A comparative investigation of carbon black (Super-P) and vapor-grown carbon fibers (VGCFs) as conductive additives for lithium-ion battery cathodes

To investigate the synergistic effect of different types of conductive additives on the cathode performance of lithium-ion batteries, various types of cathode materials containing different ratios of vapor-grown carbon fibers (VGCFs) and carbon black (Super-P) are investigated. The pillar-like morphology of the VGCFs enabled them to efficiently connect to the active materials and hence, the highest electrical conductivity of LiCoO2 and LiFePO4 (both of which are composed of primary particles) was achieved with the VGCFs. On the other hand, for LiNi0.6Co0.2Mn0.2O2, composed of micro-sized secondary particles embedded with nano-sized primary particles, improved electrical conductivity was achieved with a mixture of VGCF and Super-P via synergistic action

Time-resolved detection of early-arriving ballistic waves in a quasi-diffusive regime

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing AgreementBallistic waves directly carry image information in imaging through a scattering medium, but they are often obscured by much intense multiple-scattered waves. Detecting early arriving photons has been an effective method to extract ballistic waves in the transmission-mode imaging. However, it has been difficult to identify the temporal distribution of ballistic waves relative to the multiple scattering waves in the quasi-diffusive regime. Here, we present a method to separately quantify ballistic and multiple-scattered waves at their corresponding flight times even when multiple scattering is much stronger than the ballistic waves. This is realized by measuring the transmission matrix of an object embedded within scattering medium and comparing the coherent accumulation of ballistic waves with their incoherent addition. To further elucidate the temporal behavior of ballistic waves in quasi-diffusive regime, we analyze the flight time difference between ballistic and multiple-scattered waves and the effect of coherence gating on their relative intensities for the scattering medium of different thicknesses. The presented method to distinctively detect the temporal behavior of ballistic and multiple-scattered waves will lay a foundation to exploit multiple-scattered waves for deep-tissue imaging.11Nsciescopu

Effect of Lithium Substitution Ratio of Polymeric Binders on Interfacial Conduction within All-Solid-State Battery Anodes

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 (DSLi) 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 DSLi 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. © 2023 American Chemical Society.FALS

Journal of Korean nature

A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g^–1), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g^–1 and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g^–1 after 300 cycles at 1.2 A g^–1 and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm^–2, which is a commercially acceptable level, the Si anode could deliver 647 mAh g^–1 until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g^–1

Electrolyte-free graphite electrode with enhanced interfacial conduction using Li+-conductive binder for high-performance all-solid-state batteries

Electrodes supported by conductive binders are expected to outperform ones with inert binders that potentially disturb electronic/ionic contacts at interfaces. Unlike electron-conductive binders, the employment of Li+ conductive binders has attracted relatively little attention due to the liquid electrolyte (LE)-impregnated electrode configuration in the conventional lithium-ion batteries (LIBs). Herein, an all-solid-state electrolyte-free electrode where electrolyte components are completely excluded is introduced as a new tactical electrode construction to evaluate the effectiveness of the Li+-conductive binder on enhancing the interfacial conduction, ultimately leading to high-performance all-solid-state batteries (ASSBs). Conductive lithium carboxymethyl cellulose (Li-CMC) is prepared through an optimized two-step cation-exchange reaction without physical degradation. The electrolyte-free graphite electrode employing Li-CMC as the binder shows strikingly improved areal and volumetric capacity of 1.46 mAh cm(-2) and 490 mAh cm(-3) at a high current rate (1.91 mA cm(-2)) and 60 C which are far superior to those (1.07 mAh cm(-2) and 356.7 mAh cm(-3)) using Na-CMC. Moreover, systematic monitoring of the lithiation dynamics inside the electrolyte-free electrode clarifies that the interfacial Li+ conduction is greatly promoted in the Li-CMC electrode. Complementary analysis from in-depth electrochemical measurements and multiscale simulations verifies that serious internal resistance from impeded interparticle diffusion by inert binders can be substantially mitigated using Li-CMC.N

Direct Correlations of Grain Boundary Potentials to Chemical States and Dielectric Properties of Doped CaCu₃Ti₄O₁₂ Thin Films

