Thermal Runaway Behavior of Li6PS5Cl Solid Electrolytes for LiNi0.8Co0.1Mn0.1O2 and LiFePO4 in All-Solid-State Batteries

All-solid-state batteries (ASSBs) have received much attention because of their high energy density and safety. However, the safety of argyrodite-type Li6PS5Cl (LPSCl)-based ASSBs is still not assured because their thermal stability has been assessed under selected mild conditions. Herein, we introduce the poor thermal stability of LPSCl with Ni-rich layered oxide cathode materials as the trigger of thermal runaway. The charged composite cathode pellets containing Li1-xNi0.8Co0.1Mn0.1O2 and LPSCl are explosively burned at 150 degrees C even in Ar. Moreover, the mechanical abuse gives rise to violent burning at room temperature. This is due to vigorous exothermic chemical reactions between delithiated Li1-xNi0.8Co0.1Mn0.1O2 and LPSCl. However, LPSCl with LiFePO4 exhibits excellent thermal stability, such as no violent exothermic reactions even at 350 degrees C. This is because LPSCl is metastable with delithiated Li1-xFePO4. Moreover, LiFePO4 shows excellent electrochemical performance, such as a high reversible capacity of 141 mAh g-1 and stable capacity retention over 1000 cycles, despite the fact that LiFePO4 is known to be poorly electrochemically active for ASSBs. These findings provide fundamental insights to improve the thermal stability and electrochemical performance of LPSCl-based ASSBs.N

Residual Li Compounds-Selective Washing Process for Ni-Rich Layered Oxide Cathode Materials for Li-Ion Batteries

The industrial manufacturing process for Ni-rich layered oxides for Li-ion batteries includes a washing step to remove residual Li compounds, such as LiOH and Li2CO3, from the oxide surface. However, Ni-rich layered oxides are deformed during a conventional water-based washing process, leading to the degradation of the oxide surface. In this regard, a significant challenge for Ni-rich layered oxides is to remove residual Li compounds without surface damage during a washing process. Herein, the residual Li compounds-selective washing process is introduced as a promising strategy for LiNi0.945Co0.04Al0.015O2 to suppress the degradation of the oxide surface during washing. The selectively hydrophobic LiNi0.945Co0.04Al0.015O2 powders are obtained through selective coating only on the LiNi0.945Co0.04Al0.015O2 surface with hydrophobic polydimethylsiloxane, leaving residual Li compounds uncoated. For this reason, the oxide surface is hydrophobic, whereas the residual Li compounds surface is hydrophilic. As a result, only residual Li compounds are selectively exposed to water and removed during washing, mitigating contact between the oxide surface and water. Eventually, this method suppresses the degradation of the LiNi0.945Co0.04Al0.015O2 surface during washing, resulting in the improved electrochemical performance compared to LiNi0.945Co0.04Al0.015O2 obtained through a conventional washing technique.

Computational and Histological Analyses for Investigating Mechanical Interaction of Thermally Drawn Fiber Implants with Brain Tissue

The development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness

Direct observation of the in-plane crack formation of O3-Na0.8Mg0.2Fe0.4Mn0.4O2 due to oxygen gas evolution for Na-ion batteries

Crack formation is considered one of the significant failure modes of layered oxide cathode materials for Na-ion batteries because particle cracks accelerate electrolyte decomposition, transition metal dissolution, and electrical contact loss. However, the crack formation mechanism of layered sodium transition metal oxides has not been fully understood yet. Herein, the in-plane crack formation mechanism of O3-type Na0.8Mg0.2Fe0.4Mn0.4O2 is demonstrated in terms of oxygen gas evolution due to air-exposure using in situ mass spectrometry and various atomic-scale analyses. When Na0.8Mg0.2Fe0.4Mn0.4O2 is exposed to air, Na+ ions are unevenly deintercalated in a form of stripe pattern along the in-plane direction. The deintercalation of Na+ ions gives rise to phase transition from the layered structure to the disordered structure, including spinel-like and rock salt-like structures, resulting in forming the nanoscale vertical heterostructure of alternating layered and disordered phases along the out-of-plane direction. The formation of the disordered structure is accompanied by oxygen gas evolution. As a result, cracks occur along the in-plane direction of Na0.8Mg0.2Fe0.4Mn0.4O2 because of the internal gas pressure due to oxygen gas evolution. Moreover, air-stable surface-modified Na0.8Mg0.2Fe0.4Mn0.4O2 is introduced to suppress crack formation, leading to excellent electrochemical performance, such as stable capacity retention over 200 cycles.

