Modern sustainability challenges in recent years have warranted the development of new energy storage technologies. Practical realization of the lithium–O2 battery holds great promise for ...revolutionizing energy storage as it holds the highest theoretical specific energy of any rechargeable battery yet discovered. However, the complete realization of Li–O2 batteries necessitates ambient air operations, which presents quite a few challenges, as carbon dioxide (CO2) and water (H2O) contaminants introduce unwanted byproducts from side reactions that greatly affect battery performance. Although current research has thoroughly explored the beneficial incorporation of CO2, much mystery remains over the inconsistent effects of H2O. The presence of water in both the cathode and electrolyte has been observed to alter reaction mechanisms differently, resulting in a diverse range of effects on voltage, capacity, and cyclability. Moreover, recent preliminary research with catalysts and redox mediators has attempted to utilize the presence of water to the battery's benefit. Here, the key mechanism discrepancies of water‐afflicted Li–O2 batteries are presented, concluding with a perspective on future research directions for nonaqueous Li–O2 batteries.
Water impurities can significantly affect Li–O2 electrochemistry. An overview of recent developments of Li–O2/H2O batteries is presented, aiming at gaining a better understanding of Li–O2/H2O batteries to facilitate future research progress in this emerging field.
Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior ...remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn
O
cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn
O
exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn
O
with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries.
Mechanical integrity issues such as particle cracking are considered one of the leading causes of structural deterioration and limited long-term cycle stability for Ni-rich cathode materials of ...Li-ion batteries. Indeed, the detrimental effects generated from the crack formation are not yet entirely addressed. Here, applying physicochemical and electrochemical ex situ and in situ characterizations, the effect of Co and Mn on the mechanical properties of the Ni-rich material are thoroughly investigated. As a result, we successfully mitigate the particle cracking issue in Ni-rich cathodes via rational concentration gradient design without sacrificing the electrode capacity. Our result reveals that the Co-enriched surface design in Ni-rich particles benefits from its low stiffness, which can effectively suppress the formation of particle cracking. Meanwhile, the Mn-enriched core limits internal expansion and improve structural integrity. The concentration gradient design also promotes morphological stability and cycling performances in Li metal coin cell configuration.
The exceptional electrical, optical, thermal and mechanical properties make graphene and carbon nanotubes (CNTs) promising for a large variety of applications, including energy storage. In practice, ...it is higly important to translator these properties associated with the low‐dimensional carbon nanomaterials into bulk materials/devices. Recent theoretical studies have proven that three‐dimensional (3D) pillared architectures, consisting of parallel graphene layers intercalated by vertically aligned carbon nanotubes (VA‐CNTs) in between, possess desriable transport and mechanical properties in all dimensions while maintaining the excellent properties of their building blocks. However, it remains challenging to experimentally realize such 3D pillared graphene/VA‐CNT hybrids. Here, tunable 3D pillared graphene/VA‐CNT architectures are formed by chemical vapor deposition, and a template‐free contact transfer process is presented, involving the hydrophobic‐hydrophobic interactions between graphene and VA‐CNTs. The resultant 3D graphene/VA‐CNT hybrids are demonstrated to be efficient electrode materials for supercapacitors with good performance. This newly‐developed methodology holds great potential for fabricating various 3D architectures with many other materials for a wide range of multifunctional applications, including energy storage, electrical and thermal managements, and flexible electronics.
3D pillared graphene/vertically aligned carbon nanotube (VA‐CNT) architectures are constructed by a facile yet versatile layer‐by‐layer transfer technique. Supercapacitors based on the newly developed graphene/VA‐CNT hybrid electrode show promising performance.
Abstract
High-energy density lithium-rich layered oxides are among the most promising candidates for next-generation energy storage. Unfortunately, these materials suffer from severe electrochemical ...degradation that includes capacity loss and voltage decay during long-term cycling. Present research efforts are primarily focused on understanding voltage decay phenomena while origins for capacity degradation have been largely ignored. Here, we thoroughly investigate causes for electrochemical performance decline with an emphasis on capacity loss in the lithium-rich layered oxides, as well as reaction pathways and kinetics. Advanced synchrotron-based X-ray two-dimensional and three-dimensional imaging techniques are combined with spectroscopic and scattering techniques to spatially visualize the reactivity at multiple length-scales on lithium- and manganese-rich layered oxides. These methods provide direct evidence for inhomogeneous manganese reactivity and ionic nickel rearrangement. Coupling deactivated manganese with nickel migration provides sluggish reaction kinetics and induces serious structural instability in the material. Our findings provide new insights and further understanding of electrochemical degradation, which serve to facilitate cathode material design improvements.
