Deciphering Electrolyte Dominated Na+ Storage Mechanisms in Hard Carbon Anodes for Sodium-Ion Batteries

Challenges and Breakthroughs in Enhancing Temperature Tolerance of Sodium-Ion Batteries

Lithium-based batteries (LBBs) have been highly researched and recognized as a mature electrochemical energy storage (EES) system in recent years. However, their stability and effectiveness are primarily confined to room temperature conditions. At temperatures significantly below 0 °C or above 60 °C, LBBs experience substantial performance degradation. Under such challenging extreme contexts, sodium-ion batteries (SIBs) emerge as a promising complementary technology, distinguished by their fast dynamics at low-temperature regions and superior safety under elevated temperatures. Notably, developing SIBs suitable for wide-temperature usage still presents significant challenges, particularly for specific applications such as electric vehicles, renewable energy storage, and deep-space/polar explorations, which requires a thorough understanding of how SIBs perform under different temperature conditions. By reviewing the development of wide-temperature SIBs, the influence of temperature on the parameters related to battery performance, such as reaction constant, charge transfer resistance, etc., is systematically and comprehensively analyzed. The review emphasizes challenges encountered by SIBs in both low and high temperatures while exploring recent advancements in SIB materials, specifically focusing on strategies to enhance battery performance across diverse temperature ranges. Overall, insights gained from these studies will drive the development of SIBs that can handle the challenges posed by diverse and harsh climates.

Hard Carbon Derived From Different Precursors for Sodium Storage

Due to the almost unlimited resource and acceptable performance, Sodium-ion batteries (SIBs) have been regarded as a promising alternative for lithium-ion batteries (LIBs) for grid-scale energy storage. As the key material of SIBs, hard carbon (HC) plays a decisive role in determining the batteries' performance. Nevertheless, the micro-structure of HCs is quite complex and the random organization of turbostratically stacked graphene layers, closed pores, and defects make the structure-performance relationship insufficiently revealed. On the other hand, the impending large-scale deployment of SIBs leads to producing HCs with low-cost and abundant precursors actively pursued. In this work, the recent progress of preparing HCs from different precursors including biomass, polymers, and fossil fuels is summarized with close attention to the influences of precursors on the structural evolution of HCs. After a brief introduction of the structural features of HCs, the recent understanding of the structure-performance relationship of HCs for sodium storage is summarized. Then, the main focus is concentrated on the progress of producing HCs from distinct precursors. After that, the pros and cons of HCs derived from different precursors are comprehensively compared to conclude the selection rules of precursors. Finally, the further directions of HCs are deeply discussed to end this review.

Revealing the Na storage behavior of graphite anodes in low-concentration imidazole-based electrolytes

The thermodynamic instability of Na+-intercalated compounds is an important factor limiting the application of graphite anodes in sodium-ion batteries. Although solvent co-intercalation is recognized as a simple and effective strategy, the challenge lies in the lack of durable electrolytes. Herein, we successfully apply low-concentration imidazole-based electrolytes to graphite anodes for sodium-ion batteries. Specifically, low concentrations ensure high ionic conductivity while saving on costs. Methylimidazole molecules can be co-intercalated with Na+, and a small amount of unreleased solvated Na+ serves the dual purpose of providing support to the graphite layer and preventing peeling off. The interphase formed in imidazole is more uniform and dense compared with that in ether electrolytes, which reduces side reactions and the risk of internal short circuits. The obtained battery demonstrates a long cycle life of 1800 cycles with a capacity retention of 84.6%. This success extends to other imidazole-based solvents such as 1-propylimidazole and 1-butylimidazole.

Tartaric Acid Cross-Linking Polyvinyl Alcohol as Degradable Separators for Rechargeable Lithium Ion Batteries

The escalating focus on environmental concerns and the swift advancement of eco-friendly biodegradable batteries raises a pressing demand for enhanced material design in the battery field. The traditional polypropylene (PP) that is monopolistically utilized in the commercial LIBs is hard to recycle. In this work, we prepare a novel water degradable separators via the cross-linking of polyvinyl alcohol (PVA) and dibasic acid (tartaric acid, TA). Through the integration of non-solvent liquid-phase separation, we successfully produced a thermally stable PVA-TA membrane with tunable thickness and a high level of porosity. These specially engineered PVA-TA separators were implemented in LiFePO4 (LFP)|separator|Li cells, resulting in superior multiplicative performance and achieving a capacity of 88 mAh g-1 under 5 C. Additionally, the straightforward small molecule cross-linking technique significantly reduced the crystalline region of the polymer, thereby enhancing ionic conductivity. Notably, after cycling, the PVA-TA separators can be easily dissolved in 95 °C hot water, enabling its reutilization for the production of new PVA-TA separators. Therefore, this work introduces a novel concept to design green and sustainable separators for recyclable lithium batteries.

Molecular Engineering Enabling High Initial Coulombic Efficiency and Rubost Solid Electrolyte Interphase for Hard Carbon in Sodium-Ion Batteries

Hard carbon (HC) as a potential candidate anode for sodium-ion batteries (SIBs) suffers from unstable solid electrolyte interphase (SEI) and low initial Coulombic efficiency (ICE), which limits its commercial applications and urgently requires the emergence of a new strategy. Herein, an organic molecule with two sodium ions, disodium phthalate (DP), was successfully engineered on the HC surface (DP-HC) to replenish the sodium loss from solid electrolyte interphase (SEI) formation. A stabilized and ultrathin (≈7.4 nm) SEI was constructed on the DP-HC surface, which proved to be simultaneously suitable in both ester and ether electrolytes. Compared to pure HC (60.8 %), the as-designed DP-HC exhibited a high ICE of >96.3 % in NaPF6 in diglyme (G2) electrolyte, and is capable of servicing consistently for >1600 cycles at 0.5 A g-1 . The Na3 V2 (PO4 )3 (NVP)|DP-HC full-cell with a 98.3 % exceptional ICE can be cycled stably for 450 cycles, demonstrating the tremendous practical application potential of DP-HC. This work provides a molecular design strategy to improve the ICE of HC, which will inspire more researchers to concentrate on the commercialization progress of HC.

Enhancing Sodium-Ion Energy Storage of Commercial Activated Carbon by Constructing Closed Pores via Ball Milling

Mechanical ball milling is a prevalent technology for material preparation and also serves as a post-treatment method to modify electrode materials, thus enhancing electrochemical performances. This study explores the microstructure modification of commercial activated carbon through mechanical ball milling, proving its efficacy in increasing sodium-ion energy storage. The evolution of activated carbon's physical and chemical properties during ball milling was systematically examined. It was observed that the quantity of closed pores and the graphitization degree in activated carbon increased with extended ball milling duration. The sodium storage mechanism in activated carbon transitions to an insertion-pore filling process, significantly elevating platform capacity. Additionally, ball-milled activated carbon demonstrates remarkable long-term cycling stability (92% capacity retention over 200 cycles at 200 mA g-1) and rate performance. This research offers a novel approach to developing advanced anode materials for sodium-ion batteries.