaments of the structure was verified with transmission electron microscopy and Raman spectroscopy. This work is a proof of concept that structured reduced GO electrodes for Na ion batteries can be achieved from a simple, aqueous GO ink through DIW and that there is scope for improving their performance and capacity.