Electrolyte Design Strategies for Aqueous Sodium-Ion Batteries: Progress and Prospects.

Sodium-ion batteries (SIBs) have emerged as one of today's most attractive battery technologies due to the scarcity of lithium resources. Aqueous sodium-ion batteries (ASIBs) have been extensively researched for their security, cost-effectiveness, and eco-friendly properties. However, aqueous electrolytes are extremely limited in practical applications because of the narrow electrochemical stability window (ESW) with extremely poor low-temperature performance. The first part of this review is an in-depth discussion of the reasons for the inferior performance of aqueous electrolytes. Next, research progress in extending the electrochemical stabilization window and improving low-temperature performance using various methods such as "water-in-salt", eutectic, and additive-modified electrolytes is highlighted. Considering the shortcomings of existing solid electrolyte interphase (SEI) theory, recent research progress on the solvation behavior of electrolytes is summarized based on the solvation theory, which elucidates the correlation between the solvation structure and the electrochemical performance, and three methods to upgrade the electrochemical performance by modulating the solvation behavior are introduced in detail. Finally, common design ideas for high-temperature resistant aqueous electrolytes that are hoped to help future aqueous batteries with wide temperature ranges are summarized.

A High-Voltage Cathode Material with Ultralong Cycle Performance for Sodium-Ion Batteries.

Vanadium-based polyanionic materials are promising electrode materials for sodium-ion batteries (SIBs) due to their outstanding advantages such as high voltage, acceptable specific capacity, excellent structural reversibility, good thermal stability, etc. Polyanionic compounds, moreover, can exhibit excellent multiplicity performance as well as good cycling stability after well-designed carbon covering and bulk-phase doping and thus have attracted the attention of multiple researchers in recent years. In this paper, after the modification of carbon capping and bulk-phase nitrogen doping, compared to pristine Na3V2(PO4)3, the well optimized Na3V(PO3)3N/C possesses improved electromagnetic induction strength and structural stability, therefore exhibits exceptional cycling capability of 96.11% after 500 cycles at 2 C (1 C = 80 mA g-1) with an elevated voltage platform of 4 V (vs Na+/Na). Meanwhile, the designed Na3V(PO3)3N/C possesses an exceptionally low volume change of ≈0.12% during cycling, demonstrating its quasi-zero strain property, ensuring an impressive capacity retention of 70.26% after 10,000 cycles at 2 C. This work provides a facial and cost-effective synthesis method to obtain stable vanadium-based phosphate materials and highlights the enhanced electrochemical properties through the strategy of carbon rapping and bulk-phase nitrogen doping.

Recent advances on low-Co and Co-free high entropy layered oxide cathodes for lithium-ion batteries.

As the price of the precious metal cobalt continues to rise, there is an urgent need for a cobalt-free or low-cobalt electrode material to reduce the cost of lithium-ion batteries, which are widely used commercially, while maintaining their performance as much as possible. With the introduction of the new concept of high entropy (HE) materials into the battery field, low cobalt and cobalt free HE novel lithium-ion batteries have attracted great attention. It possesses important research value to use HE materials to reduce the use of cobalt metal in electrode materials. In this perspective, the comparison between the new cathode materials of low cobalt and cobalt-free HE lithium-ion battery and traditional cathode materials and the latest progress in maintaining structural stability and conductivity are introduced. It is believed that low cobalt and cobalt-free and HE layered oxides can be used to replace the function of cobalt in the cathode materials of lithium-ion batteries. Finally, the future research directions and the synthesis method of HE cathode materials for lithium-ion batteries are also discussed.

Reactive boride as a multifunctional interface stabilizer for garnet-type solid electrolyte in all-solid-state lithium batteries.

All-solid-state batteries are one of the most important game changers in electrochemical energy storage since they are free from the risk of leakage of hazardous flammable liquid solvents. Among the various types of solid-state electrolytes, Li7-xLa3Zr2-xTaxO12 garnets possess many desirable advantages to be considered a suitable candidate for lithium-ion batteries. However, their practical application has been hindered by premature short-circuits due to lithium dendrite growth, nonnegligible electronic conductivity and interfacial air sensitivity issues. Herein, we propose a multifunctional layer strategy to simultaneously address both the interface and electronic conductivity issues. With the help of a facile chemical process based on reactive cobalt boride, electron leakage was effectively blocked and the electrochemical performance/stability could be well maintained over extended cycles. The cobalt boride-coating layer also possessed an impressive Li metal wetting ability while sustaining a low interfacial resistance. A full cell paired with a commercialized cathode showed satisfactory performance with low overpotentials and a high specific capacity over 150 mA h g-1. Moreover, first-principle calculations further revealed the status of the rearrangement of the electron cloud behind the charge-density difference, and the nature of the low diffusion energy barrier of the reactive cobalt boride protective layer. Our strategy highlights the necessity of designing proper multifunctional layers in the garnet-type solid-state lithium-ion battery system.