High-nickel layered oxide cathodes are becoming appealing for lithium-ion batteries employed in portable electronics and electric vehicles because of their higher energy density, low or no cobalt ...content, and ability to be manufactured with existing infrastructure. However, high-nickel layered oxides are plagued by the formation of residual lithium species, such as LiOH and Li2CO3, on the surface, which are detrimental to the manufacturing process and performance. Despite the problems residual lithium causes for the industry, academia mainly focuses on the safety risks and electrochemical impacts of residual lithium. In this Perspective, we examine the residual lithium problem through a lens of its impact on cathode slurry instability and large-scale manufacturing of high-nickel layered oxides. Additionally, methods of measuring residual lithium are discussed from the perspective of their accuracy as well as practicality in the manufacturing process. We hope that this Perspective would encourage the academic endeavor to consider the practical obstacles caused by residual lithium on the industrialization of high-nickel layered oxides and their mitigation, while attempting to improve their electrochemical performance and safety through doping, surface modifications, or other approaches.
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Fabricating inorganic-organic hybrid perovskite solar cells (PSCs) on plastic substrates broadens their scope for implementation in real systems by imparting portability, conformability and allowing ...high-throughput production, which is necessary for lowering costs. Here we report a new route to prepare highly dispersed Zn2SnO4 (ZSO) nanoparticles at low-temperature (<100 °C) for the development of high-performance flexible PSCs. The introduction of the ZSO film significantly improves transmittance of flexible polyethylene naphthalate/indium-doped tin oxide (PEN/ITO)-coated substrate from ∼75 to ∼90% over the entire range of wavelengths. The best performing flexible PSC, based on the ZSO and CH3NH3PbI3 layer, exhibits steady-state power conversion efficiency (PCE) of 14.85% under AM 1.5G 100 mW·cm(-2) illumination. This renders ZSO a promising candidate as electron-conducting electrode for the highly efficient flexible PSC applications.
The rampant generation of lithium hydroxide and carbonate impurities, commonly known as residual lithium, is a practical obstacle to the mass‐scale synthesis and handling of high‐nickel (>90 %) ...layered oxides and their use as high‐energy‐density cathodes for lithium‐ion batteries. Herein, we suggest a simple in situ method to control the residual lithium chemistry of a high‐nickel lithium layered oxide, Li(Ni0.91Co0.06Mn0.03)O2 (NCM9163), with minimal side effects. Based on thermodynamic considerations of the preferred reactions, we systematically designed a synthesis process that preemptively converts residual Li2O (the origin of LiOH and Li2CO3) into a more stable compound by injecting reactive SO2 gas. The preformed lithium sulfate thin film significantly suppresses the generation of LiOH and Li2CO3 during both synthesis and storage, thereby mitigating slurry gelation and gas evolution and improving the cycle stability.
A simple in situ method to control the residual lithium in high‐nickel lithium layered oxide is designed. Residual Li2O (the origin of LiOH and Li2CO3) is preemptively converted into the Li2SO4 thin film by injecting SO2 gas during calcination. This method suppresses the generation of LiOH and Li2CO3 during both synthesis and storage, thereby mitigating slurry gelation and gas evolution and improving cycle stability.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Anatase TiO2 is considered as one of the promising anodes for sodium‐ion batteries because of its large sodium storage capacities with potentially low cost. However, the precise reaction mechanisms ...and the interplay between surface properties and electrochemical performance are still not elucidated. Using multimethod analyses, it is herein demonstrated that the TiO2 electrode undergoes amorphization during the first sodiation and the amorphous phase exhibits pseudocapacitive sodium storage behaviors in subsequent cycles. It is also shown that the pseudocapacitive sodium storage performance is sensitive to the nature of solid electrolyte interphase (SEI) layers. For the first time, it is found that ether‐based electrolytes enable the formation of thin (≈2.5 nm) and robust SEI layers, in contrast to the thick (≈10 nm) and growing SEI from conventional carbonate‐based electrolytes. First principle calculations suggest that the higher lowest unoccupied molecular orbital energies of ether solvents/ion complexes are responsible for the difference. TiO2 electrodes in ether‐based electrolyte present an impressive capacity of 192 mAh g−1 at 0.1 A g−1 after 500 cycles, much higher than that in carbonate‐based electrolyte. This work offers the clarified picture of electrochemical sodiation mechanisms of anatase TiO2 and guides on strategies about interfacial control for high performance anodes.
