The stability and kinetics of the Li–Li7La3Zr2O12 (LLZO) interface were characterized as a function of temperature and current density. Polycrystalline LLZO was densified using a rapid hot-pressing ...technique achieving 97 ± 1% relative density, and <10% grain boundary resistance; effectively consisting of an ensemble of single LLZO crystals. It was determined that by heating to 175 °C, the room temperature Li-LLZO interface resistance decreases dramatically from 5822 (as-assembled) to 514 Ω cm2; a > 10-fold decrease. In characterizing the maximum sustainable current density (or critical current density – CCD) of the Li-LLZO interface, several signs of degradation were observed. In DC cycling tests, significant deviation from Ohmic behavior was observed. In post-cycling tests, regions of metallic Li were observed; propagating parallel to the ionic current. For the cells cycled at 30, 70, 100, 130 and 160 °C, the CCD was determined to be 50, 200, 800, 3500, and 20000 μA cm−2, respectively. The relationships and phenomena observed in this work can be used to better understand the Li-LLZO interface stability, enabling the use of batteries employing Li metal anodes.
•The Li-LLZO interface kinetics and stability are affected by temperature.•The Li-LLZO interface resistance decreases by >10-fold upon heating to 175 °C.•Reducing the charge-transfer resistance increased the maximum current density.•Exceeding the maximum current density resulted in metallic Li propagation.
Herein we report on a general approach to delaminate multi-layered MXenes using an organic base to induce swelling that in turn weakens the bonds between the MX layers. Simple agitation or mild ...sonication of the swollen MXene in water resulted in the large-scale delamination of the MXene layers. The delamination method is demonstrated for vanadium carbide and titanium carbonitride MXenes.
Solid-state Li-ion batteries employing a metallic lithium anode in conjunction with an inorganic solid electrolyte (ISE) are expected to offer superior energy density and cycle life. The realization ...of these metrics critically hinges on the simultaneous optimization of the ISE and the two electrode/electrolyte interfaces. In this Opinion article, we provide an overview of the materials and interfacial challenges that limit the performance of solid-state lithium metal batteries (SSLMBs). Owing to the importance of the Li/ISE interface, we dedicate a large section of this article to discuss the mechanistic aspects of lithium deposition at the Li/ISE interface. We further discuss a few recently proposed mechanisms that rationalize the growth of lithium through ISEs. We conclude our review with a brief discussion on the anode-free approach for fabricating SSLMBs where metallic lithium is generated in-situ from pre-lithiated cathodes.
Solid-state batteries are considered the holy grail of next-generation battery technology, meeting the ever-increasing demand for energy storage that is affordable and safe, with high energy density ...and long cycle life. Materials and interfaces play a critical role for their eventual success and mass commercialization. This issue of MRS Bulletin focuses on the current state of the art of solid-state electrolytes and device architectures and provides a perspective into the various materials and interfacial challenges that limit its performance and stability.
Large scale synthesis and delamination of 2D Mo2CT
x
(where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary ...transition metal carbide Mo2Ga2C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free‐standing Mo2CT
x
films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor‐like behavior of this MXene, in contrast to Ti3C2T
x
which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 μm thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm−3 in a 1 m sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g−1 are obtained. Free‐standing Mo2CT
x
films, with ≈8 wt% carbon nanotubes, perform well when tested as an electrode material for Li‐ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g−1, respectively, are achieved for over 1000 cycles.
2D Mo2C (MXene) is produced using different synthesis routes, which lead to different flake morphologies. Mo2C exhibits a semiconductor‐like increase in resistivity from 300 to 10 K. Mo2C electrodes in a supercapacitor achieve 700 F cm−3 capacitance in 1 m H2SO4 for 10,000 cycles. Mo2C–Carbon nano tube (CNT) electrodes possess 250 mAh g−1 capacity for 1000 cycles, showing promise as anode for batteries and Li‐ion capacitors.
Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte that could enable solid-state-batteries (SSB) employing metallic Li anodes. For a SSB to be viable, the stability and charge transfer ...kinetics at the Li-LLZO interface should foster facile plating and stripping of Li. Contrary to these goals, recent studies have reported high Li-LLZO interfacial resistance which was attributed to a contamination layer that forms upon exposure of LLZO to air. This study clarifies the mechanisms and consequences associated with air exposure of LLZO; additionally, strategies to minimize these effects are described. First-principles calculations reveal that LLZO readily reacts with humid air; the most favorable reaction pathway involves protonation of LLZO and formation of Li2CO3. X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy were used to characterize the surface and subsurface chemistry of LLZO as a function of relative humidity and exposure time. Additionally, electrochemical impedance spectroscopy was used to measure the Li-LLZO interfacial resistance as a function of surface contamination. These data indicate that air exposure-induced contamination impacts the interfacial resistance significantly, when exposure time exceeds 24 h. The results of this study provide valuable insight into the sensitivity of LLZO to air and how the effects of air contamination can be reversed.
Herein, we report on the electrochemical performance of two-dimensional transition metal carbonitrides as novel promising electrode materials in K-ion batteries. Titanium carbonitride, Ti
CNT
, was ...investigated in detail using electrochemical galvanostatic cycling at various current densities. X-ray diffraction and X-ray photoelectron spectroscopy were used to study the potassiation mechanism and its structural changes.
Accurately identifying the local structural heterogeneity of complex, disordered amorphous materials such as amorphous silicon is crucial for accelerating technology development. However, short-range ...atomic ordering quantification and nanoscale spatial resolution over a large area on a-Si have remained major challenges and practically unexplored. We resolve phonon vibrational modes of a-Si at a lateral resolution of <60 nm by tip-enhanced Raman spectroscopy. To project the high dimensional TERS imaging to a two-dimensional manifold space and categorize amorphous silicon structure, we developed a multiresolution manifold learning algorithm. It allows for quantifying average Si-Si distortion angle and the strain free energy at nanoscale without a human-specified physical threshold. The multiresolution feature of the multiresolution manifold learning allows for distilling local defects of ultra-low abundance (< 0.3%), presenting a new Raman mode at finer resolution grids. This work promises a general paradigm of resolving nanoscale structural heterogeneity and updating domain knowledge for highly disordered materials.
Lithium-rich and manganese-rich (LMR) layered transition metal (TM) oxide composites with general formula xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, Mn) are promising cathode candidates for high energy density ...lithium ion batteries. Lithium-manganese-rich TM oxides crystallize as a nanocomposite layered phase whose structure further evolves with electrochemical cycling. Raman spectroscopy is a powerful tool to monitor the crystal chemistry and correlate phase changes with electrochemical behavior. While several groups have reported Raman spectra of lithium rich TM oxides, the data show considerable variability in terms of both the vibrational features observed and their interpretation. In this study, Raman microscopy is used to investigate lithium-rich and manganese-rich TM cathodes as a function of voltage and electrochemical cycling at various temperatures. No growth of a spinel phase is observed within the cycling conditions. However, analysis of the Raman spectra does indicate the structure of LMR-NMC deviates significantly from an ideal layered phase. The results also highlight the importance of using low laser power and large sample sizes to obtain consistent data sets.
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