Fast-charging and high-energy-density batteries pose significant safety concerns due to high rates of heat generation. Understanding how localized high temperatures affect the battery is critical but ...remains challenging, mainly due to the difficulty of probing battery internal temperature with high spatial resolution. Here we introduce a method to induce and sense localized high temperature inside a lithium battery using micro-Raman spectroscopy. We discover that temperature hotspots can induce significant lithium metal growth as compared to the surrounding lower temperature area due to the locally enhanced surface exchange current density. More importantly, localized high temperature can be one of the factors to cause battery internal shorting, which further elevates the temperature and increases the risk of thermal runaway. This work provides important insights on the effects of heterogeneous temperatures within batteries and aids the development of safer batteries, thermal management schemes, and diagnostic tools.
Although liquid-solid interfaces are foundational in broad areas of science, characterizing this delicate interface remains inherently difficult because of shortcomings in existing tools to access ...liquid and solid phases simultaneously at the nanoscale. This leads to substantial gaps in our understanding of the structure and chemistry of key interfaces in battery systems. We adopt and modify a thin film vitrification method to preserve the sensitive yet critical interfaces in batteries at native liquid electrolyte environments to enable cryo–electron microscopy and spectroscopy. We report substantial swelling of the solid-electrolyte interphase (SEI) on lithium metal anode in various electrolytes. The swelling behavior is dependent on electrolyte chemistry and is highly correlated to battery performance. Higher degrees of SEI swelling tend to exhibit poor electrochemical cycling.
It has recently been shown that sulfur, a solid material in its elementary form S
, can stay in a supercooled state as liquid sulfur in an electrochemical cell. We establish that this newly ...discovered state could have implications for lithium-sulfur batteries. Here, through in situ studies of electrochemical sulfur generation, we show that liquid (supercooled) and solid elementary sulfur possess very different areal capacities over the same charging period. To control the physical state of sulfur, we studied its growth on two-dimensional layered materials. We found that on the basal plane, only liquid sulfur accumulates; by contrast, at the edge sites, liquid sulfur accumulates if the thickness of the two-dimensional material is small, whereas solid sulfur nucleates if the thickness is large (tens of nanometres). Correlating the sulfur states with their respective areal capacities, as well as controlling the growth of sulfur on two-dimensional materials, could provide insights for the design of future lithium-sulfur batteries.
Abstract
Fast-charging is considered as one of the most desired features needed for lithium-ion batteries to accelerate the mainstream adoption of electric vehicles. However, current battery charging ...protocols mainly consist of conservative rate steps to avoid potential hazardous lithium plating and its associated parasitic reactions. A highly sensitive onboard detection method could enable battery fast-charging without reaching the lithium plating regime. Here, we demonstrate a novel differential pressure sensing method to precisely detect the lithium plating event. By measuring the real-time change of cell pressure per unit of charge (dP/dQ) and comparing it with the threshold defined by the maximum of dP/dQ during lithium-ion intercalation into the negative electrode, the onset of lithium plating before its extensive growth can be detected with high precision. In addition, we show that by integrating this differential pressure sensing into the battery management system (BMS), a dynamic self-regulated charging protocol can be realized to effectively extinguish the lithium plating triggered by low temperature (0 °C) while the conventional static charging protocol leads to catastrophic lithium plating at the same condition. We propose that differential pressure sensing could serve as an early nondestructive diagnosis method to guide the development of fast-charging battery technologies.
Lithium (Li) metal is the ultimate anode material for Li batteries because of its highest capacity among all candidates. Recent research has focused on stable interphase and host materials to address ...its low stability and reversibility. Here, we discover that tortuosity is a critical parameter affecting the morphology and electrochemical performances of hosted Li anodes. In three types of hosts—vertically aligned, horizontally aligned, and random reduced graphene oxide (rGO) electrodes with tortuosities of 1.25, 4.46, and 1.76, respectively—we show that high electrode tortuosity causes locally higher current density on the top surface of electrodes, resulting in thick Li deposition on the surface and degraded cycling performance. Low electrode tortuosity in the vertically aligned rGO host enables homogeneous Li transport and uniform Li deposition across the host, realizing greatly improved cycling stability. Using this principle of low tortuosity, the designed electrode shows through-electrode uniform morphology with anodic Coulombic efficiency of ∼99.1% under high current and capacity cycling conditions.
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•Controllable alignment and tortuosity in Li-metal host•Low tortuosity mitigates locally enhanced concentration gradient and current density•Suppress uneven Li dendrite overgrowth on top surface by decreasing host tortuosity•Strong correlation between host tortuosity and reversibility of hosted Li-metal anode
Host electrodes, such as three-dimensional (3D) porous carbon matrices, can accommodate the relative infinite volume change and decrease the local current density for mitigating dendritic growth and reversibility issues in a Li-metal anode. However, a preferential Li accumulation on the upper surface of the host is commonly observed during cycling, which has not been rationalized or addressed. Here, we show that the host tortuosity, as a complexity of the microstructure inside the 3D host, is responsible for this uneven Li distribution. In comparisons between rGO hosts with different tortuosities, the locally enhanced current density and concentration gradient showed a strong correlation with high host tortuosity, leading to top-surface accumulation of Li dendrites and a blocked ion-transport pathway. When the host tortuosity was reduced from 4.46 to 1.25, rGO hosts exhibited a doubled cycle life in full cells with high uniformity within the anode, suggesting the importance of this tortuosity parameter for stable Li-metal batteries.