A thin and robust solid electrolyte interphase formed on a TiO2 surface that is enabled by using ether electrodes is demonstrated in Na‐ion batteries. This electrolyte/electrolyte interface, which is superior to conventional carbonate electrolyte, results in largely different electrochemical performances. The fundamental origin of the difference is unveiled through the combination of intensive experimental characterizations and first principles calculations.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Lithium-ion batteries are expected to serve as a key technology for large-scale energy storage systems (ESSs), which will help satisfy recent increasing demands for renewable energy utilization. ...Besides their promising electrochemical performance, the low self-discharge rate (<5% of the stored capacity over 1 month) of lithium-ion batteries is one of their most significant advantages for ESSs. Herein, contrary to conventional belief, we report that the self-discharge of LIBs can be abnormally accelerated when the battery has been exposed even to a routine short-term thermal exposure. We demonstrate that this thermal ‘history’ in addition to the temperature itself is memorized in the battery and accelerates the self-discharge rate. The series of characterizations performed in our work reveal that the electrolyte salt acts as a strong oxidizing agent by vigorously damaging the surface of the cathode, producing an internal ‘parasitic’ lithium source that continuously supplies lithium for the self-discharge. Although it is widely known that battery operation at elevated temperature generally induces faster degradation of capacity over multiple cycles, the key finding here is that not only the operation temperature but also the ‘thermal history’ of the battery should be carefully considered because this history remains and continues to affect the self-discharge rate afterwards. The self-discharge of LIBs has remained largely neglected; however, our findings suggest that close attention must be paid to the self-discharge of LIBs applied to large-scale ESSs, which, unlike mobile electronic devices, will be exposed to various outdoor temperature conditions.
The development of a high‐performance oxygen evolution reaction (OER) catalyst is pivotal for the practical realization of a water‐splitting system. Although an extensive search for OER catalysts has ...been performed in the past decades, cost‐effective catalysts remain elusive. Herein, an amorphous cobalt phyllosilicate (ACP) with layered crystalline motif prepared by a room‐temperature precipitation is introduced as a new OER catalyst; this material exhibits a remarkably low overpotential (η ≈ 367 mV for a current density of 10 mA cm−2). A structural investigation using X‐ray absorption spectroscopy reveals that the amorphous structure contains layered motifs similar to the structure of CoOOH, which is demonstrated to be responsible for the OER catalysis based on density functional theory calculations. However, the calculations also reveal that the local environment of the active site in the layered crystalline motif in the ACP is significantly modulated by the silicate, leading to a substantial reduction of η of the OER compared with that of CoOOH. This work proposes amorphous phyllosilicates as a new group of efficient OER catalysts and suggests that tuning of the catalytic activity by introducing redox‐inert groups may be a new unexplored avenue for the design of novel high‐performance catalysts.
The amorphous cobalt phyllosilicate introduced in this study exhibits the basic nature of a phyllosilicate as well as superior oxygen evolution reaction (OER) catalytic activity. Density functional theory calculations on the OER mechanism suggest that the silicate component aids in substantially reducing the η of the catalytic active sites by modulating the local structure.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Cobalt‐free layered lithium‐rich nickel manganese oxides, LiLixNiyMn1−x−yO2 (LLNMO), are promising positive electrode materials for lithium rechargeable batteries because of their high energy density ...and low materials cost. However, substantial voltage decay is inevitable upon electrochemical cycling, which makes this class of materials less practical. It has been proposed that undesirable voltage decay is linked to irreversible structural rearrangement involving irreversible oxygen loss and cation migration. Herein, the authors demonstrate that the voltage decay of the electrode is correlated to Mn4+/Mn3+ redox activation and subsequent cation disordering, which can be remarkably suppressed via simple compositional tuning to induce the formation of Ni3+ in the pristine material. By implementing our new strategy, the Mn4+/Mn3+ reduction is subdued by an alternative redox reaction involving the use of pristine Ni3+ as a redox buffer, which has been designed to be widened from Ni3+/Ni4+ to Ni2+/Ni4+, without compensation for the capacity in principle. Negligible change in the voltage profile of modified LLNMO is observed upon extended cycling, and manganese migration into the lithium layer is significantly suppressed. Based on these findings, we propose a general strategy to suppress the voltage decay of Mn‐containing lithium‐rich oxides to achieve long‐lasting high energy density from this class of materials.
