Search

Li metal anode coupled with solid-state electrolyte is regarded as an important step for next-generation high-energy batteries to boost the performance of electric vehicles. However, commercialization of Li metal anode in all-solid-state batteries have faced challenges, one of which is the interfacial instability originated during battery operation. To overcome the difficulties in characterizing such interfaces due to their sensitivity to beam and ambient air, we applied cryogenic electron microscopy to unravel the stable nature of Li metal/LiPON interface that has exhibited remarkable electrochemical cyclability. An 80-nm-thick interphase with concentration gradients of N and P was observed, with decomposition products embedded in an amorphous matrix and exhibiting a multilayer-mosaic structure. The findings and methodology in this work give rise to a mechanistic understanding of the stability of Li metal/LiPON interface and can then be extended to study other solid-solid interfaces.

Stable lattice oxygen redox (l-OR) is the key enabler for achieving attainable high energy density in Li-rich layered oxide cathode materials for Li-ion batteries. However, the unique local structure response to oxygen redox in these materials, resulting in energy inefficiency and hysteresis, still remains elusive, preventing their potential applications. By combining the state-of-the-art neutron pair distribution function with crystal orbital overlap analysis, we directly observe the distinct local structure adaption originated from the potential O–O chemical bonds. The structure adaptability is optimized based on the nature of multi transition metals in our model compound Li1.2Ni0.13Mn0.54Co0.13O2, which accommodates the oxygen redox and at the same time preserves the global layered structure. These findings not only advance the understanding of l-OR, but also provide new perspectives in the rational design of high-energy-density cathode materials with reversible and stable l-OR.

Lithium metal is viewed as the ultimate battery anode because of its high theoretical capacity and low electrode potential, but its implementation has been limited by low Coulombic efficiency and dendrite formation above a critical current density. Determining the fundamental properties dictating lithium metal plating-stripping behavior is challenging because characterization techniques are limited by the sensitivity of lithium metal to damage by external probes, which regularly results in altered morphology and chemistry. Motivated by recent application of cryogenic transmission electron microscopy (cryo-TEM) to characterize lithium metal at the atomic scale, we explore the cryogenic focused ion beam (cryo-FIB) method as a quantitative tool for characterizing the bulk morphology of electrochemically deposited lithium and as a technique that enables TEM observation of Li-metal/solid-state electrolyte interfaces. This work highlights the importance of cryo-FIB methodology for preparing sensitive battery materials and elucidates the impact of electrolyte selection on the density and morphology of plated lithium.

Solid-state electrolytes can offer improved lithium-ion battery safety while potentially increasing the energy density by enabling alkali metal anodes. There have been significant research efforts to improve the ionic conductivity of solid-state electrolytes and the electrochemical performance of all-solid-state batteries; however, the root causes of their poor performance - interfacial reaction and subsequent impedance growth - are poorly understood. This is due to the dearth of effective characterization techniques for probing these buried interfaces. In situ and operando methodologies are currently under development for solid-state interfaces, and they offer the potential to describe the dynamic interfacial processes that serve as performance bottlenecks. This article highlights state-of-the-art solid-solid interface probing methodologies, describes practical limitations, and describes a future for dynamic interfacial characterization.

Abstract

Defects and their interactions in crystalline solids often underpin materialproperties and functionality as they are decisive for stability, result inenhanced diffusion, and act as a reservoir of vacancies. Recently, lithium-richlayered oxides have emerged among the leading candidates for thenext-generation energy storage cathode material, delivering 50 % excesscapacity over commercially used compounds. Oxygen-redox reactions are believedto be responsible for the excess capacity, however, voltage fading hasprevented commercialization of these new materials. Despite extensive researchthe understanding of the mechanisms underpinning oxygen-redox reactions andvoltage fade remain incomplete. Here, using operando three-dimensional Braggcoherent diffractive imaging, we directly observe nucleation of a mobiledislocation network in nanoparticles of lithium-rich layered oxide material.Surprisingly, we find that dislocations form more readily in the lithium-richlayered oxide material as compared with a conventional layered oxide material,suggesting a link between the defects and the anomalously high capacity inlithium-rich layered oxides. The formation of a network of partial dislocationsdramatically alters the local lithium environment and contributes to thevoltage fade. Based on our findings we design and demonstrate a method torecover the original high voltage functionality. Our findings reveal that thevoltage fade in lithium-rich layered oxides is reversible and call for newparadigms for improved design of oxygen-redox active materials.

