High-Rate and Long-Cycle Cathode for Sodium-Ion Batteries: Enhanced Electrode Stability and Kinetics via Binder Adjustment

Engineering Alkali Lignin Structure Modification: Enhanced Hard Carbon Electrolyte Interface Toward Practical Sodium Ion Batteries

Hard carbon (HC) exhibits great potential as a promising candidate for sodium-ion batteries owing to its inherent advantages. However, the main challenges in utilizing HC stem from its low initial coulombic efficiency (ICE) and poor rate performance caused by its excessive surface defects. In this study, an effective strategy of employing alkali lignin (AL) is proposed, derived from pulp waste, as a binder for HC to create a uniform and inorganically enriched solid electrolyte interface. AL can modify the surface defects of HC through strong π-π interactions between the aromatic ring of AL and HC, while ingeniously grafting abundant active ─OH and ─COOH groups onto the electrode surface. The strong binder force between AL and electrolyte salts facilitates the formation of an ultra-thin NaF-rich solid electrolyte interface (SEI) layer (10 nm), thereby achieving an exceptional ICE of 91%. Furthermore, owing to its electrochemical activity, AL enables HC anode to exhibit an increasing slope capacity during cycling, compensating for capacity decay at high current densities. Consequently, when assembled into a full battery configuration, excellent rate performance is achieved with a reversible capacity of 282 mAh g-1 even at a current density of 5A g-1.

A Robust Network Sodium Carboxymethyl Cellulose-Epichlorohydrin Binder for Silicon Anodes in Lithium-Ion Batteries

Silicon (Si), as an ideal anode component for lithium-ion batteries, is susceptible to substantial volume changes, leading to pulverization and excessive electrolyte consumption, ultimately resulting in a rapid decline in the cycle stability. Herein, a new sodium carboxymethyl cellulose-epichlorohydrin (CMC-ECH) binder featuring a three-dimensional (3D) network cross-linked structure is synthesized by a simple ring-opening reaction, which can effectively bond the Si anode through abundant covalent and hydrogen bonds to mitigate its pulverization. Benefitting from the merits of the CMC-ECH binder, the electrochemical performance is significantly enhanced compared to the CMC binder. The CMC-ECH binder is applied to Si anodes, a specific capacity of 1054.2 mAh g-1 can be maintained at 0.2 C following 200 cycles under an elevated Si mass loading of around 1.0 mg cm-2, and the corresponding capacity retention is 65.6%. In the case of the LiFePO4//Si@CMC-ECH full battery, the cycle stability exhibits a substantial enhancement compared with the LiFePO4//Si@CMC full battery. Furthermore, the CMC-ECH binder demonstrates compatibility with micron-Si anode materials. Based on the above, we have successfully developed a facilely prepared water-based CMC-ECH binder that is suitable for Si and micron-Si anodes in lithium-ion batteries.

Hybrid Binder Chemistry with Hydrogen-Bond Helix for High-Voltage Cathode of Sodium-Ion Batteries

Since sodium-ion batteries (SIBs) have become increasingly commercialized in recent years, Na3V2(PO4)2O2F (NVPOF) offers promising economic potential as a cathode for SIBs because of its high operating voltage and energy density. According to reports, NVPOF performs poorly in normal commercial poly(vinylidene fluoride) (PVDF) binder systems and performs best in combination with aqueous binder. Although in line with the concept of green and sustainable development for future electrode preparation, aqueous binders are challenging to achieve high active material loadings at the electrode level, and their relatively high surface tension tends to cause the active material on the electrode sheet to crack or even peel off from the collector. Herein, a cross-linkable and easily commercial hybrid binder constructed by intermolecular hydrogen bonding (named HPP) has been developed and utilized in an NVPOF system, which enables the generation of a stable cathode electrolyte interphase on the surface of active materials. According to theoretical simulations, the HPP binder enhances electronic/ionic conductivity, which greatly lowers the energy barrier for Na+ migration. Additionally, the strong hydrogen-bond interactions between the HPP binder and NVPOF effectively prevent electrolyte corrosion and transition-metal dissolution, lessen the lattice volume effect, and ensure structural stability during cycling. The HPP-based NVPOF offers considerably improved rate capability and cycling performance, benefiting from these benefits. This comprehensive binder can be extended to the development of next-generation energy storage technologies with superior performance.

Breaking Barriers: Binder-Assisted NiS/NiS2 Heterostructure Anode with High Initial Coulombic Efficiency for Advanced Sodium-Ion Batteries

Developing sodium-ion batteries (SIBs) with high initial coulombic efficiency (ICE) and long-term cycling stability is crucial to meet energy storage device requirements. Designing anode materials that could exhibit high ICE is a promising strategy to realize enhanced energy density in SIBs. A trifunctional network binder substantially improves the electrochemical performance and ICE, providing excellent mechanical properties and strong adhesion strength. A rationally designed electrode material and binder can achieve high ICE, long cycling performance, and excellent specific capacity. Here, a NiS/NiS2 heterostructure as an anode material and a trifunctional network binder (SA-g-PAM) are designed for SIBs. Unprecedently, the anode comprising of an SA-g-PAM binder achieved the highest ICE of 90.7% and remarkable cycling stability for 19000 cycles at a current density of 10 A g-1 and maintained the specific capacity of 482.3 mAh g-1 even after 19000 cycles. This exciting work provides an alternate direction to the battery industry for developing high-performance electrode materials and binders with high ICE and excellent cycling stability for energy storage devices.

