ABSTRACT
The intrinsic volumetric stress during cycling is the main obstacle for developing Si-based materials as high-energy-density lithium-ion battery anodes. Elastic binders have been demonstrated as an efficient approach to alleviate the stress of Si. Herein, we design a tough 3D hard/soft polymeric network (LPTS) using lithiated poly(acrylic acid), silk sericin, and highly branched tannic acid. Covalent cross-linking provides a robust mechanical strength to endure the large stress. The formed multiple hydrogen bonds with bonding energies between 3.46 and 25 kcal mol-1 can effectively dissipate the stress through sequential hydrogen bond disassociation. The multifunctional LPTS binder maintains the integrity of the Si-based electrodes during repeated discharging/charging. Additionally, Li+ can be transferred via a Li-conducting group (-COOLi), thereby enhancing the ionic conductivity of electrodes. Consequently, the Si/LPTS electrode exhibits an improved initial Coulombic efficiency and excellent durability over 400 cycles. Meanwhile, this binder is also suitable for Si-C anodes, enabling stable cycling at a high areal capacity >3.6 mAh cm-2 and delivering 72.2% capacity retention for the LFP||Si-C/LPTS full cell after 200 cycles. This study provides insight into developing efficient Si-based binders that are facile and low-cost for next-generation high-energy-density systems.
ABSTRACT
Aqueous electrolytes have become a research hotspot because of their high safety and low cost, while the inevitable ionization phenomenon of water in aqueous solution leads to the existence of competitive ions (H+) except the active ions. In this article, we take aqueous Na base electrolyte as an example to clear the ion competition behavior by modeling, simulating together with experimental verification. First, the reaction tendency of the two ions (Na+ and H+) is obtained by calculating the Gibbs energy change of the reaction. Furthermore, the properties of electrolytes with different concentrations including transportation are obtained by modeling. After that, relevant experiments are also proceeded to verify the simulation results. Then, the ion competition behavior is analyzed by in situ observation by controlling the constant concentration of Na+: the high concentration of Na+ can reduce the proportion of H+ and reduce the competitiveness of H+; a high concentration of Na+ causes the increased viscosity and reduces the ion diffusion. Based on this, the correlation between ion competitiveness and ion ratio is also confirmed by keeping the concentration of Na+ unchanged and adjusting the concentration of H+ (adjusting pH). The influence of the ion competition phenomenon (Na+ and H+) is the reaction characteristics of the substance itself and the ratio of ion concentration. Finally, the electrochemical performance is further verified in 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDI) symmetric cells and in full-cells with vanadium phosphate sodium (NVP) as the cathode and PTCDI as the anode.
