Anatase TiO2 as a Na+-Storage Anode Active Material for Dual-Ion Batteries

Over-Lithiation Regulation of Silicon-Based Anodes for High-Energy Lithium-Ion Batteries

Mitigating the growth of dendritic lithium (Li) metal on silicon (Si) anodes has become a crucial task for the pursuit of long-term cycling stability of high energy density Si-based lithium-ion batteries (LIBs) under fast charging or other specific conditions. While it is widely known that Li metal plating on Si-based anodes may introduce inferior cycling stability and cause safety concerns, the evolution of the anode/material structure and electrochemical performance with Li metal plating remains largely unexplored. A comprehensive quantitative investigation of the hybrid Li storage mechanism, combining the Li alloying/dealloying mechanism and plating/stripping mechanism, has been conducted to explore the effect of Li plating on Si-based anodes. The findings reveal that Li plating/stripping accounts for the decay of the overall Coulombic efficiency and cycling stability of the hybrid Li storage mechanism. Furthermore, alloying reactions occurring below 0 V encourage the formation of crystalline Li15Si4, which subsequently exacerbates voltage hysteresis. The performance decay is amplified as the ratio of Li plating/stripping capacity increases, or in other words, as the over-lithiation level rises, thereby posing a threat to the battery's cycling stability. These results provide valuable insights into the design of advanced Si-based electrodes for high energy density LIBs.

Sustainable Dual-Ion Batteries beyond Li

The limitations of resources used in current Li-ion batteries may hinder their widespread use in grid-scale energy storage systems, prompting the search for low-cost and resource-abundant alternatives. "Beyond-Li cation" batteries have emerged as promising contenders; however, they confront noteworthy challenges due to the scarcity of suitable host materials for these cations. In contrast, anions, the other crucial component in electrolytes, demonstrate reversible intercalation capacity in specific materials like graphite. The convergence of anion and cation storage has given rise to a new battery technology known as dual-ion batteries (DIBs). This comprehensive review presents the current status, advancements, and future prospects of sustainable DIBs beyond Li. Notably, most DIBs exhibit similar cathode reaction mechanisms involving anion intercalation, while the distinguishing factor lies in the cation types functioning at the anode. Accordingly, the review is organized into sections by various cation types, including Na-, K-, Mg-, Zn-, Ca-, Al-, NH4 + -, and proton-based DIBs. Moreover, a perspective on these novel DIBs is presented, along with proposed protocols for investigating DIBs and promising future research directions. It is envisioned that this review will inspire fresh concepts, ideas, and research directions, while raising important questions to further tailor and understand sustainable DIBs, ultimately facilitating their practical realization.

Conversion-intercalation competing behaviour of halogen storage on graphite electrode from fluid ZnCl2/ZnBr2 hydrates

Zinc-based aqueous dual-ion batteries (ADIBs) with halogen-graphite intercalation compound positive electrodes are among the most competitive candidates for next-generation electrochemical energy storage systems. However, most of the electrolytes employed have been gel-like electrolytes; hence, a fundamental understanding of the halogen storage process using fluid hydrates will be essential for constructing efficient Zn-based ADIBs. Herein, the halogen storage mechanism on a graphite electrode from fluid ZnCl2/ZnBr2 hydrates is studied by experimental and computational methods. The results indicate that the halogen storage mechanism is a competition between conversion and intercalation. Moreover, the macroscopic electrode reaction is determined by both the ion-pair solvation state at the graphite-electrolyte interface and the subsequent reactant supply is influenced by the electrode reaction rate.

Solvation Structure Modulation of High-Voltage Electrolyte for High-Performance K-Based Dual-Graphite Battery

Due to the advantages of dual-ion batteries (DIBs) and abundant resources, potassium-based dual-carbon batteries (K-DCBs) have wide application prospects. However, conventional carbonate ester-based electrolyte systems have obvious drawbacks such as poor oxidation resistance and difficulty in sustaining the anion intercalation process at high voltages, which seriously affect the capacity and cycle performance of K-DCBs. Therefore, a rational design of more efficient novel electrolyte systems is urgently required to realize high-performance K-DCBs. Herein, a solvation structure modulation strategy for the K-DCB electrolyte systems is reported. Consequently, substantial K⁺ ion storage improvement at the graphite anode and enhanced bis(fluorosulfonyl)imide anion (FSI^- ) intercalation capacity at the graphite cathode are successfully realized simultaneously. As a proof-of-concept, the assembled K-DCB exhibited a discharge capacity of 103.4 mAh g^-1 , and after 400 cycles, ≈90% capacity retention is observed. Moreover, the energy density of the K-DCB full cell reached 157.6 Wh kg^-1 , which is the best performance in reported K-DCBs till date. This study demonstrates the effectiveness of solvation modulation in improving the performance of K-DCBs.