A strong correlation between host tortuosity and cycling reversibility of a hosted Li-metal anode is revealed for the first time. High tortuosity leads to preferential top-surface Li deposition based on locally enhanced current density and concentration gradient. This top-surface accumulated Li blocks inward ion transport and invalidates the internal electrode, further aggravating the uneven current distribution and non-uniform plating and stripping. Decreased electrode tortuosity can significantly improve the anodic Coulombic efficiency, uniformity of Li-metal stripping and plating, and cycling stability of the rGO host.
Designing materials with ultralow thermal conductivity has broad technological impact, from thermal protection to energy harvesting. Low thermal conductivity is commonly observed in anharmonic and ...strongly disordered materials, yet a microscopic understanding of the correlation to atomic motion is often lacking. Here we report that molecular insertion into an existing two-dimensional layered lattice structure creates a hybrid superlattice with extremely low thermal conductivity. Vibrational characterization and ab initio molecular dynamics simulations reveal strong damping of transverse acoustic waves and significant softening of longitudinal vibrations. Together with spectral correlation analysis, we demonstrate that the molecular insertion creates liquid-like atomic motion in the existing lattice framework, causing a large suppression of heat conduction. The hybrid materials can be transformed into solution-processable coatings and used for thermal protection in wearable electronics. Our work provides a generic mechanism for the design of heat insulators and may further facilitate the engineering of heat conduction based on understanding atomic correlations.
Charge density waves spontaneously breaking lattice symmetry through periodic lattice distortion, and electron–electron and electron–phonon interactions, can lead to a new type of electronic band ...structure. Bulk 2H-TaS2 is an archetypal transition metal dichalcogenide supporting charge density waves with a phase transition at 75 K. Here, it is shown that charge density waves can exist in exfoliated monolayer 2H-TaS2 and the transition temperature can reach 140 K, which is much higher than that in the bulk. The degenerate breathing and wiggle modes of 2H-TaS2 originating from the periodic lattice distortion are probed by optical methods. The results open an avenue to investigating charge density wave phases in two-dimensional transition metal dichalcogenides and will be helpful for understanding and designing devices based on charge density waves.
Lithium–sulfur (Li–S) batteries are promising next-generation energy storage technologies due to their high theoretical energy density, environmental friendliness, and low cost. However, low ...conductivity of sulfur species, dissolution of polysulfides, poor conversion from sulfur reduction, and lithium sulfide (Li2S) oxidation reactions during discharge–charge processes hinder their practical applications. Herein, under the guidance of density functional theory calculations, we have successfully synthesized large-scale single atom vanadium catalysts seeded on graphene to achieve high sulfur content (80 wt % sulfur), fast kinetic (a capacity of 645 mAh g–1 at 3 C rate), and long-life Li–S batteries. Both forward (sulfur reduction) and reverse reactions (Li2S oxidation) are significantly improved by the single atom catalysts. This finding is confirmed by experimental results and consistent with theoretical calculations. The ability of single metal atoms to effectively trap the dissolved lithium polysulfides (LiPSs) and catalytically convert the LiPSs/Li2S during cycling significantly improved sulfur utilization, rate capability, and cycling life. Our work demonstrates an efficient design pathway for single atom catalysts and provides solutions for the development of high energy/power density Li–S batteries.
The increasing demand for next-generation energy storage systems necessitates the development of high-performance lithium batteries
. Unfortunately, current Li anodes exhibit rapid capacity decay and ...a short cycle life
, owing to the continuous generation of solid electrolyte interface
and isolated Li (i-Li)
. The formation of i-Li during the nonuniform dissolution of Li dendrites
leads to a substantial capacity loss in lithium batteries under most testing conditions
. Because i-Li loses electrical connection with the current collector, it has been considered electrochemically inactive or 'dead' in batteries
. Contradicting this commonly accepted presumption, here we show that i-Li is highly responsive to battery operations, owing to its dynamic polarization to the electric field in the electrolyte. Simultaneous Li deposition and dissolution occurs on two ends of the i-Li, leading to its spatial progression toward the cathode (anode) during charge (discharge). Revealed by our simulation results, the progression rate of i-Li is mainly affected by its length, orientation and the applied current density. Moreover, we successfully demonstrate the recovery of i-Li in Cu-Li cells with >100% Coulombic efficiency and realize LiNi
Mn
Co
O
(NMC)-Li full cells with extended cycle life.
The doping or the alteration of crystals with guest species to obtain desired properties has long been a research frontier in materials science. However, the closely packed lattice structure in many ...crystals has limited the applicability of this strategy. The advent of 2D layered materials has led to revitalized interest in utilizing this approach through two important strategies, gating and intercalation, offering reversible modulation of the properties of the host material without breaking chemical bonds. In addition, these dynamically tunable techniques have enabled the synthesis of new hybrid materials. Here, we review how interactions between guest species and host 2D materials can tune the physics and chemistry of materials and discuss their remarkable potential for creating artificial materials and architectures beyond the reach of conventional methods.Introduction of guest species into archetype materials lays out a foundational pathway for creating new materials classes with desired functionalities. This Review discusses two main strategies of such applied to 2D layered materials: gating, where the guest species rest on the surface, and intercalation, where the guest species are incorporated into the host lattice.
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