Tom James Embleton

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.

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 CO₂ and H₂O, forming problematic residual lithium compounds at the surface. In this work, a novel air‐ and moisture robust surface modification is reported for LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) via the sol‐gel coating method that selectively coats the internal surface area of the polycrystalline morphology secondary particles. Bare‐, Li₂SnO₃‐coated and LiCoO₂‐coated NCM811 are exposed to different ambient environments (air, hot‐air, and moisture‐air) to systematically investigate the correlation between the internal/external coating morphology and performance degradations. The LiCoO₂‐coated NCM811s exhibit high‐capacity retention after exposure to all environments, due to the internal surface coating that prevents the penetration of harmful compounds into the polycrystalline NCM811. On the other hand, the Li₂SnO₃‐coated NCM811s exposed to the ambient environments show gradual capacity fading, implying the occurrence of internal degradation. This paper highlights the impact of the internal degradation of polycrystalline NCM811 after environmental exposure and the correct coating mechanisms required to successfully prevent it.

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 LiNi_0.6Co_0.2Mn_0.2O₂ 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.

The recent development of high‐energy LiCoO₂ (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.

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.

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.

Despite the recent advancement of sulfide all-solid-state lithium batteries, the choice of their respective components yet requires further comprehensive investigations into their functionality and compatibility. While the development of cathode materials and sulfide electrolytes appears to be greatly advanced, there seems a lack of attention on carbon conductive additives. As sulfide electrolytes are instable with conventional carbon conductive additives, it is necessary to develop conductive additives with a satisfactory electronic conductivity and good chemical/electrochemical stability with sulfide electrolytes. This study proposes a new mixed conductor based on carbon nanofiber (CNF), namely lithium-enhanced functionalized carbon nanofiber (LF-CNF), exhibiting a greatly enhanced Li-ion conductivity with a little compensation of their electronic conductivity. By utilizing LF-CNF, a discharge capacity of 198mAh g -1 at 0.05C and 148mAh g -1 after 50 cycles at 0.1C were achieved from the cathode composite of LiNi 0.8 Co 0.1 Mn 0.1 O 2 , argyrodite solid electrolyte and LF-CNF (70:30:5 in mass). Furthermore, LF-CNF appears to reduce detrimental cation mixing after storage in Ar-atmosphere over one month and at high voltage cycling of 4.5V. Our work highlights that the conductivity tuning of conductive additives offers a great performance enhancement for high-energy sulfide electrolyte based solid-state batteries.