Maenghyo Cho

All-solid-state battery (ASB) systems are considered a promising energy-storage system to advance the next generation of electronic devices. However, it is known that LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) as an electrode provokes a contact-loss problem at the interface with Li₁₀GeP₂S₁₂ (LGPS) as the solid electrolyte (SE). Also, the fundamental mechanism of contact loss has not been comprehensively described yet. For these reasons, we designed an electro-chemo-mechanical multi-scale and multi-physics model initially to examine the mechanism of contact loss. The electrochemical and mechanical properties of NCM811 and LGPS were calculated at the nanoscale. Then, the complex phenomenon of contact loss considering the electrochemical and mechanical physics was analyzed at the micro/macro scale together with the calculated properties. Using designed methodology bridging the nano scale and micro/macro scale with combined physics, we confirmed that the contraction of NCM811 during the charge directly leads to a swelling of LGPS. The compliant LGPS instantly absorbs the displacement fields from NCM811 and then undergoes crack generation at the interface. Contact loss limits the flow of Li ions and causes a short circuit. In addition, we confirmed that applying a polymer filler with hyperelasticity at the interface and external pressure to the cell can be considered as possible solutions to relieve the contact loss, and both remedies could effectively suppress the contact loss. The introduction of both remedies at the same time also showed synergetic effects, whereby applying a thin filler with external pressure could suppress contact loss as much as applying a thick filler.

The paper-folding mechanism has been widely adopted in building of reconfigurable macroscale systems because of its unique capabilities and advantages in programming variable shapes and stiffness into a structure^1,2,3,4,5. However, it has barely been exploited in the construction of molecular-level systems owing to the lack of a suitable design principle, even though various dynamic structures based on DNA self-assembly^6,7,8,9 have been developed^{10,11,12,13,14,15,16,17,18,19,20,21,22,23}. Here we propose a method to harness the paper-folding mechanism to create reconfigurable DNA origami structures. The main idea is to build a reference, planar wireframe structure²⁴ whose edges follow a crease pattern in paper folding so that it can be folded into various target shapes. We realized several paper-like folding and unfolding patterns using DNA strand displacement²⁵ with high yield. Orthogonal folding, repeatable folding and unfolding, folding-based microRNA detection and fluorescence signal control were demonstrated. Stimuli-responsive folding and unfolding triggered by pH or light-source change were also possible. Moreover, by employing hierarchical assembly²⁶ we could expand the design space and complexity of the paper-folding mechanism in a highly programmable manner. Because of its high programmability and scalability, we expect that the proposed paper-folding-based reconfiguration method will advance the development of complex molecular systems.

Problematic issues with electrically inert binders have been less serious in the conventional lithium-ion batteries by virtue of permeable liquid electrolytes (LEs) for ionic connection and/or carbonaceous additives for electronic connection in the electrodes. Contrary to electron-conductive binders used to maximize an active loading level, the development of ion-conductive binders has been lacking owing to the LE-filled electrode configuration. Herein, we represent a tactical strategy for improving the interfacial Li⁺ conduction in all-solid-state electrolyte-free graphite (EFG) electrodes where the solid electrolytes are entirely excluded, using lithium-substitution-modulated (LSM) binders. Finely tuning a lithium substitution ratio, a conductive LSM-carboxymethyl cellulose (CMC) binder is prepared from a controlled direct Na⁺/Li⁺ exchange reaction without a hazardous acid involvement. The EFG electrode employing LSM with a maximum degree of substitution of lithium (DS_Li) of ∼68% in our study shows a considerably higher rate capability of 1.05 mA h cm^-2 at 1 C and a capacity retention of ∼61.9% after 200 cycles at 0.5 C than those using sodium-CMC (Na-CMC) (0.78 mA h cm^-2, ∼49.5%) and LSM with ∼35% lithium substitution (0.93 mA h cm^-2, ∼55.4%). More importantly, the correlation between the phase transition near the bottom region of the EFG electrode and the state of charge (SOC) is systematically investigated, clarifying that the improvement of the interfacial conduction is proportional to the DS_Li of the CMC binders. Theoretical calculations combined with experimental results further verify that creating the continuous interface through abundant pathways for mobile ions using the Li⁺-conductive binder is the enhancement mechanism of the interfacial conduction in the EFG electrode, mitigating serious charge transfer resistance.

Solid electrolytes (SEs) are critical for next-generation all solid-state batteries with high energy density and fire safety. However, recent studies observed that the Li metallic phase nucleates at the electrode interfaces as well as the interfaces between crystalline grains of SEs. Many studies have revealed the origins and control methods for Li metallic phase formation at the anode interface, but a thorough understanding of metallic Li formation at intergranular regions in SEs has not been developed yet. Through systematic DFT simulations, we present a thorough atomistic study that reveals the impact of intergranular regions on Li-metallic phase formation in SEs using the perovskite Li_3xLa_(2/3)−x□_(1/3)−2xTiO₃ (0 < x < 0.167) (LLTO) as a model SE. We investigated the three representative model structures for intergranular regions, which are experimentally observed with various microstructure configurations: (i) stoichiometric grain boundary (GB), (ii) A-site deficient GB, and (iii) intergranular pore space. In the stoichiometric GB, the GB region has an electron insulating feature regardless of A-site compositions (0 < x < 0.167). In the A-site deficient GB, however, the GB region has electronic conductivity, but it has a high repulsive force against Li-ions moving into the GB region. However, in the intergranular pore structure, Li-ions prefer to move with a neutral charge state into the pore space which shows a p-type conductive property. Accordingly, Li metallic phase nucleation starts in the intergranular pore space of the SE. These results elucidate the critical role of pore space in SEs for Li metallic phase nucleation and provide an insight into the design of Li metallic phase-free SEs and further studies on SE materials.

Azobenzene-incorporated liquid crystalline polymer (azo-LCP), which undergo property change and deformation upon Ultra violet and visible light stimulation, are promising materials in various fields. This study investigated the effect of azobenzene concentration on photosoftening based on the photoisomerization of an azo-LCP. The experimental results confirmed that as the azobenzene concentration increased, the order parameter decreased and mechanical properties deteriorated. Photoisomerization and photosoftening was also conducted on an azo-LCP unit cell constructed by molecular dynamics simulation. The simulation results showed that changes in the order parameter, length contraction and elastic modulus due to the photosoftening, in alignment with the experimental results.

Deformations triggered by body heat are desirable in the context of shape‐morphing applications because, under the majority of circumstances, the human body maintains a higher temperature than that of its surroundings. However, at present, this bioenergy‐triggered action is primarily limited to soft polymeric networks. Thus, herein, the programming of body temperature‐triggered deformations into rigid azobenzene‐containing liquid crystalline polymers (azo‐LCPs) with a glass‐transition temperature of 100 °C is demonstrated. To achieve this, a mechano‐assisted photo‐programming strategy is used to create a metastable state with room‐temperature stable residual stress, which is induced by the isomerization of azobenzene. The programmed rigid azo‐LCP can undergo large‐amplitude body temperature‐triggered shape changes within minutes and can be regenerated without any performance degradation. By changing the programming photomasks and irradiation conditions employed, various 2D to 3D shape‐morphing architectures, including folded clips, inch‐worm structures, spiral structures, and snap‐through motions are achieved. When programmed with polarized light, the proposed strategy results in domain‐selective activation, generating designed characteristics in multi‐domain azo‐LCPs. The reported strategy is therefore expected to broaden the applications of azo‐LCPs in the fields of biomedical and flexible microelectronic devices.