Search

All‐solid‐state sodium batteries offer the advantage of both sustainability and safety. Solid‐state electrolytes play a key role, and an oxygen‐incorporated NaAlCl4 composite electrolyte is presented with a high ambient‐temperature ionic conductivity of > 0.1 mS cm−1. The electrolyte synthesized with a mechanochemical reaction consists of in situ‐formed Al2O3 nanoparticles that provide enhanced conduction through an oxychloride phase at the interface. Magic angle spinning nuclear magnetic resonance spectroscopy confirms the formation of Al2O3 and the oxychloride phases at the interface and sheds insights into the origin of the enhanced ionic conductivity of the composite electrolyte. Additionally, simply adding Al2O3 nanoparticles to NaAlCl4 before mechanochemical synthesis is investigated, and a relationship between Al2O3 surface area and composite electrolyte ionic conductivity is identified. All‐solid‐state sodium batteries assembled with the composite electrolyte demonstrate a high specific capacity of 124 mA h g−1, clearly outperforming the baseline NaAlCl4 electrolyte. Furthermore, X‐ray photoelectron spectroscopy is utilized to understand the origin of capacity fade and obtain insights into electrolyte decomposition products. This work provides a deeper understanding of methods for boosting the ion transport in a low‐cost halide solid electrolyte for practical viability of all‐solid‐state sodium batteries. [ABSTRACT FROM AUTHOR]

Eliminating cobalt from high‐nickel layered oxide cathodes lowers the cost of lithium‐ion batteries for electric vehicles. However, cobalt‐free cathodes with high Mn4+ and Ni2+ contents are prone to Li/Ni mixing after synthesis, potentially compromising battery energy density, rate capability, and cycling stability. Without cobalt facilitating cation ordering in the layered structure, the degree of Li/Ni mixing in cobalt‐free cathodes depends heavily on the calcination conditions. In this study, a systematic exploration of calcination temperatures and LiOH ratio for LiNi0.9Mn0.1O2 (NM‐90) provides detailed insights into the optimal synthesis conditions for high‐capacity cobalt‐free cathodes with extended cycle life. Surprisingly, high Li/Ni mixing does not necessarily lead to poor cycling stability whereas low Li/Ni mixing does not guarantee a long cycle life. More importantly, although excessive calcination temperature can further decrease Li/Ni mixing, it does not necessarily enhance capacity. Instead, the pernicious effects from the H2 → H3 phase transition are amplified due to a pronounced two‐phase reaction. An extensive suite of chemical and structural characterization methods uncovers a correlation between elevated calcination temperature, phase transformation, cation ordering, and capacity fading behavior: "overcooking" high‐nickel, cobalt‐free cathodes induce structural arrangement toward that of LiNiO2, with exacerbated lattice distortion and surface instability accelerating capacity fade. [ABSTRACT FROM AUTHOR]

Single‐crystalline layered oxide (LiNi1‐x‐yMnxCoyO2) cathodes have been found to exhibit exceptional electrochemical properties when coupled with various inorganic solid electrolytes (ISEs) in all‐solid‐state batteries (ASSBs). Their advantages stem from the robust morphological integrity with the absence of grain boundaries and the high electrochemical oxidative stability. Here, ASSBs featuring single‐crystalline LiNiO2 (LNO) with the highest Ni content are reported, offering a high theoretical specific capacity of 275 mAh g‐1 alongside a high average discharge voltage (3.7 V vs Li+/Li). Through a careful investigation, it is demonstrated that micron‐sized single‐crystalline LNO (µSC‐LNO) composite cathodes with a halide ISE exhibit a high initial discharge capacity of 205 mAh g‐1 with an outstanding cycle performance over 200 cycles in room‐temperature ASSBs. The significance of engineering parameters is emphasized, such as particle size and specific density, in promoting a homogeneous and fast Li+ transport within the composite cathodes. Furthermore, the formation of undesirable interphase between the halide ISE in the cathode and sulfide ISE separator is elucidated, which may be a critical factor impeding long‐term cyclability of ASSBs. This work provides insights into the design of composite cathodes for high‐energy‐density ASSBs. [ABSTRACT FROM AUTHOR]

Gas evolution from high‐nickel layered oxide cathodes (>90% Ni) remains a major issue for their practical application. Gaseous species, such as CO2, O2, and CO, that are evolved at high states of charge (SOC) worsen the overall safety of batteries, as pressure build‐up within the cell may lead to cell rupture. Since these gasses are produced during cathode degradation, tracking the formation of gasses is also important in diagnosing cathode failure. Online electrochemical mass spectrometry (OEMS) is a powerful in situ technique to study gas evolution from the cathode during high‐voltage charge. However, the differences in the OEMS experimental setups between different groups make it challenging to compare results between groups. In this perspective, the various factors that influence gas evolution based on the OEMS results collected in this group are presented. The focus is on the conditions that lead to gas release, with a particular emphasis on reactive oxygen formation and subsequent chemical reactions with the electrolyte. Promising strategies, such as electrolytes, compositional tuning, and surface coatings that are effective at suppressing gas evolution from the cathode are highlighted. Critical insights into mitigating cathode degradation and gas evolution are provided to guide the development of safer, high‐energy batteries. [ABSTRACT FROM AUTHOR]

