CMC-citric acid Cu(II) cross-linked binder approach to improve the electrochemical performance of Si-based electrodes

Metal ion removal using a low-cost coconut shell activated carbon bioadsorbent in the recovery of lactic acid from the fermentation broth

Downstream recovery and purification of lactic acid from the fermentation broth using locally available, low-cost materials derived from agricultural residues was demonstrated herein. Surface modification of coconut shell activated carbon (CSAC) was performed by grafting with carboxymethyl cellulose (CMC) using citric acid (CA) as the crosslinking agent. A proper ratio of CMC and CA to CSAC and grafting time improved the surface functionalization of grafted nanostructured CMC-CSAC while the specific surface area and porosity remained unchanged. Lactic acid was partially purified (78%) with the recovery percentage of lactic acid at 96% in single-stage adsorption at room temperature and pH 6 with a 10:1 ratio of cell-free broth to CMC-CSAC bioadsorbent. A thermodynamic study revealed that the adsorption was exothermic and non-spontaneous while the Langmuir isotherm model explained the adsorption phenomena. The results in this study represented the potential of waste utilization as solid adsorbents in green and low-cost adsorption technology.

Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Li-Ion Batteries: Beneficial Impact on Mechanical Properties and Electrochemical Performance

A simple and versatile preparation of Zn(II)-poly(carboxylates) reticulated binders by the addition of Zn(II) precursors (ZnSO₄, ZnO, or Zn(NO₃)₂) into a preoptimized poly(carboxylic acids) binder solution is proposed. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes. The formation of carboxylate-Zn(II) coordination bonds formation is investigated by rheology and FTIR and NMR spectroscopies. Mechanical characterizations reveal that the coordinated binder offers a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in the presence of a carbonate solvent (i.e., in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure. Such coordinatively reticulated electrodes outperform their uncoordinated counterparts with an improved capacity retention of over 30% after 60 cycles.

Nanoscale Morphological Characterization of Coordinated Binder and Solid Electrolyte Interphase in Silicon-Based Electrodes for Li-Ion Batteries

The physical crosslinking of polymeric binders through coordination chemistry significantly improves the electrochemical performance of silicon-based negative electrodes. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy is used to probe the nanoscale morphology of such electrodes. This technique reveals the homogeneous coordination of carboxylated binder with Zn cations and its layering on the silicon surface. The solid electrolyte interphase (SEI) formed after the first cycle is denser with Zn-coordinated binder and preferentially observed on binder-depleted zones. The superiority of coordinated binders can be attributed to their capacity to better stabilize the electrode and the SEI layer due to improved mechanical properties. This results in a lower SEI impedance, a higher first cycle coulombic efficiency, and a 40% improvement of capacity retention after 50 cycles for highly loaded electrodes of over 6 mAh cm^-2 .

Key Factors for Binders to Enhance the Electrochemical Performance of Silicon Anodes through Molecular Design

Silicon is considered the most promising candidate for anode material in lithium-ion batteries due to the high theoretical capacity. Unfortunately, the vast volume change and low electric conductivity have limited the application of silicon anodes. In the silicon anode system, the binders are essential for mechanical and conductive integrity. However, there are few reviews to comprehensively introduce binders from the perspective of factors affecting performance and modification methods, which are crucial to the development of binders. In this review, several key factors that have great impact on binders' performance are summarized, including molecular weight, interfacial bonding, and molecular structure. Moreover, some commonly used modification methods for binders are also provided to control these influencing factors and obtain the binders with better performance. Finally, to overcome the existing problems and challenges about binders, several possible development directions of binders are suggested.

Influence of the Polyacrylic Acid Binder Neutralization Degree on the Initial Electrochemical Behavior of a Silicon/Graphite Electrode

The role of the physicochemical properties of the water-soluble polyacrylic acid (PAA) binder in the electrochemical performance of highly loaded silicon/graphite 50/50 wt % negative electrodes has been examined as a function of the neutralization degree x in PAAH_1-xLi_x at the initial cycle in an electrolyte not containing ethylene carbonate. Electrode processing in the acidic PAAH binder at pH 2.5 leads to a deep copper corrosion, resulting in a significant electrode cohesion and adhesion to the current collector surface, but the strong binder rigidity may explain the big cracks occurring on the electrode surface at the first cycle. The nonuniform binder coating on the material surface leads to an important degradation of the electrolyte, explaining the lowest initial Coulombic efficiency and the lowest reversible capacity among the studied electrodes. When processed in neutral pH, the PAAH_0.22Li_0.78 binder forms a conformal artificial solid electrolyte interphase layer on the material surface, which minimizes the electrolyte reduction at the first cycle and then maximizes the initial Coulombic efficiency. However, the low mechanical resistance of the electrode and its strong cracking explain its low reversible capacity. Electrodes prepared at intermediate pH 4 combine the positive assets of electrodes prepared at acidic and neutral pH. They lead to the best initial performance with a notable areal capacity of 7.2 mA h cm^-2 and the highest initial Coulombic efficiency of around 90%, a value much larger than the usual range reported for silicon/graphite anodes. All data obtained with complementary characterization techniques were discussed as a function of the PAA polymeric chain molecular conformation, microstructure, and surface adsorption or grafting, emphasizing the tremendous role of the binder in the electrode initial performance.