Highly Stable and High Rate-Performance Na-Ion Batteries Using Polyanionic Anthraquinone as the Organic Cathode

Mitigating Jahn-Teller Effects: First-Principles and experimental study of aluminium-doped manganese-based NASICON cathodes for Sodium-Ion batteries

Manganese-based structures have been widely studied as candidates for cathode materials in sodium-ion batteries (SIBs) owing to their low-cost and environmental-friendly properties. However, due to the orbital properties of Mn3+, the Jahn-Teller effect occurs frequently during the electrode reaction, leading to irreversible phase transition of the structure with capacity degradation. Here, we mitigated this critical issue by a theory-guided synthesis of aluminium-doped manganese-based NASICON-type phosphate cathode Na4MnAl(PO4)3. Using density functional theory, we have predicted its electrode properties, including the phase stability, voltage plateau and ionic diffusion properties, which results supported favor physicochemical properties and fast kinetics behavior. Moreover, Na4MnAl(PO4)3 exhibited structural stability and small volume change (6.2 %) during theoretical cycling process, and the detrimental Jahn-Teller effect was effectively suppressed analyzed by Bader charge. With two effective redox pairs, i.e., Mn4+/Mn3+ (4.1 V) and Mn3+/Mn2+ (3.6 V), Na4MnAl(PO4)3 achieved a capacity retention of 85.08 % after 500 cycles at 5C. Moreover, this cathode was well compatible to hard carbon and achieved 81.8 % capacity retention after 200 cycles at 1C. This work suggests its high energy density and excellent cycling stability, which provides a critical reference from theoretical design to experimental study for the manganese-based phosphate cathode for high-performance SIBs.

Dual Intermediates in C-C Coupling Reactions and High-Performance Sodium-Iodine Batteries: In Situ Generated Quasi-Graphene in Anthraquinone-Inserted Layered Double Hydroxide

Na-I2 batteries are a cost-effective alternative to conventional energy storage technologies. However, their development is hindered by highly soluble polyiodides and sluggish redox kinetics. Herein, the issues are solved by a 1,8-dianthraquinone (AQ)-inserted layered double hydroxide (CoNi LDH-AQ) formulated as Co1.65Ni4.35(CO3)1.5(OH)3(AQ)3, whose interlayer channel not only immobilizes polyiodides but also acts as a confined vessel for the C-C couplings of AQ into functionalized quasi-graphene (F-GO). The in situ generated I+ not only promotes the I-/I2/I+ multielectron conversion to boost redox kinetics, eliminate shuttle effect, and achieve superior capacities/lifespans but also accelerates the couplings of AQ with low barriers. The work proposes a two-in-one strategy, which combines inorganic and organic reactions together with the same intermediate. It provides a routine to synthesize quasi-graphene based on the couplings of small organic species in a confined space to suppress aggregation. And the good conductivity of quasi-graphene in turn facilitates electron transfer in Na-I2 batteries.

Small-molecule organic electrode materials on carbon-coated aluminum foil for high-performance sodium-ion batteries

Organic molecular electrode materials are promising candidates in batteries. However, direct application of small molecule materials usually suffers from drastic capacity decay and inefficient utilization of active materials because of their high solubility in organic electrolytes and low electrical conductivity. Herein, a simple strategy is found to address the above issues through coating the small-molecule organic materials on a commercialized carbon-coated aluminum foil (CCAF) as the enhanced electrode. Both the experimental and calculation results confirm that the relatively rough carbon coating on the aluminum foil not only exhibits superior adsorption capacity of small-molecule organic electrode materials with a tight contact interface but also provides continuous electronic conduction channels for the facilitated charge transfer and accelerated reaction kinetics. In addition, the carbon coating also inhibits Al corrosion in electrochemical process. As a result, by using the tetrahydroxy quinone-fused aza-phenazine (THQAP) molecule as an example, the THQAP-CCAF electrode exhibits an excellent rate performance with a high capacity of 220 and 180 mAh g-1 at 0.1 and 2 A/g, respectively, and also a remarkable cyclability with a capacity retention of 77.3% even after 1700 cycles in sodium-ion batteries. These performances are much more superior than that of batteries with the THQAP on bare aluminum foil (THQAP-AF). This work provides a substantial step in the practical application of the small-molecule organic electrode materials for future sustainable batteries.

