Yong Min Lee

The commercialization of Li metal electrodes is a long-standing objective in the battery community. To accomplish this goal, the formation of Li dendrites and mossy Li deposition, which cause poor cycle performance and safety issues, must be resolved. In addition, it is necessary to develop wide and thin Li metal anodes to increase not only the energy density, but also the design freedom of large-scale Li-metal-based batteries. We solved both issues by developing a novel approach involving the application of calendared stabilized Li metal powder (LiMP) electrodes as anodes. In this study, we fabricated a 21.5 cm wide and 40 μm thick compressed LiMP electrode and investigated the correlation between the compression level and electrochemical performance. A high level of compression (40% compression) physically activated the LiMP surface to suppress the dendritic and mossy Li metal formation at high current densities. Furthermore, as a result of the LiMP self-healing because of electrochemical activation, the 40% compressed LiMP electrode exhibited an excellent cycle performance (reaching 90% of the initial discharge capacity after the 360th cycle), which was improved by more than a factor of 2 compared to that of a flat Li metal foil with the same thickness (90% of the initial discharge capacity after the 150th cycle).

Herein, we improved the performance of Si/graphite (Si/C) composite anodes by introducing a highly adhesive co-polyimide (P84) binder and investigated the relationship between their electrochemical and adhesion properties using the 90° peel test and a surface and interfacial cutting analysis system. Compared to those of conventional poly(vinylidene fluoride) (PVdF)-based electrodes, the cycling performance and rate capability of P84-based Si/C anodes were improved by 47.0% (372 vs 547 mAh g^–1 after 100 cycles at a 60 mA g^–1 discharge condition) and 33.4% (359 vs 479 mAh g^–1 after 70 cycles at a 3.0 A g^–1 discharge condition), respectively. Importantly, the P84-based electrodes exhibited less pronounced morphological changes and a smaller total cell resistance after cycling than the PVdF-based ones, also showing better interlayer adhesion (F_mid) and interfacial adhesion to Cu current collectors (F_inter).

Exposure of battery tabs to humid air triggers self-discharge of batteries because of the induction effect of polar water molecules.

A new Cu current collector was prepared by introducing a mussel-inspired polydopamine coating onto a Cu foil surface to improve the electrochemical performance of a Si electrode. The polydopamine coating covalently bonded the polymeric binder (with hydroxyl functional groups) via a condensation reaction. The coating improved the adhesion strength between the Si composite electrode and the Cu current collector (245.5 N m⁻¹, 297.5 N m⁻¹, and 353.2 N m⁻¹ for the Si electrodes based on bare Cu, polydopamine-treated Cu without thermal treatment, and polydopamine-treated Cu with thermal treatment, respectively). We demonstrate that the detachment between the Si composite electrode and the current collector plays an important role in determining the electrochemical performance of the Si electrode. The cycle life and rate capability of the Si electrode improved when the polydopamine surface-treated Cu current collector was used (963.9 mAh g⁻¹, 1361.1 mAh g⁻¹, and 1590.0 mAh g⁻¹ for the Si electrodes based on bare Cu, polydopamine-treated Cu without thermal treatment, and polydopamine-treated Cu with thermal treatment, respectively, at C/2 after 500 cycles).

Dopamine, which can be electrochemically oxidized to polydopamine on cathode surface, was introduced as an electrolyte additive for high-voltage lithium-ion batteries (LIBs). The addition of 0.1 wt % dopamine to the electrolyte led to the formation of a polydopamine-containing layer on the cathode, thereby resulting in suppression of the oxidative decomposition of the electrolyte during high-voltage operation (up to 4.5 V) of a LiNi_1/3Co_1/3Mn_1/3O₂/artificial graphite cell. The addition of dopamine to the electrolyte improved the capacity retention of the cell from 136 to 147 mAh g^–1 after 100 cycles at a rate of 1 C and a cutoff voltage of 4.5 V, while the cycle performance and rate capability with a cutoff voltage of 4.3 V were comparable to those of the cell without dopamine. Further evidence of the positive impact of dopamine on high-voltage LIBs was the lower DC-IRs and AC impedances, as well as the retention of the cathode morphology even after operation at 4.5 V.

The study has developed a facile polydopamine (PD) surface coating method for a typical conductive additive, Super‐P. This method is efficient, economical, and environmentally friendly, and it can be used for the mass production of Super‐P. PD treatment converts the hydrophobic surfaces of Super‐P into hydrophilic surfaces, facilitating slurry preparation, and slurry coating for the fabrication of Si‐based electrodes. Furthermore, the unique adhesion properties of PD and its ability to form a cross‐linking network with polymeric binders such as poly(acrylic acid) improve the cycle performance of Si anodes containing PD‐treated Super‐P (1395.1 mAh g^–1 after 1000 cycles, and 1200 mA g^–1 for charging and discharging processes). A postmortem scanning electron microscopy study reveals that PD‐treated Super‐P efficiently reduces the mechanical stress of Si anodes caused by large volumetric changes that occur during lithiation and delithiation.

Repressing uncontrolled lithium (Li) dendrite growth is the top priority for enabling the reliable use of Li metal secondary batteries. On the other hand, the technique controlling the metal plating behavior during metal plating indeed has been considered very difficult to achieve. For instance, how can one plate metal ions on the favored selected region during plating? The present study describes how to achieve this goal, i.e., dendrite‐free Li deposition, by mechanical surface modification using a simple stamping technique, where finite‐element method simulation using COMSOL Multiphysics was used to design the micro‐patterns of the stamp. After stamping, the transferred micro‐patterns on Li metal anodes suppress dendrite growth during repeated Li deposition/stripping processes and exhibit improved long‐term cycling stability of Li metal anodes. During the repeated Li plating processes, the pattern holes are filled by the liquid‐like and/or granular forms of Li metal without resulting Li dendrite growth. These holes are then reversibly drained during the Li stripping process, reverting to their original dimension. This study investigated the correlation of this unique Li plating/stripping behavior as a function of the current density.

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 LiNi_0.6Co_0.2Mn_0.2O₂, 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.

Computational Simulation on Power Prediction of Lithium Secondary Batteries by using Pulse-based Measurement Methods Energy Storage System;Lithium Secondary Battery;Computer Modeling;Computational Simulation;Power; Energy storage systems (ESSs) have been utilized widely in the world to optimize the power operation system and to improve the power quality. As lithium secondary batteries are the main power supplier for ESSs, it is very important to predict its cycle and power degradation behavior. In particular, the power, one of the hardest electrochemical properties to measure, needs lots of resources such as time and facilities. Due to these difficulties, computer modelling of lithium secondary batteries is applied to predict the DC-IR and power value during charging and discharging as a function of state of charge (SOC) by using pulse-based measurement methods. Moreover, based on the hybrid pulse power characteristics (HPPC) and J-Pulse (JEVS D 713, Japan Electric Vehicle Association Standards) methods, their electrochemical properties are also compared and discussed.