Defects and their interactions in crystalline solids often underpin materialproperties and functionality as they are decisive for stability, result inenhanced diffusion, and act as a reservoir of vacancies. Recently, lithium-richlayered oxides have emerged among the leading candidates for thenext-generation energy storage cathode material, delivering 50 % excesscapacity over commercially used compounds. Oxygen-redox reactions are believedto be responsible for the excess capacity, however, voltage fading hasprevented commercialization of these new materials. Despite extensive researchthe understanding of the mechanisms underpinning oxygen-redox reactions andvoltage fade remain incomplete. Here, using operando three-dimensional Braggcoherent diffractive imaging, we directly observe nucleation of a mobiledislocation network in nanoparticles of lithium-rich layered oxide material.Surprisingly, we find that dislocations form more readily in the lithium-richlayered oxide material as compared with a conventional layered oxide material,suggesting a link between the defects and the anomalously high capacity inlithium-rich layered oxides. The formation of a network of partial dislocationsdramatically alters the local lithium environment and contributes to thevoltage fade. Based on our findings we design and demonstrate a method torecover the original high voltage functionality. Our findings reveal that thevoltage fade in lithium-rich layered oxides is reversible and call for newparadigms for improved design of oxygen-redox active materials.

We have used soft x-ray photoemission electron microscopy to image the magnetization of single-domain La0.7Sr0.3MnO3 nanoislands arranged in geometrically frustrated configurations such as square ice and kagome ice geometries. Upon thermal randomization, ensembles of nanoislands with strong interisland magnetic coupling relax towards low-energy configurations. Statistical analysis shows that the likelihood of ensembles falling into low-energy configurations depends strongly on the annealing temperature. Annealing to just below the Curie temperature of the ferromagnetic film (TC=338K) allows for a much greater probability of achieving low-energy configurations as compared to annealing above the Curie temperature. At this thermally active temperature of 325 K, the ensemble of ferromagnetic nanoislands explore their energy landscape over time and eventually transition to lower energy states as compared to the frozen-in configurations obtained upon cooling from above the Curie temperature. Thus, this materials system allows for a facile method to systematically study thermal evolution of artificial spin ice arrays of nanoislands at temperatures modestly above room temperature.

We have used soft x-ray photoemission electron microscopy to image the magnetization of single-domain La0.7Sr0.3MnO3 nanoislands arranged in geometrically frustrated configurations such as square ice and kagome ice geometries. Upon thermal randomization, ensembles of nanoislands with strong interisland magnetic coupling relax towards low-energy configurations. Statistical analysis shows that the likelihood of ensembles falling into low-energy configurations depends strongly on the annealing temperature. Annealing to just below the Curie temperature of the ferromagnetic film (TC=338K) allows for a much greater probability of achieving low-energy configurations as compared to annealing above the Curie temperature. At this thermally active temperature of 325 K, the ensemble of ferromagnetic nanoislands explore their energy landscape over time and eventually transition to lower energy states as compared to the frozen-in configurations obtained upon cooling from above the Curie temperature. Thus, this materials system allows for a facile method to systematically study thermal evolution of artificial spin ice arrays of nanoislands at temperatures modestly above room temperature.

Soft x-ray photoemission electron microscopy with an in situ magnetic field has been used to study the relationship between ferromagnetic and antiferromagnetic spin alignment and the switching/reversal field of epitaxial micromagnetic structures. We investigated a model system consisting of a bilayer of ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic LaFeO3 where the spin axes in each layer can be driven from mutually perpendicular (spin-flop) to parallel alignment by varying the temperature between 30 and 300 K. Results show that not only does this spin alignment noticeably influence the bilayer micromagnet coercivity compared to La0.7Sr0.3MnO3 single-layer micromagnets, but the coercivity within this materials system can be tuned over a wide range by careful balance of material properties.

Lithium lanthanum titanate (LLTO) is a promising solid state electrolyte for solid state batteries due to its demonstrated high bulk ionic conductivity. However, crystalline LLTO has a relatively low grain boundary conductivity, limiting the overall material conductivity. In this work, we investigate amorphous LLTO (a-LLTO) thin films grown by pulsed laser deposition (PLD). By controlling the background pressure and temperature we are able to optimize the ionic conductivity to 3 × 10-4 S/cm and electronic conductivity to 5 × 10-11 S/cm. XRD, TEM, and STEM/EELS analysis confirm that the films are amorphous and indicate that oxygen background gas is necessary during the PLD process to decrease the oxygen vacancy concentration, decreasing the electrical conductivity. Amorphous LLTO is deposited onto high voltage LiNi0.5Mn1.5O4 (LNMO) spinel cathode thin films and cycled up to 4.8 V vs. Li showing excellent capacity retention. These results demonstrate that a-LLTO has the potential to be integrated into high voltage thin film batteries.