Predicting the Solubility of Organic Energy Storage Materials Based on Functional Group Identity and Substitution Pattern

Organic electrode materials (OEMs) provide sustainable alternatives to conventional electrode materials based on transition metals. However, the application of OEMs in lithium-ion and redox flow batteries requires either low or high solubility. Currently, the identification of new OEM candidates relies on chemical intuition and trial-and-error experimental testing, which is costly and time intensive. Herein, we develop a simple empirical model that predicts the solubility of anthraquinones based on functional group identity and substitution pattern. Within this statistical scaffold, a training set of 18 anthraquinone derivatives allows us to predict the solubility of 808 quinones. Internal and external validations show that our model can predict the solubility of anthraquinones in battery electrolytes within log S ± 0.7, which is a much higher accuracy than existing solubility models. As a demonstration of the utility of our approach, we identified several new anthraquinones with low solubilities and successfully demonstrated their utility experimentally in Li-organic cells.

Recent Progress on Graphene-Based Nanocomposites for Electrochemical Sodium-Ion Storage

In advancing battery technologies, primary attention is paid to developing and optimizing low-cost electrode materials capable of fast reversible ion insertion and extraction with good cycling ability. Sodium-ion batteries stand out due to their inexpensive price and comparable operating principle to lithium-ion batteries. To achieve this target, various graphene-based nanocomposites fabricate strategies have been proposed to help realize the nanostructured electrode for high electrochemical performance sodium-ion batteries. In this review, the graphene-based nanocomposites were introduced according to the following main categories: graphene surface modification and doping, three-dimensional structured graphene, graphene coated on the surface of active materials, and the intercalation layer stacked graphene. Through one or more of the above strategies, graphene is compounded with active substances to prepare the nanocomposite electrode, which is applied as the anode or cathode to sodium-ion batteries. The recent research progress of graphene-based nanocomposites for SIBs is also summarized in this study based on the above categories, especially for nanocomposite fabricate methods, the structural characteristics of electrodes as well as the influence of graphene on the performance of the SIBs. In addition, the relevant mechanism is also within the scope of this discussion, such as synergistic effect of graphene with active substances, the insertion/deintercalation process of sodium ions in different kinds of nanocomposites, and electrochemical reaction mechanism in the energy storage. At the end of this study, a series of strategies are summarized to address the challenges of graphene-based nanocomposites and several critical research prospects of SIBs that provide insights for future investigations.

Mechanism of gelation in high nickel content cathode slurries for sodium-ion batteries

Sodium-ion batteries are a prospective sustainable alternative to the ubiquitous lithium-ion batteries due to the abundancy of sodium, and their cobalt free cathodes. The high nickel O3-type oxides show promising energy densities, however, a time dependency in the rheological properties of the composite electrode slurries is observed, which leads to inhomogeneous coatings being produced. A combination of electron microscopy and infra-red spectroscopy were used to monitor the O3-oxide surface changes upon exposure to air, and the effect upon the rheology and stability of the inks was investigated. Upon exposure to air, NaOH rather than Na₂CO₃ was observed on the surfaces of the powder through FTIR and EDS. The subsequent gelation of the slurry was initiated by the NaOH and dehydrofluorination with crosslinking of PVDF was observed through the reaction product, NaF. Approximately 15% of the CF bonds in PVDF undergo this dehydrofluorination to form NaF. As observed in the relaxation time of fitted rheological data, the gelation undergoes a three-stage process: a dehydrofluorination stage, creating saturated structures, a crosslinking stage, resulting in the highest rate of gelation, and a final crosslinking stage. This work shows the mechanism for instability of high nickel containing powders and electrode slurries, and presents a new time dependent oscillatory rheology test that can be used to determine the process window for these unstable slurry systems.

Soluble Organic Cathodes Enable Long Cycle Life, High Rate, and Wide-Temperature Lithium-Ion Batteries

Organic electrode materials free of rare transition metal elements are promising for sustainable, cost-effective, and environmentally benign battery chemistries. However, severe shuttling effect caused by the dissolution of active materials in liquid electrolytes results in fast capacity decay, limiting their practical applications. Here, using a gel polymer electrolyte (GPE) that is in situ formed on Nafion-coated separators, the shuttle reaction of organic electrodes is eliminated while maintaining the electrochemical performance. The synergy of physical confinement by GPE with tunable polymer structure and charge repulsion of the Nafion-coated separator substantially prevents the soluble organic electrode materials with different molecular sizes from shuttling. A soluble small-molecule organic electrode material of 1,3,5-tri(9,10-anthraquinonyl)benzene demonstrates exceptional electrochemical performance with an ultra-long cycle life of 10 000 cycles, excellent rate capability of 203 mAh g^-1 at 100 C, and a wide working temperature range from -70 to 100 °C based on the solid-liquid conversion chemistry, which outperforms all previously reported organic cathode materials. The shielding capability of GPE can be designed and tailored toward organic electrodes with different molecular sizes, thus providing a universal resolution to the shuttling effect that all soluble electrode materials suffer.

