Jae Hong Choi

The growing demand for clean energy technologies has significantly increased interest in lithium-ion batteries (LIBs) for applications in electric vehicle and grid-level energy storage. High-nickel layered oxide cathode materials are considered one of the strong candidates due to their high specific capacity, yet their practical utilization is restricted by challenges related to complicated wet synthesis methods, scalability, and low performance, particularly in the case of single-crystal structures. Conventional synthesis of high-nickel single-crystal materials generally involves a two-step coprecipitation route that requires extended precursor preparation before lithiation and requires careful regulation of multiple synthesis parameters. In this study, we utilize a simplified one-step all-dry phase synthesis strategy for a high-nickel single-crystal LiNi0.9Co0.05Mn0.05O2 (NCM911) cathode material using oxide precursors. The process solely relies on simple mechanical/hand mixing, eliminating the need for high-energy milling, solvent, acids, and washing steps that may negatively affect the structural stability. By careful controlling/tuning the lithium stoichiometry and sintering temperature, single-crystal NCM911 cathode materials with controlled size and morphology were successfully synthesized. In this work, the lithium/transition metal (Li/TM) ratio and sintering temperature condition were controlled/tuned at 1.2:1 and 850 °C, respectively, under an O2 atmosphere in order to achieve good electrochemical performance. As a result, the best performing electrode exhibits an initial discharge capacity of 207.4 mAh g−1, achieving an initial columbic efficiency of 88.4%. This approach can effectively reduce the synthesis complexity, processing time, environmental degradation, and overall cost while maintaining compatibility with current manufacturing technologies, providing a practical pathway for the scalable one-step all-dry process synthesis of high-nickel single-crystal cathode materials.

The development of high-energy-density lithium-ion batteries (LIBs) is crucial to meet the increasing demands of electric vehicles (EVs), hybrid electric vehicles (HEVs), portable electronics, and large-scale energy storage systems. In this context, dry electrode fabrication has emerged as a sustainable and cost-effective alternative to conventional slurry-based processing, particularly for high-loading thick electrodes. However, intensive calendaring required in dry thick electrode processing induces significant mechanical stress, often leading to particle cracking in nickel-rich layered oxide cathodes and consequent electrochemical degradation. Herein, we systematically investigated the mechanical robustness and electrochemical performance of single-crystal S-LiNi0.8Co0.1Mn0.1O2 (S-NCM811) cathodes fabricated via a dry electrode route. The single-crystal S-NCM811 demonstrates superior structural integrity with significantly reduced particle cracking after calendaring, as confirmed by SEM analysis. Electrochemical evaluations reveal enhanced lithium-ion transport kinetics, lower charge-transfer resistance, and improved porosity in S-NCM811 compared to its polycrystalline counterpart. As a result, the S-NCM811 dry thick electrode achieves a high-capacity retention of 91.5% at 0.5 C after 50 cycles at a high mass loading of ∼35 mg cm–2, as compared to P-NCM811, which retained only 63.4% of its initial capacity after subsequent cycles. This work highlights the critical role of crystal morphology in mitigating mechanical degradation during dry processing and provides valuable insights into the design of robust nickel-rich cathodes for next-generation high-energy-density LIBs.

Lithium-ion batteries serve as a key technology, establishing the advancement of energy storage devices and playing a vital role in the global shift toward sustainable and green energy. However, the growing demand for high capacity nickel (Ni)-rich lithium-ion batteries accelerates the optimization of their energy density. A high-mass loading electrode design is a promising strategy for enhancing the energy density of LIBs, enabling the improved performance for commercial applications. The factors that limit the rate capability of the high-mass loading electrode are associated with the underutilization of active materials and increased polarization, which can be further attributed to slow electronic/ionic transport within the electrode. In this work, the conductive networks and porous characteristics of the Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode electrode is preciously tailored through the incorporation of multidimensional carbon conductive additives, facilitating enhanced electron transport and optimized porosity enhancing lithium-ion diffusion within the high-mass loading electrode. As a result, the NCM811 cathode electrode with dual-multidimensional conductive additives, such as carbon black and carbon nanofiber (CB + CNF), exhibits an outstanding performance, achieving a capacity retention of 94.8% over 100 cycles at 1 C. It is also observed that long-structured CNFs contributes significantly to the formation of efficient conductive networks in a high-mass loading thick electrode (∼23 mg cm^-2) exhibiting excellent performance at 0.2 C. The simple yet fundamental principle uncovered through this work demonstrates that the integration of the dual-carbon system synergistically enhances the conductive networks and optimizes electrode porosity. This microstructural optimization effectively reduces Ohmic contact resistance, contributing to a significantly enhanced electrochemical performance.