Cathode-Electrolyte Interface Modification by Binder Engineering for High-Performance Aqueous Zinc-Ion Batteries

A stable cathode-electrolyte interface (CEI) is crucial for aqueous zinc-ion batteries (AZIBs), but it is less investigated. Commercial binder poly(vinylidene fluoride) (PVDF) is widely used without scrutinizing its suitability and cathode-electrolyte interface (CEI) in AZIBs. A water-soluble binder is developed that facilitated the in situ formation of a CEI protecting layer tuning the interfacial morphology. By combining a polysaccharide sodium alginate (SA) with a hydrophobic polytetrafluoroethylene (PTFE), the surface morphology, and charge storage kinetics can be confined from diffusion-dominated to capacitance-controlled processes. The underpinning mechanism investigates experimentally in both kinetic and thermodynamic perspectives demonstrate that the COO- from SA acts as an anionic polyelectrolyte facilitating the adsorption of Zn2+ ; meanwhile fluoride atoms on PTFE backbone provide hydrophobicity to break desolvation penalty. The hybrid binder is beneficial in providing a higher areal flux of Zn2+ at the CEI, where the Zn-Birnessite MnO2 battery with the hybrid binder exhibits an average specific capacity 45.6% higher than that with conventional PVDF binders; moreover, a reduced interface activation energy attained fosters a superior rate capability and a capacity retention of 99.1% in 1000 cycles. The hybrid binder also reduces the cost compared to the PVDF/NMP, which is a universal strategy to modify interface morphology.

Understanding the Aging Mechanism of Na-Based Layered Oxide Cathodes with Different Stacking Structures

Manganese-based layered oxides are one of the most promising cathodes for Na-ion batteries, but the prospect of their practical application is challenged by high sensitivity to ambient air. The stacking structure of materials is critical to the aging mechanism between layered oxides and air, but there remains a lack of systematic study. Herein, comprehensive research on model materials P-type Na0.50MnO2 and O-type Na0.85MnO2 reveals that the O-phase displays a much higher dynamic affinity toward moisture air compared to P-type compounds. For air-exposed O-type material, Na+ ions are extracted from the crystal lattice to form alkaline species at the surface in contact with air, accompanying by the increase of the valence state of transition metals. The series of undesired reactions result in an increase of interfacial resistance and huge capacity loss. Comparatively, the insertion of H2O into the Na layer is the main reaction during air-exposure of P-type material, and the inserted H2O can be extracted by high-temperature treatment. The H2O de/insertion process not only causes no performance degradation but also can enlarge the interlayer distance. With these understandings, we further propose a washing-resintering strategy to recover the performance of aged O-type materials and an aging strategy to build high-performance P-type materials.

Binders for sodium-ion batteries: progress, challenges and strategies

Binders as a bridge in electrodes can bring various components together thus guaranteeing the integrity of electrodes and electronic contact during battery cycling. In this review, we summarize the recent progress of traditional binders and novel binders in the different electrodes of SIBs. The challenges faced by binders in terms of bond strength, wettability, thermal stability, conductivity, cost, and environment are also discussed in details. Correspondingly, the designing principle and advanced strategies of future research on SIB binders are also provided. Moreover, a general conclusion and perspective on the development of binder design for SIBs in the future are presented.

[Co3(μ3-O)]-Based Metal-Organic Frameworks as Advanced Anode Materials in K- and Na-Ion Batteries

A new metal-organic framework {(Me₂NH₂)₂[Co₃(μ₃-O)(btb)₂(py)(H₂O)]·(DMF)₂(H₂O)₂}_n (Cobtbpy) was solvothermal synthesized (H₃btb = 1,3,5-tri(4-carboxylphenyl)benzene, py = pyridine, DMF = N,N-dimethylformamide). Cobtbpy shows a (3,6)-connected rtl 3D network with a point symbol of (4·6²)₂(4²·6¹⁰·8³) based on the [Co₃(μ₃-O)] clusters. The obtained Cobtbpy has stable, accessible, dense active sites and can be applied in the potassium- and sodium-ion batteries. Through mixing with single-walled carbon nanotubes, the prepared composite anode material Cobtbpy-0.9 achieved a high reversible capability, delivering 416 mAh/g in the potassium-ion batteries and 379 mAh/g in the sodium-ion batteries at 0.05 A/g. The outstanding properties of Cobtbpy-0.9 in the batteries demonstrated that this MOFs-based carbon composite is a highly desirable electrode material candidate for high-performance potassium- and sodium-ion batteries.

Novel Lamellar Tetrapotassium Pyromellitic Organic for Robust High-Capacity Potassium Storage

Redox-active organics are investigation hotspots for metal ion storage due to their structural diversity and redox reversibility. However, they are plagued by limited storage capacity, sluggish ion diffusion kinetics, and weak structural stability, especially for K⁺ ion storage. Herein, we firstly reported the lamellar tetrapotassium pyromellitic (K₄ PM) with four active sites and large interlayer distance for K⁺ ion storage based on a design strategy, where organics are constructed with the small molecular mass, multiple active sites, fast ion diffusion channels, and rigid conjugated π bonds. The K₄ PM electrode delivers a high capacity up to 292 mAh g^-1 at 50 mA g^-1 , among the best reported organics for K⁺ ion storage. Especially, it achieves an excellent rate capacity and long-term cycling stability with a capacity retention of ≈83 % after 1000 cycles. Incorporating in situ and ex-situ techniques, the K⁺ ion storage mechanism is revealed, where conjugated carboxyls are reversibly rearranged into enolates to stably store K⁺ ions. This work sheds light on the rational design and optimization of organic electrodes for efficient metal ion storage.