A Low-Cost Na-Ion and K-Ion Batteries Using a Common Organic Cathode and Bismuth Anode

Molecule-aggregation organic electrodes in principle have the capability for "single-molecule-energy-storage" in metal-ion rechargeable batteries, which indicates that the same organic electrode can be simultaneously applied to multiple metal-ion rechargeable batteries. In this study, the polyanionic organic compound 9,10-anthraquinone-2,6-disulfonate (Na₂ AQ26DS, 130 mAh g^-1 ) is used as a common cathode and metal bismuth (Bi) as a common anode to simultaneously assemble low-cost Na-ion and K-ion full cells. The Na-ion full cells can deliver the peak discharge capacity of 139 mAh g^-1 _cathode at 0.5-3.0 V, and the K-ion full cells can show the peak discharge capacity of 130 mAh g^-1 _cathode at 0.5-3.0 V. These results are comparable to the best organic-based Na-ion and K-ion full cells reported to date.

Electrolyte Effect on a Polyanionic Organic Anode for Pure Organic K-Ion Batteries

Potassium naphthalene-1,4,5,8-tetracarboxylate (K₄NTC, 117 mAh g^-1) is a new organic anode for K-ion batteries, which possesses four strong K-O ionic bonds within a -4-valent naphthalene-1,4,5,8-tetracarboxylate skeleton (NTC^4-). And thus, K₄NTC is a polyanionic organic salt. Simultaneously, new insights are provided by comparing two typical electrolyte systems (carbonate and ether electrolytes) with KPF₆ as the same solute. Finally, the pure organic K-ion batteries (OKIBs) are fabricated by using perylene-3,4,9,10-tetracarboxydianhydride (PTCDA) as the organic cathode and the reduced state (K₆NTC) of K₄NTC as the anode. And this OKIB can deliver a peak discharge capacity of 121 mAh g^-1_anode and run over 1500 cycles in 0.5-3 V using ether electrolytes.

Atomistic Observation of Desodiation-Induced Phase Transition in Sodium Tungsten Bronze

The phase instability in layered-structure Na_0.5WO_3.25 induced by the extraction of Na ions was investigated by applying transmission electron microscopy. Real-time atomic-scale observation reveals the phase transition pathway: Na_0.5WO_3.25 (triclinic) → Na_xWO₃ (cubic) → WO₃ (monoclinic) with specific orientation relationships. The dynamic evolution of Na_0.5WO_3.25/Na_xWO₃ phase boundaries shows that Na_0.5WO_3.25 will cleave along the (100)_T and (010)_T and recrystallize as (101)_C and (010)_C of Na_xWO₃, respectively. The phase transition pathway can be well-explained according to the structural characteristics in the three phases. By better understanding of the phase instability induced by the extraction of Na ions in possible layered-structure cathode materials, this work provides a reference for the design of sophisticated strategies toward high-performance Na-ion batteries.

Analysis of the Ordering Effects in Anthraquinone Thin Films and Its Potential Application for Sodium Ion Batteries

The ordering effects in anthraquinone (AQ) stacking forced by thin-film application and its influence on dimer solubility and current collector adhesion are investigated. The structural characteristics of AQ and its chemical environment are found to have a substantial influence on its electrochemical performance. Computational investigation for different charged states of AQ on a carbon substrate obtained via basin hopping global minimization provides important insights into the physicochemical thin-film properties. The results reveal the ideal stacking configurations of the individual AQ-carrier systems and show ordering effects in a periodic supercell environment. The latter reveals the transition from intermolecular hydrogen bonding toward the formation of salt bridges between the reduced AQ units and a stabilizing effect upon the dimerlike rearrangement, while the strong surface-molecular interactions in the thin-film geometries are found to be crucial for the formed dimers to remain electronically active. Both characteristics, the improved current collector adhesion and the stabilization due to dimerization, are mutual benefits of thin-film electrodes over powder-based systems. This hypothesis has been further investigated for its potential application in sodium ion batteries. Our results show that AQ thin-film electrodes exhibit significantly better specific capacities (233 vs 87 mAh g-1 in the first cycle), Coulombic efficiencies, and long-term cycling performance (80 vs 4 mAh g-1 after 100 cycles) over the AQ powder electrodes. By augmenting the experimental findings via computational investigations, we are able to suggest design strategies that may foster the performance of industrially desirable powder-based electrode materials.