A novel strategy to suppress the voltage decay in layered lithium‐rich nickel manganese oxides is demonstrated using a Ni redox buffer. A substitution of Mn with Ni in lithium‐rich nickel manganese oxides results in the deactivation of Mn reduction, which is compensated by Ni redox reaction. Mn deactivation reduces the undesirable phase transformation, eventually leading to the suppression of the voltage decay.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The practical realization of a water-splitting system necessitates the development of high-performance oxygen evolution reaction (OER) catalysts. Despite tremendous research efforts aimed at ...identifying earth-abundant 3d transition-metal-based catalysts, their insufficient catalytic efficiencies continue to jeopardize their real-world application. Herein, we introduce amorphous cobalt-iron phyllosilicates (ACFPs) as highly efficient OER catalysts. The ACFPs were designed by tailoring the metal chemistry of the phyllosilicate framework which consists of laminations of silicate (SiO
4
) layers and layered Co-Fe (oxy)hydroxide motifs, and prepared using a facile room-temperature precipitation method. It is demonstrated that the OER properties/mechanisms are sensitively affected by the Co/Fe ratio, with an exceptionally low overpotential (
η
∼ 329 mV for a current density of 10 mA cm
−2
) delivered at the optimized composition of 40 at% Fe. This catalytic efficiency is greater than that of the structurally analogous Co-Fe (oxy)hydroxide as well as those of pure Co or Fe phyllosilicate, suggesting the beneficial role of the phyllosilicate framework along with the synergistic interplay of Co and Fe ions in the framework. Density functional theory calculations revealed that the introduction of Fe at the surface of Co phyllosilicate perturbs the local structural environment of oxygen sites, providing additional active sites. This work proposes a valid strategy for the design of high-performance catalysts by chemically tuning both the redox-active and redox-inert elements concomitantly in novel multinary phyllosilicate-based OER catalysts.
For the high-performance oxygen evolution reaction catalysts, we introduce amorphous cobalt-iron phyllosilicates (ACFPs), which explore the chemical space of phyllosilicate materials.
The thermodynamic instability of the LiCoO2 layered structure at >0.5Li extraction has been considered an obstacle for the reversible utilization of its near theoretical capacity at high cutoff ...voltage (>4.6 V vs Li/Li+) in lithium-ion batteries. Many previous studies have focused on resolving this issue by surface modification of LiCoO2, which has proven to be effective in suppressing phase transformation. To determine the extent to which surface protection of LiCoO2 is effective despite its thermodynamic instability and presumably incomplete reversibility involving the O1 phase, here we verify the intrinsic reversibility of bulk LiCoO2 with extended lithium extraction by ruling out the effect of a surface. Specifically, first, we show that, contrary to conventional belief, electrochemical cycling of LiCoO2 at a cutoff voltage of 4.8 V (vs Li/Li+) results in better cycle stability and lower polarizations than those at 4.6 V. We demonstrate, using an exhaustive suite of characterization tools, that the rapid cycle degradation under high-voltage cycling is mostly caused by the formation of a surface resistive layer; however, these damaged surfaces are leached out faster than they are accumulated above a certain potential, which results in superior cyclability compared with that achieved for less oxidative 4.6-V cycling. This beneficial leaching out of the resistive surface layer serves as a “subtractive” surface modification and plays a role in enhancing the cycle stability and is distinguished from conventional “additive” surface modification such as coating. This approach allows us to decouple factors of the bulk and surface degradations that contribute to the capacity fade and leads to the finding that, in the absence of a resistive surface, the capacity retention of a LiCoO2 electrode with 4.8-V cutoff cycling can be intrinsically high, indicating that the instability of the crystalline Li x CoO2 (x < 0.5) has a limited effect on the cycle stability. Our findings also explain why the strategy of coating foreign materials on the surface of LiCoO2 can improve the high-voltage cycling to some extent despite the expected thermodynamic instability of the highly charged phase.
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