Colossal dielectric constant CaCu₃Ti₄O₁₂ has been recognized as one of the rare materials having intrinsic interfacial polarization and thus unusual dielectric characteristics, in which the electrical state of the grain boundary is critical. Here, the direct correlation between the grain boundary potential and relative permittivity is proposed for the CaCu₃Ti₄O₁₂ thin films doped with Zn, Ga, Mn, and Ag as characterized by Kelvin probe force microscopy. The dopants are intended to provide the examples of variable grain boundary potentials that are driven by chemical states including Cu⁺, Ti³⁺, and oxygen vacancy. Grain boundary potential is nearly linearly proportional to the dielectric constant. This effect is attributed to the increased charge accumulation near the grain boundary, depending on the choice of the dopant. As an example, 1 mol % Ag-doped CaCu₃Ti₄O₁₂ thin films demonstrate the best relative permittivity as associated with a higher grain boundary potential of 120.3 mV compared with 82.6 mV for the reference film. The chemical states across grain boundaries were further verified by using spherical aberration-corrected scanning transmission electron microscopy with the simultaneous electron energy loss spectroscopy

Electrolyte-free graphite electrode with enhanced interfacial conduction using Li+-conductive binder for high-performance all-solid-state batteries

Electrodes supported by conductive binders are expected to outperform ones with inert binders that potentially disturb electronic/ionic contacts at interfaces. Unlike electron-conductive binders, the employment of Li+-conductive binders has attracted relatively little attention due to the liquid electrolyte (LE)-impregnated electrode configuration in the conventional lithium-ion batteries (LIBs). Herein, an all-solid-state electrolyte-free electrode where electrolyte components are completely excluded is introduced as a new tactical electrode construction to evaluate the effectiveness of the Li+-conductive binder on enhancing the interfacial conduction, ultimately leading to high-performance all-solid-state batteries (ASSBs). Conductive lithium carboxymethyl cellulose (Li-CMC) is prepared through an optimized two-step cation-exchange reaction without physical degradation. The electrolyte-free graphite electrode employing Li-CMC as the binder shows strikingly improved areal and volumetric capacity of 1.46 mAh cm???2 and 490 mAh cm???3 at a high current rate (1.91 mA cm???2) and 60 ??C which are far superior to those (1.07 mAh cm???2 and 356.7 mAh cm???3) using Na-CMC. Moreover, systematic monitoring of the lithiation dynamics inside the electrolyte-free electrode clarifies that the interfacial Li+ conduction is greatly promoted in the Li-CMC electrode. Complementary analysis from in-depth electrochemical measurements and multiscale simulations verifies that serious internal resistance from impeded interparticle diffusion by inert binders can be substantially mitigated using Li-CMC

Thin, Highly Ionic Conductive, and Mechanically Robust Frame-Based Solid Electrolyte Membrane for All-Solid-State Li Batteries

A thin but robust solid electrolyte layer is crucial for realizing the theoretical energy density of all-solid-state batteries (ASSBs) beyond state-of-the-art Li-ion batteries (LIBs). This study proposes a simple but practical strategy for fabricating thin solid electrolyte membranes using 5-µm perforated polyethylene separators with 35% open areas as the supporting component, which ensures mechanical robustness for commercial-level cell assembly. The thickness of this frame-based solid electrolyte (f-SE) membrane can be reduced to ≈45µm, even after coating the Li6PS5Cl (LPSCl) solid electrolyte composite. Despite a slightly lower ionic conductivity compared to that of thick LPSCl pellets, the f-SE membranes show high conductance and low overpotential in Li||Li symmetric cells. Their incorporation into LiNi0.7Co0.15Mn0.15O2 full cells increases the reversible capacity and rate capability compared to those of cells with conventional LPSCl pellets. The f-SE membrane cells exhibit excellent cycling stability over 250 cycles, while maintaining high-capacity retention and Coulombic efficiency. Notably, the f-SE membranes significantly increase the energy density of ASSBs (314Whkg−1), exceeding the values reported for sulfide-based cells. These results highlight the crucial role of f-SE membranes in improving the mechanical properties and energy density of ASSBs, thereby contributing to the development of next-generation Li battery technologies. © 2023 Wiley-VCH GmbH.FALS