On-Site Cross-Linking of Polyacrylamide to Efficiently Bind the Silicon Anode of Lithium-Ion Batteries.

Silicon anode suffers from rapid capacity decay because of its irreversible volume changes during charging and discharging. As one of the important components of the electrode structure, the binder plays an irreplaceable role in buffering the volume changes of the silicon anode and ensuring close contact between various components of the electrode. Traditional PVDF binder is based on weak van der Waals forces and cannot effectively buffer the stress coming from silicon volume expansion, resulting in rapid decay of silicon anode capacity. In addition, most natural polysaccharide binders with a single force face the same problem due to poor toughness. Therefore, it is extremely important to develop a binder with good force and toughness between the silicon particles. Herein, polyacrylamide (PAM) polymer chains that are premixed homogeneously with various components are cross-linked on-site on the current collector via the condensation reaction with citric acid, forming a polar three-dimensional (3D) network with improved tensile properties and adhesion for both silicon particles and current collector. The silicon anode with the cross-linked PAM binder exhibits higher reversible capacity and enhanced long-term cycling stability; the capacity remains at 1280 mA h g-1 after 600 cycles at 2.1 A g-1 and 770.9 mA h g-1 after being subjected to 700 cycles at 4.2 A g-1. It also exhibits excellent cycle stability in silicon-carbon composite materials. This study provides a cost-effective binder engineering strategy, which significantly enhances the long-term cycle performance and stability of silicon anodes, paving the way for large-scale practical applications.

Formulating a New Electrolyte: Synergy between Low-Polar and Non-polar Solvents in Tailoring the Solid Electrolyte Interface for the Silicon Anode.

Currently, lithium-ion batteries (LIBs) are assembled with polar electrolytes; thus, resulting SEI layers are dominated with organics. Herein, a low-polarity electrolyte is formulated with a low-polarity solvent (tetraethyl silicate, TEOS) and a non-polar inert shielding co-solvent (cyclohexane, CYH); solvation behaviors of lithium salt are investigated. The use of such a low-polarity solvent is found to improve the fraction of anions in the solvation sheath of Li+, and the presence of the non-polar co-solvent further shields the reductive decomposition of the solvent on the anode. The resulting SEI layer is relatively rich in LiF and has a 3D cross-linked Si-O network as a skeleton from the decomposition of TEOS molecules, which is more robust to tolerate the damage from the volume expansion of silicon. A Si-nanoparticle-based anode in such a low-polarity electrolyte delivers a capacity as high as 1491 mAh g-1 after 200 cycles, outperforming those in the commercial polar electrolytes.

Cyclorhizapuana (Apiaceae), a new species from Sichuan, China.

A new species, Cyclorhizapuana J. Zhou & Z.W. Liu (Apiaceae) from Sichuan Province of China, is described and illustrated here. Morphological comparisons with congeneric species revealed that it is distinguished by its slender habit, sparse annular scars, 4-pinnatisect leaf blade with ultimate segments linear (2-4×0.5-1 mm), subequal rays, oblong fruits with slightly thickened ribs, obconic stylopodium and slightly concave seed face. A molecular analysis based on nuclear ribosomal DNA internal transcribed spacer (ITS) sequences indicated that C.puana is genetically distinct from the other two species of the genus. A distribution map, as well as an updated key, are provided for the species of Cyclorhiza.