Analytical Measurements to Elucidate Structural Behavior of 2,5-Dimethoxy-1,4-benzoquinone During Charge and Discharge

Organic compounds as electrode materials can contribute to sustainability because they are nontoxic and environmentally abundant. The working mechanism during charge-discharge for reported organic compounds as electrode materials is yet to be completely understood. In this study, the structural behavior of 2,5-dimethoxy-1,4-benzoquinone (DMBQ) during charge-discharge is investigated by using NMR spectroscopy, energy-dispersive X-ray spectroscopy, magnetic measurements, operando Raman spectroscopy, and operando X-ray diffraction. For both lithium and sodium systems, DMBQ works as a cathode accompanied with the insertion and deinsertion of Li and Na ions during charge-discharge processes. The DMBQ sample is found to be in two-phase coexistence state at the higher voltage plateau, and the radical monoanion and dianion phases have no long-distance ordering. These structures reversibly change into the original neutral phase with long-distance ordering. These techniques can show the charge-discharge mechanism and the factors that determine the deterioration of organic batteries, thus guiding the design of future high-performance organic batteries.

Long-lifespan Polyanionic Organic Cathodes for Highly Efficient Organic Sodium-ion Batteries

An organic Na-ion battery is reported with a polyanionic 9,10-anthraquinone-2,6-disulfonate (Na₂ AQ26DS, 130 mAh g^-1 ) cathode and the Na-intercalated state (Na₄ TP) of sodium terephthalate (Na₂ TP, 255 mAh g^-1 ) as the anode. The resulting full cells deliver the maximum discharge capacity of 131 mAh g^-1 _cathode in 0.5-3.2 V, simultaneously maintaining the average value of ≈62 mAh g^-1 _cathode during 1200 cycles (0.5 A g^-1 , ≈4 C). These results are among the best performing organic sodium-ion full cells reported to date.

Recent Advances of Two-Dimensional (2 D) MXenes and Phosphorene for High-Performance Rechargeable Batteries

The design and development of advanced electrode materials for high-performance rechargeable batteries have been subjected to extensive studies. Very recently, two-dimensional (2 D) nanomaterials have become promising candidates for batteries, owing to their unique physicochemical properties. In particular, MXenes and phosphorene, which exhibit tailored electrical conductivity and ion storage capability, have attracted increasing attention. This Review presents a comprehensive summary of recent advances in the development of 2 D MXenes and phosphorene as electrode materials for high-performance batteries. Their physicochemical properties, including structural configurations and electronic properties of MXenes and direct band gap and anisotropic properties of phosphorene, are firstly discussed. Then, synthesis methods of the two materials are introduced. Thereafter, their applications as electrode materials in batteries, including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), lithium-sulfur (Li-S) batteries, and metal-air batteries, are summarized and discussed in detail. An emphasis is placed on analyzing performance enhancement mechanisms to elucidate fundamental understanding. Finally, future challenges and opportunities for MXenes and phosphorene as electrode materials for batteries are considered.

A Calcium Organic Salt/rGO composite with Low Solubility and High Conductivity as a Sustainable Anode for Sodium-Ion Batteries

Organic electrodes hold great promise for sustainable electrodes in sodium-ion batteries (SIBs) owing to their easy availability from biomass. However, traditional organic electrodes suffer from two inherent problems, high solubility in organic electrolytes and low electronic conductivity. Here, a calcium organic salt, Cabpdc (bpdc=4,4'-biphenyldicarboxylate) was designed and formed into a composite with reduced graphene oxide (rGO) to improve these two problems by a "two-in-one" approach. As expected, the Cabpdc/rGO composite displayed competitive cycle and rate performances as an anode for SIBs. Additionally, all-organic sodium-ion full cells were successfully fabricated combining this anode with a commercial organic cathode, promising applications for sustainable SIBs.