Interest in using thick LiFePO₄ cathodes to enhance lithium-ion battery energy density has recently been growing. To obtain thick cathodes with superior electrical conductivity throughout their depth, it is crucial to substitute conventional zero-dimensional conductive agents with one-dimensional carbon nanotubes (CNTs). Nevertheless, the inherent properties of CNT, including their high aspect ratio and strong van der Waals interaction, hinder uniform dispersion, causing poor performance in thick electrodes. In this work, we adopted an electrostatic energy-driven dispersion (EED) method to achieve a homogeneous distribution of multiwalled carbon nanotubes (MWCNTs) with LiFePO₄ for thick cathodes. The EED process, guided by the charge residue model and ion evaporation model theories, facilitated the formation of a well-distributed LiFePO₄-MWCNT composite. This method yielded e-LiFePO₄/MWCNT composites with consistent morphology even at a high MWCNT concentration (5 wt %), as verified by cross-sectional scanning electron microscopy and a microcomputed tomography scan. The e-LiFePO₄/MWCNT cathode exhibited reduced overpotential during the Li-ion redox process, along with enhanced areal capacity and capacity retention (7.27 mAh cm^-2 at 0.3 C and 80.74% after 90 cycles), outperforming the conventional mixing-only method. These results underline the importance of prioritizing the uniform distribution of active materials and conductive agents in future thick electrode research.

All-solid-state lithium batteries, including sulfide electrolytes and nickel-rich layered oxide cathode materials, promise safer electrochemical energy storage with high gravimetric and volumetric densities. However, the poor electrical conductivity of the active material results in the requirement for additional conducive additives, which tend to react negatively with the sulfide electrolyte. The fundamental scientific principle uncovered through this work is simple and suggests that the electrical network benefits associated with the introduction of short-length carbons will eventually be overpowered by the increase in bulk resistance associated with their instability in the sulfide electrolyte. However, applying just the right amount of short carbon fibres minimizes degradation of the sulfide solid electrolyte and maximizes the electron movement. Therefore, we propose the application of a low-weight-percent carbon nanotubes (CNTs) coating on the nickel-rich cathode LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) along with large-aspect-ratio carbon nanofibers (CNFs) as the primary conductive additive. When only 0.3 wt % CNTs was utilized with 4.7 wt % CNFs, an initial Coulombic efficiency of 83.55% at 0.05C and a notably excellent capacity retention of 90.1% over 50 cycles at 0.5C were achieved along with a low ionic resistance. This work helps to confirm the validity of applying short carbon pathways in sulfide-electrolyte-based cathode composites and proposes their combination with a larger primary carbon additive as a solution to the ongoing all-solid-state battery rate and instability issues.

All-solid-state lithium-ion batteries (ASSLBs) have recently received significant attention due to their exceptional energy/power densities, inherent safety, and long-term electrochemical stability. However, to achieve energy- and power-dense ASSLBs, the cathode composite electrodes require optimum ionic and electrical pathways and hence the development of electrode designs that facilitate such requirements is necessary. Among the various available conductive materials, carbon black (CB) is typically considered as a suitable carbon additive for enhancing electrode conductivity due to its affordable price and electrical-network-enhancing properties. In this study, we examined the effect of different weight percentages (wt%) of nano-sized CB as a conductive additive within a cathode composite made up of Ni-rich cathode material (LiNi_0.8Co_0.1Mn_0.1O₂) and solid electrolyte (Li₆PS₅Cl). Composites including 3 wt%, 5 wt%, and 7 wt% CB were produced, achieving capacity retentions of 66.1%, 65.4%, and 44.6% over 50 cycles at 0.5 C. Despite an increase in electrical conductivity of the 7 wt% CB sample, a significantly lower capacity retention was observed. This was attributed to the increased resistance at the solid electrolyte/cathode material interface, resulting from the presence of excessive CB. This study confirms that an excessive amount of nano-sized conductive material can affect the interfacial resistance between the solid electrolyte and the cathode active material, which is ultimately more important to the electrochemical performance than the electrical pathways.

Sulfide electrolyte all-solid-state lithium-ion batteries (ASSLBs) that have inherently nonflammable properties have improved greatly over the past decade. However, determining both the stable and functional electrode components to pair with these solid electrolytes requires significant investigation. Solid electrolyte comprises 20–40% of the composite cathode electrode, which improves the ionic conductivity. However, this results in thick electrolyte that blocks the electron pathways in the electrode, significantly lowering the electrochemical performance. The application of conductive carbon material is required to overcome this issue, and, hence, determining the carbon properties that result in the most stable performance in the sulfide solid electrolyte is vital. This study analyzes the effect of the cathode conductive additive’s morphology on the electrochemical performance of sulfide electrolyte-based ASSLBs. Carbon black (CB) and carbon nanotubes (CNTs), which provide electron pathways at the nanoscale and sub-micron scale, and carbon nanofiber (CNF), which provides electron pathways at the tens-of-microns scale, are all tested individually as potential conductive additives. When the CNF, with its high crystallinity, is used as a conductive material, the electrochemical performance shows an excellent initial discharge capacity of 191.78 mAh/g and a 50-cycle capacity retention of 83.9%. Conversely, the CB and the CNTs, with their shorter pathways and significantly increased surface area, show a relatively low electrochemical performance. By using the CNF to provide excellent electrical conductivity to the electrode, the polarization is suppressed. Furthermore, the interfacial impedance across the charge transfer region is also reduced over 50 cycles compared with the CB and CNT composite cells. These findings stringently analyze and emphasize the importance of the morphology of the carbon conductive additives in the ASSLB cathode electrodes, with improvements in the electrochemical performance being realized through the application of long-form two-dimensional crystalline CNFs.