All-solid-state Li batteries (ASSBs) promise better performance and higher safety than the current liquidbased Li-ion batteries (LIBs). Sulfide ASSBs have been extensively studied and considerably advanced in recent decades. Research on identifying suitable cathode materials for sulfide ASSBs is currently well established, with great progress being made in the commercialization of layered cathodes in the liquid-based LIBs. Research on anode materials for sulfide ASSBs is of great importance for enhancing the battery energy density. However, it seems that little has been published that summarizes studies of anode materials for sulfide ASSBs and suggests future research directions. Thus, within this Minireview, we aim to provide an overview of previous and current research focused on anode materials for sulfide ASSBs and to suggest a future research direction for developing suitable anode systems for sulfide ASSBs.

All‐solid‐state Li batteries (ASSBs) promise better performance and higher safety than the current liquid‐based Li‐ion batteries (LIBs). Sulfide ASSBs have been extensively studied and considerably advanced in recent decades. Research on identifying suitable cathode materials for sulfide ASSBs is currently well established, with great progress being made in the commercialization of layered cathodes in the liquid‐based LIBs. Research on anode materials for sulfide ASSBs is of great importance for enhancing the battery energy density. However, it seems that little has been published that summarizes studies of anode materials for sulfide ASSBs and suggests future research directions. Thus, within this Minireview, we aim to provide an overview of previous and current research focused on anode materials for sulfide ASSBs and to suggest a future research direction for developing suitable anode systems for sulfide ASSBs.

Lithium-ion batteries (LIBs) continue to dominate the battery market with their efficient energy storage abilities and their ongoing development. However, at high charge/discharge C-rates their electrochemical performance decreases significantly. To improve the power density properties of LIBs, it is important to form a uniform electron transfer network in the cathode electrode via the addition of conductive additives. Carbon nanotubes (CNTs) with high crystallinity, high electrical conductivity, and high aspect ratio properties have gathered significant interest as cathode electrode conductive additives. However, due to the high aggregational properties of CNTs, it is difficult to form a uniform network for electron transfer within the electrode. In this study, to help fabricate electrodes with well-dispersed CNTs, various electrodes were prepared by controlling (i) the mixing order of the conductive material, binder, and active material, and (ii) the sonication process of the CNTs/NMP solution before the electrode slurry preparation. When the binder was mixed with a well sonicated CNTs/NMP solution, the CNTs uniformly adsorbed to the then added cathode material of LiNi0.6Co0.2Mn0.2O2 and were well-dispersed to form a flowing uniform network. This electrode fabrication process achieved > 98.74% capacity retention after 50 cycles at 5C via suppressed polarization at high current densities and a more reversible H1-M phase transition of the active material. Our study presents a novel design benchmark for the fabricating of electrodes applying well-dispersed CNTs, which can facilitate the application of LIBs in high current density applications.

long-range electric vehicle applications, especially those with high Ni contents as they deliver high capacity under the same operation protocol. [1][2][3] However, this increase in Ni content brings with it a rapid capacity fade and a shorter overall battery lifetime. [4][5][6] This capacity fade is linked to the oxygen loss at highly delithiated states. The occurrence of the oxygen loss is related to the unstable Ni ions that propagate from the surface of the NCM material into the bulk. This adverse effect is significantly promoted particularly in high-Ni NCM materials (Ni ≥ 80%). [7,8] When exposed to ambient environmental conditions, degradation of high-Ni NCM occurs from the surface, generating problematic residual lithium compounds. [9] The reaction of high-Ni NCM with H 2 O and CO 2 of the ambient air spawns a variety of the inhibiting lithium compounds on the surface. [10][11][12] Surface carbonates such as Li 2 CO 3 and surface hydroxides such as LiOH deteriorate the initial capacity and cyclability as they can result in unwanted side reactions and gas production during charge/discharge cycles. [13,14] The surface contaminants can also accelerate electrolyte decomposition and hamper the cycle capabilities. These surface contaminants are one of the key problems affecting the battery manufacturing industry. [15] Determinations of the exact degradation mechanisms have been attempted to promote understanding and develop potential mitigation strategies. Jung et al. showed that the extreme ambient degradation associated with LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) is due to the presence of Ni, which then leads to the extraction of Ni from the layered structure. [10] The findings were impactful in developing the idea that surface contaminants may be formed along with structural degradation of the cathode; however, the work was unable to offer a standalone solution to the problem. Strategies to overcome surface degradation in general are numerous, however, strategies to prevent ambient atmosphere exposure-based surface degradation are limited. Liu et al. suggest a recovery method via heating the NCM at 725 °C to achieve a full recovery of the material. [16] This was successful, however, requiring a recovery step is undesirable for battery cell manufacturers and still requires a completely inert atmosphere after heating and during cell manufacturing to prevent further degradation. Furthermore, the posttreatment of NCM materials after storage was proven to eventually lead The mainstream of high-energy cathode development is focused on increasing the Ni-ratio in layered structured cathode materials. The increment of the Ni portion in the layered cathode material escalates not only the deliverable capacity but also the structural degradation. High-Ni layered cathodes are highly vulnerable to exposure to air that contains CO 2 and H 2 O, forming problematic residual lithium compounds at the surface. In this work, a novel air-and moisture robust surface modification is reported for LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) via ...

of Ni-rich cathodes under the same operating conditions, the volumetric energy density of LCO (2500 Wh L −1 ) can be greater than that of Ni-rich cathodes (e.g., Ni 0.85 Co 0.13 Al 0.02 O 2 : 2180 Wh L −1 ). [3,4] The higher volumetric energy density of LCO is attributed to the higher electrode density of LCO (4.0 g cm −3 ) compared to that of Ni 0.85 Co 0.13 Al 0.02 O 2 : (3.0 g cm −3 ), because the volumetric energy density is obtained as the product of specific capacity, working voltage and electrode density. [3,4] Therefore, improving the cycling stability of LCO at higher cutoff voltages is a more effective approach for developing cathode materials with high volumetric energy densities. Although there are strategies for the improved cycling stability of LCO at a higher cutoff voltage, [5] increasing the operating voltage mainly produces a significant structural stress on the LCO structure. If LCO releases more than 0.6 mol of Li ions, then its electrochemical reversibility drastically degenerates because of the irreversible phase transition. [6] A well-structured LCO has an O3-type stacking sequence, which should be maintained during the cycling. [7] In a highly delithiated state, oxygen-ion repulsion around the Li-slabs is not effectively compensated owing to Li-site vacancies and causing slipping of the transition metal-oxygen (TM-O) layers. [8] The recent development of high-energy LiCoO 2 (LCO) and progress in the material recycling technology have brought Co-based materials under the limelight, although their capacity still suffers from structural instability at highly delithiated states. Thus, in this study, a secondary doping ion substitution method is proposed to improve the electrochemical reversibility of LCO materials for Li-ion batteries. To overcome the instability of LCO at highly delithiated states, Na ions are utilized as functional dopants to exert the pillar effect at the Li sites. In addition, Fe-ion substitution (secondary dopant) is performed to provide thermodynamically stable surroundings for the Na-ion doping. Density functional theory calculations reveal that the formation energy for the Na-doped LCO is significantly reduced in the presence of Fe ions. Na and Fe doping improve the capacity retention as well as the average voltage decay at a cutoff voltage of 4.5 V. Furthermore, structural analysis indicates that the improved cycling stability results from the suppressed irreversible phase transition in the Na-and Fe-doped LCO. This paper highlights the fabrication of high-energy Co-rich materials for high voltage operations, via a novel ion substitution method, indicating a new avenue for the manufacturing of layered cathode materials with a long cycle life.