Ligand Coupling and Decoupling Modulates Stem Cell Fate

In natural microenvironment, various proteins containing adhesive ligands in fibrous and non-fibrous structures dynamically couple and decouple to regulate stem cell fate. Herein, materials presenting movably couplable ligands are developed by grafting liganded gold nanoparticles (AuNPs) to a substrate followed by flexibly grafting liganded movable linear nanomaterials (MLNs) to the substrate via a long bendable linker, thereby creating a space between the MLNs and the AuNPs in the decoupled state. Magnetic control of the MLNs decreases this space via the bending of the linker to couple the MLNs to the AuNPs. Remote control of ligand coupling stimulates integrin recruitment to the coupled ligands, thereby non-toxically facilitating the focal adhesion, mechanosensing, and potential differentiation of stem cells, which is suppressed by ligand decoupling. Versatile tuning of size, aspect ratio, distributions, and ligands of the MLNs can help to decipher dynamic ligand-coupling-dependent stem cell fate to advance regenerative therapies.11Nsciescopu

Modulation of Macrophages by In Situ Ligand Bridging

Extracellular matrix (ECM) proteins containing cell-attachable Arg-Gly-Asp (RGD) sequences exhibit variable bridging and non-bridging in fibronectin-collagen and laminin-collagen complexes that can regulate inflammation, tissue repair, and wound healing. In this study, linking molecule-mediated conjugation of 1D magnetic nanocylinders (MNCs) to material surfaces pre-decorated with gold nanospheres (GNSs) is performed, thereby yielding RGD-coated MNCs (RGD-MNCs) over RGD-coated GNSs (RGD-GNSs) in a non-bridging state. The RGD-MNCs are drawn closer to the RGD-GNSs via magnetic field-mediated compression of the linking molecules to establish the bridging between them. Relative proportion of the RGD-MNCs to the RGD-GNSs is optimized to yield effective remote stimulation of integrin binding to variably bridged RGDs similar to that of invariably bridged RGDs used as a control group. Remote manipulation of the RGD bridging facilitates the attachment structure assembly of macrophages that leads to pro-healing/anti-inflammatory phenotype acquisition. In contrast, the non-bridged RGDs inhibited macrophage attachment that acquired pro-inflammatory phenotypes. The use of various nanomaterials in constructing heterogeneous RGD-coated materials can further offer various modes in remote switching of RGD bridging and non-bridging to understand dynamic integrin-mediated modulation of macrophages that regulate immunomodulatory responses, such as foreign body responses, tissue repair, and wound healing

Photoswitchable Microgels for Dynamic Macrophage Modulation

Dynamic manipulation of supramolecular self-assembled structures is achieved irreversibly or under non-physiological conditions, thereby limiting their biomedical, environmental, and catalysis applicability. In this study, microgels composed of azobenzene derivatives stacked via pi-cation and pi-pi interactions are developed that are electrostatically stabilized with Arg-Gly-Asp (RGD)-bearing anionic polymers. Lateral swelling of RGD-bearing microgels occurs via cis-azobenzene formation mediated by near-infrared-light-upconverted ultraviolet light, which disrupts intermolecular interactions on the visible-light-absorbing upconversion-nanoparticle-coated materials. Real-time imaging and molecular dynamics simulations demonstrate the deswelling of RGD-bearing microgels via visible-light-mediated trans-azobenzene formation. Near-infrared light can induce in situ swelling of RGD-bearing microgels to increase RGD availability and trigger release of loaded interleukin-4, which facilitates the adhesion structure assembly linked with pro-regenerative polarization of host macrophages. In contrast, visible light can induce deswelling of RGD-bearing microgels to decrease RGD availability that suppresses macrophage adhesion that yields pro-inflammatory polarization. These microgels exhibit high stability and non-toxicity. Versatile use of ligands and protein delivery can offer cytocompatible and photoswitchable manipulability of diverse host cells