Difluoro(oxalato)borate's Role in the Intercalation Behavior of Mixed Anions from Sulfolane

Some previous studies have found the synergistic effect of mixed anions in dual-ion batteries (DIBs). In this work, both lithium tetrafluoroborate (LiBF₄ ) and lithium difluoro(oxalato)borate (LiDFOB) were dissolved in sulfolane (SL) solvent, and the resultant solutions were applied for DIBs. The storage behavior of mixed anions in natural graphite positive electrodes was investigated. In-situ X-ray diffraction measurements revealed both anions could participate in the formation of graphite intercalation compounds. Their evolution followed with the decreasing tendency of discharge capacities as the content of LiDFOB increased in solutions. The exchange of anions was discussed.

Spreading the Landscape of Dual Ion Batteries: from Electrode to Electrolyte

The working mechanism of a dual-ion battery (DIB) differs from that of a lithium-ion battery (LIB) in that the anions in the electrolyte of the former can be intercalated as well. Researchers have been paying close attention to this device because of its high voltage, low price, and environmental friendliness. However, DIBs are still in their early research stages, and numerous issues need to be addressed and investigated further. Initially, this Review explains how DIBs work in principle and discusses the progress of electrode materials for cathode and anode. Furthermore, since the electrolytes used as the active material, as well as anion, solvent, and additives, have a significant impact on the DIB's capacity and voltage, the current status is also presented in terms of electrolytes, followed by an outlook on confronting the challenges. A comprehensive summary from electrode to electrolyte will guide the development of next-generation DIBs.

High Discharge Capacity and Ultra-Fast-Charging Sodium Dual-Ion Battery Based on Insoluble Organic Polymer Anode and Concentrated Electrolyte

Sodium-based dual-ion batteries have shown great promise for large-scale energy storage applications due to their wide operating voltages, environmental friendliness, abundant sodium resources, and low cost, which are widely investigated by researchers. However, the development of high-performance anode materials is a key requirement for the realization of such electrochemical energy storage systems at the practical application level. Carbonaceous anode materials based on intercalation/deintercalation mechanisms typically exhibit low discharge capacities, while metal-based materials based on conversion or alloying reactions show unsatisfactory stability in performance. On the contrary, organic materials display high theoretical capacities due to their flexible molecular structure designability and stable cyclic performance with fast reaction kinetics based on the unique enolization reaction. Herein, we report an organic polymer anode material of polyimide (PNTO), combined with a high-concentration electrolyte; the sodium-based dual-ion battery system constructed exhibits outstanding electrochemical performance. The full battery shows an ultra-high specific discharge capacity of 293.2 mAh g-1 and can be cycled stably for 3200/5600/4100 cycles at ultra-high rates of 60/120/150 C without degradation. Furthermore, the dual-ion battery system demonstrates an extremely low self-discharge rate of 0.03% h-1 and superior fast-charging-slow-discharging performance. It is one of the best performances reported up to now for a dual-ion full battery based on an organic polymer anode. This novel battery system design strategy will facilitate the advancement of high-performance organic-based dual-ion batteries and is expected to be a promising candidate for large-scale energy storage applications.

Sodium-Based Dual-Ion Battery Based on the Organic Anode and Ionic Liquid Electrolyte

Combining the advantages of dual-ion batteries (DIBs) and sodium-ion batteries (SIBs), we herein develop a superior sodium-based dual-ion battery (Na-DIB) based on the PTCDA organic anode and ionic liquid (IL) electrolyte. The system shows the highest specific discharge capacity of 177 mAh g^-1 at 0.5C and excellent capacity retention over 100% at 2C after 200 cycles. Notably, even at an ultrahigh rate of 20C, the battery still maintains a considerable capacity of 60 mAh g^-1 with a coulombic efficiency (CE) close to 100 and 94% capacity retention after 1000 cycles. Moreover, the self-discharge of the system has been investigated and shown to have an extremely low value of 0.18% h^-1. Consequently, this work presents an excellent Na-DIB system, which could be a promising candidate for large-scale applications.

