A study on the interior microstructures of working Sn particle electrode of Li-ion batteries by in situ X-ray transmission microscopy

The interior microstructures of Sn particles developed during electrochemical lithiation/de-lithiation have been revealed by in situ X-ray transmission microscopy (TXM). The Li-alloying particles exhibited the formation of core–shell internal structure along with crack formation within the lithiated zone during the first lithiation. The extent and speed of the expansion process was shown to be a strong function of particle size. Upon completion of the first de-lithiaiton, the particles only partially (～10%) contracted, while re-crystallization of Sn continued to take place within the interior of the particles during a following idle period. The re-crystallization process alleviated the pulverization problem and led to the formation of porous Sn particles, which exhibited remarkably attenuated dimensional variations during subsequent cycles.     

Superabsorbent polymer binder for achieving MnO2 supercapacitors of greatly enhanced capacitance density

One common dilemma encountered in designing a supercapacitor electrode is that the specific capacitance (C_s) of the active material decreases significantly as the active-material loading (mass area^? 1) increases. As a result, the geometric capacitance density (GCD; Farad area^? 1) of the electrode does not scale up linearly but gradually levels off with increasing loading. For MnO₂ supercapacitors, this problem has been solved to a great extent by introducing a superabsorbent polymer (SAP) binder, namely polyacrylic acid (PAA), to form composite particles with MnO₂. Other than acting as a binder to bound together MnO₂ particles, the SAP is believed to facilitate distribution of electrolyte throughout the active layer owing to its electrolyte-absorbing and swelling behaviors. The C_s of MnO₂ remains almost unchanged as the oxide loading varies over a wide range (1.5–6.5 mg cm^? 2) of heavy active-material loading. In addition, putting PAA throughout the entire active layer helps to magnify the specific interaction between PAA and MnO₂ that is known to enhance the capacitance of individual MnO₂ particles. The success in combining both high C_s and high active-material loading results in GCD of ca. 1.8–1.4 F cm^? 2 even under very high current densities (ca. 35–260 mA cm^? 2 or 5–40 A g^? 1-MnO₂).     

Development and characterizations of PVdF-PEMA gel polymer electrolytes

A new class of gel polymer electrolytes comprising the blend of poly(ethyl methacrylate) (PEMA) and poly(vinylidene fluoride), the mixture of ethylene carbonate and propylene carbonate as a plasticizer, and lithium perchlorate (LiClO₄) as a salt was prepared using solvent casting technique. The formation of polymer–salt complexes has been confirmed by XRD analysis. Morphological and thermal studies have been performed using SEM and DMA analyses. A comparative look between PEMA and poly(methyl methacrylate) (PMMA) electrolytes has showed that PEMA electrolytes exhibited better electrochemical performances than PMMA electrolytes, despites its lower conductivity.     

1.2 Volt manganese oxide symmetric supercapacitor

Capacitance fading of MnO₂ supercapacitor electrode under negative polarization below 0.0 V (versus Ag/AgCl/sat. KCl_(aq)) arises from extensive reduction of Mn(IV) to form inactive Mn(II) species, and this has typically limited the operating voltage window of an aqueous symmetric MnO₂ supercapacitor to be no greater than 0.8 V. As this lower potential limit is close to the onset potential of MnO₂-catalyzed oxygen reduction reaction (ORR), the fading problem can be alleviated by effectively passing the accumulated electrons in the oxide electrode to the dissolved oxygen molecules in electrolyte in order to avoid the formation of the surface Mn(II) species. This has been demonstrated by either increasing the dissolved oxygen content or using the Ti(IV)/Ti(III) redox couple in the electrolyte as a charge-transfer mediator to enhance the electrocatalytic activity of MnO₂ for ORR. Therefore, a MnO₂ symmetric supercapacitor showing remarkable cycling stability over an operating voltage window of 1.2 V has been achieved by using Ti(IV)-containing neutral electrolyte (1 M KCl_(aq)).     

Reducing oxy-contaminations for enhanced Li-ion conductivity of halide-based solid electrolyte in water-mediated synthesis

Journal of Solid State Electrochemistry - Liquid-mediated synthesis offers a new approach to producing or applying solid electrolytes (SEs) in all-solid-state Li-ion batteries (ASSLIB). Li-ion...     

High-temperature carbon-coated aluminum current collector for enhanced power performance of LiFePO4 electrode of Li-ion batteries

The charge/discharge capacity and cycle stability at high C-rate of LiFePo₄ (LFPO) electrodes using three types of Al current collectors, including smooth un-etched Al foil, anodization-etched Al foil, and the etched Al foil covered with a conformal C coating grown at 600 °C in CH₄, were investigated. The results unequivocally demonstrate the strong effects exerted by the surface structure and composition of the Al current collectors on the power performance. In particular, the use of the C-coated current collector not only remarkably increases the power-delivering capability, by 3–7-fold based on different comparison criteria, of the LFPO electrode, but also greatly enhances its cycle stability under high C-rate (5C). The rate enhancement exceeds that of a low-temperature organic-bound C-coating reported in the literature. The enhancements are consistent with observed reduction in overall charge-transfer resistance, which can be attributed to the removal of the native insulating oxide surface layer of the current collector and to the improved adhesion at the active layer/current collector interface. This current collector is also applicable to other cathode and anode (e.g., Li₄Ti₅O₁₂) materials of Li-ion batteries for the same beneficial effects.