Layered oxide cathodes with a high‐nickel (Ni ≥ 0.9) content exhibit great potential for enabling high‐energy‐density lithium‐ion batteries. However, their practical feasibility and cycle life are hampered by severe surface reactivity with the electrolyte. A LiNi0.90Co0.05Al0.05O2 cathode is presented enriched with Al on the surface (S‐NCA) and benchmark it against a LiNi0.90Co0.05Al0.05O2 cathode obtained by a conventional co‐precipitation method that has a uniform Al distribution throughout the bulk (B‐NCA). The S‐NCA cathode greatly outperform with an impressive capacity retention of 84% after 1000 cycles in pouch full cells with graphite anode compared to 62% retention for B‐NCA. Advanced surface characterization methodologies, including time‐of‐flight secondary‐ion mass spectrometry, reveal that the Al‐enriched surface morphology facilitates the formation of a robust, thin electrode‐electrolyte interphase (EEI), effectively suppressing the oxidative decomposition of the electrolyte, gas generation, and metallic dead lithium formation on graphite anode. The results illustrate that surface reactivity with the electrolyte is the primary factor limiting the cycle of cells with high‐Ni cathodes. The work provides valuable insights toward the practical viability of ultrahigh‐Ni cathodes in lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

Cobalt‐free cathode materials have garnered increased attention for applications in next‐generation batteries for electric vehicles, as cobalt is considered to have at a high supply chain risk. Here, the use of a localized saturated electrolyte (LSE) to enable stable cycling of a cobalt‐free, low‐nickel layered‐oxide cathode LiNi0.7Mn0.25Al0.05O2 (NMA‐70) to higher voltages (4.6 V) in a lithium‐metal battery is demonstrated. Compared to the baseline LP57 electrolyte, the LSE extends the cycle life from ≈100 cycles to ≈400 cycles before reaching 80% capacity retention. Visual indicators of cell degradation, such as product deposition, are observed on electrodes cycled in LP57. It is shown that cycling NMA‐70 in LSE reduces the overall active material loss and overpotential growth during extended cycling. This is attributed to the formation of a beneficial fluorinated interphase layer, a lower degree of rock‐salt phase formation, and a reduction in the gas evolution from the cathode surface. The decrease in gas evolution from the cathode cycled in LSE reflects a lower degree of electrolyte reactivity and an overall improvement in the safety characteristics of the cell. This study highlights the importance of a stable electrolyte to enable the high‐voltage cycling of alternative, lower nickel, and cobalt‐free cathodes. [ABSTRACT FROM AUTHOR]

Electrolytes play a critical role in stabilizing highly reactive lithium‐metal anodes (LMAs) and high‐voltage cathodes for rechargeable lithium‐metal batteries (LMBs). Localized high concentration electrolytes (LHCEs) have achieved remarkable success in the context of LMBs. However, the state‐of‐the‐art LHCEs are based on LiFSI salt, which is prohibitively expensive. Here, the utility of low‐cost LiPF6 salt in localized saturated electrolytes (LSEs) with a series of solvents and diluents in LMBs with cobalt‐free LiNiO2 cathode is systematically explored. Experimental and theoretical analyses reveal that the unique solvation structure formed not only changes the distribution of solvents and anions but also alters the atom–atom distances within them, leading to different reduction and oxidation stabilities compared to low‐concentration electrolytes. In addition, LSEs help form LiF‐rich interphase layers on the LMA and LiNiO2 cathode, protecting the electrodes from degradation during cycling. Different LSEs also lead to differences in lithium plating morphology and impedance buildup during cycling, impacting the performance of LMBs. The solvent and diluent must be carefully selected for compatibility with a lithium salt when developing LHCEs and LSEs for LMBs. [ABSTRACT FROM AUTHOR]

Lithium–sulfur batteries offer the advantage of high energy density at a low cost, but their viability is hindered by the polysulfide shuttle effect, sluggish reaction kinetics, and dendritic Li growth. To address these persistent challenges in a unified manner, a dual‐function, flexible, free‐standing framework by coupling catalytic and lithiophilic 1T′‐MoTe2 nanosheets with conductive carbon nanotubes (MoTe2‐CNT), which serve as a host for both a sulfur cathode (S/MoTe2‐CNT) and a lithium‐metal anode (MoTe2‐CNT/Li) is presented here. MoTe2‐CNT not only guides a uniform growth of lithium within the framework, but also forms a thin, unique sulfide‐rich solid‐electrolyte interphase (SEI) composed of lithium thiotellurate on the Li surface when paired with a sulfur cathode. This SEI stabilizes Li deposition, suppresses electrolyte decomposition, and prevents Li loss, thereby prolonging cycle life. Full coin cells with a very low negative to positive electrode capacity ratio of ≈2.5 and a high areal capacity of 7.6 mA h cm−2 display 75% capacity retention after 500 cycles. The pouch cells fabricated with MoTe2‐CNT deliver a high capacity of 1533 mA h g−1 and energy density of 319 Wh kg−1 at a low electrolyte‐to‐capacity ratio of ≈2.9 µL [mA h]−1 and a low electrolyte‐to‐sulfur ratio of 4.5 µL mg−1. [ABSTRACT FROM AUTHOR]