Molecular grafting towards high-fraction active nanodots implanted in N-doped carbon for sodium dual-ion batteries

Sodium-based dual-ion batteries (Na-DIBs) show a promising potential for large-scale energy storage applications due to the merits of environmental friendliness and low cost. However, Na-DIBs are generally subject to poor rate capability and cycling stability for the lack of suitable anodes to accommodate large Na+ ions. Herein, we propose a molecular grafting strategy to in situ synthesize tin pyrophosphate nanodots implanted in N-doped carbon matrix (SnP2O7@N-C), which exhibits a high fraction of active SnP2O7 up to 95.6 wt% and a low content of N-doped carbon (4.4 wt%) as the conductive framework. As a result, this anode delivers a high specific capacity ∼400 mAh g-1 at 0.1 A g-1, excellent rate capability up to 5.0 A g-1 and excellent cycling stability with a capacity retention of 92% after 1200 cycles under a current density of 1.5 A g-1. Further, pairing this anode with an environmentally friendly KS6 graphite cathode yields a SnP2O7@N-C||KS6 Na-DIB, exhibiting an excellent rate capability up to 30 C, good fast-charge/slow-discharge performance and long-term cycling life with a capacity retention of ∼96% after 1000 cycles at 20 C. This study provides a feasible strategy to develop high-performance anodes with high-fraction active materials for Na-based energy storage applications.

A TiSe2 -Graphite Dual Ion Battery: Fast Na-Ion Insertion and Excellent Stability

The sodium dual ion battery (Na-DIB) technology is proposed as highly promising alternative over lithium-ion batteries for the stationary electrochemical energy-storage devices. However, the sluggish reaction kinetics of anode materials seriously impedes their practical implementation. Herein, a Na-DIB based on TiSe₂ -graphite is reported. The high diffusion coefficient of Na-ions (3.21×10^-11 -1.20×10^-9  cm²  s^-1 ) and the very low Na-ion diffusion barrier (0.50 eV) lead to very fast electrode kinetics, alike in conventional surface capacitive storage systems. In-situ investigations reveal that the fast Na-ion diffusion involves four insertion stage compositions. A prototype cell shows a reversible capacity of 81.8 mAh g^-1 at current density of 100 mA g^-1 , excellent stability with 83.52 % capacity retention over 200 cycles and excellent rate performance, suggesting its potential for next-generation large scale high-performance stationary energy storage systems.

Sponge-like NaFe2PO4(SO4)2@rGO as a high-performance cathode material for sodium-ion batteries

Sponge-like NaFe₂PO₄(SO₄)₂@reduced graphene oxide composite is prepared as cathode material for sodium-ion batteries. The corresponding full cells matched with hard carbon anode exhibit favorable rate and cyclic performance.

Efficient Na+-storage in a Li4Ti5O12 anode to expand the voltage-window for full SIBs of high energy density

The stable storage of sodium ions always presents some difficulties for sodium-based dual-ion batteries (S-DIBs), such as the irreversibility of guest-storage and kinetic hindrance in the anode. Based on the low strain volume and stable phase structure, herein, lithium titanate (LTO, Li₄Ti₅O₁₂) was developed to store sodium ions between the working potential (∼0.8 V), which expands the lower plateau over than that of lithium ion storage (∼1.55 V) to obtain a high energy density of full batteries. The spinel lithium titanate shows negligible volume change and extremely stable structure under Na⁺-storage, which completely overcomes the shortage problems of the Na⁺-host. Additionally, by the detection of the transfer state of anions and cations in dual-ion batteries, the diffusion coefficient of the sodium ion in the LTO electrode is higher than that of the cathode, which shows that the transport process of sodium ions can meet the kinetic demands of full batteries. Such S-DIBs exhibit a large working voltage of 2.0–4.6 V and stable electrochemical performance over 1280 cycles, which is superior to conventional sodium-based systems, and further exhibit many advantages such as high energy density, environmental friendliness, and low cost.

The stable storage of sodium ions always presents some difficulties for sodium-based dual-ion batteries (S-DIBs), such as the irreversibility of guest-storage and kinetic hindrance in the anode.

Anion Intercalation into a Graphite Electrode from Trimethyl Phosphate

Trimethyl phosphate (TMP) is a flame-retardant solvent frequently used in nonaqueous electric energy storage devices. Anions can hardly intercalate into a graphite positive electrode from neat TMP at ordinary conditions. In TMP solutions, dissolving lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonimide) (LiTFSI), by means of increasing lithium salt concentration or increasing the charge cutoff voltage of Li/graphite cells, the TMP-solvated anions can successfully intercalate into graphite positive electrodes. Moreover, the effect of TFSI^- activation on a graphite electrode is addressed. Ex situ X-ray diffraction measurements in combination with traditional electrochemical tests are employed to investigate the crystal structure change and electrochemical performance of graphite electrodes, respectively. Nuclear magnetic resonance, Fourier-transform infrared, and Raman spectroscopy are employed to characterize the TMP solutions.

A dual-ion battery has two sides: the effect of ion-pairs

Interplay between the intercalation of Li⁺ into Li₄Ti₅O₁₂ and BF₄⁻ into graphite in a dual-ion battery is studied.