The need for high-energy batteries has driven the development of binder-free electrode architectures. However, the weak bonding between the electrode particles and the current collector cannot ...withstand the severe volume change of active materials upon battery cycling, which largely limit the large-scale application of such electrodes. Using tin nanoarrays electrochemically deposited on copper substrate as an example, here we demonstrate a strategy of strengthening the connection between electrode and current collector by thermally alloying tin and copper at their interface. The locally formed tin-copper alloys are electron-conductive and meanwhile electrochemically inactive, working as an ideal "glue" robustly bridging tin and copper to survive harsh cycling conditions in sodium ion batteries. The working mechanism of the alloy "glue" is further characterized through a combination of electrochemical impedance spectroscopy, atomic structural analysis and in situ X-ray diffraction, presenting itself as a promising strategy for engineering binder-free electrode with endurable performance.
Recent works into sulfide-type solid electrolyte materials have attracted much attention among the battery community. Specifically, the oxidative decomposition of phosphorus and sulfur based solid ...state electrolyte has been considered one of the main hurdles towards practical application. Here we demonstrate that this phenomenon can be leveraged when lithium thiophosphate is applied as an electrochemically "switched-on" functional redox mediator-generator for the activation of commercial bulk lithium sulfide at up to 70 wt.% lithium sulfide electrode content. X-ray adsorption near-edge spectroscopy coupled with electrochemical impedance spectroscopy and Raman indicate a catalytic effect of generated redox mediators on the first charge of lithium sulfide. In contrast to pre-solvated redox mediator species, this design decouples the lithium sulfide activation process from the constraints of low electrolyte content cell operation stemming from pre-solvated redox mediators. Reasonable performance is demonstrated at strict testing conditions.
Flow-based hydrovoltaic nanogenerators have attracted particular attention as efficient and facile miniature energy-harvesting devices. However, they deliver relatively low output power density and ...limited power conversion efficiency owing to inefficient charge separation and poor charge accumulation. Here, we report the fabrication of high-performance, fiber-shaped fluidic nanogenerators (FFNGs) that use MoS2-encapsulated C fibers. The FFNGs deliver stable output voltages of 540 mV and an ultrahigh power density of 10.8 W m−2. With experiments and density functional theory calculations, improvements in output performance can be attributed to smaller energy requirements for Na+ cation adsorption, increased charge separation, and diffusion layer formations on the near surface. Moreover, self-powered, integrated devices achieve a maximum total power conversion-storage efficiency of ∼11% and stable output voltage up to 3.1 V, which is applicable for use in consumer electronics devices.
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Fiber-shaped fluidic nanogenerators assembled from MoS2-encapsulated C fibersA power density of 10.8 W m−2 with output voltage of 540 mV can be achievedThis is due to small adsorption energy of Na+ and effective charge separationThe device achieves a power conversion-storage efficiency of up to ∼11%
Hydrovoltaic nanogenerators are interesting as miniature devices for harvesting energy from flowing water. Yang et al. report a fiber-shaped fluidic nanogenerator based on MoS2-encapsulated C fibers with ultrahigh power density and energy conversion efficiency.
An ordered partition of n={1,2,…,n} is a partition whose blocks are endowed with a linear order. Let OPn,k be the set of ordered partitions of n with k blocks and OPn,k(σ) be the set of ordered ...partitions in OPn,k that avoid a pattern σ. For any permutation pattern σ of length three, Godbole, Goyt, Herdan and Pudwell obtained formulas for the number of ordered partitions of n with 3 blocks avoiding σ as well as the number of ordered partitions of n with n−1 blocks avoiding σ. They also showed that |OPn,k(σ)|=|OPn,k(123)| for any permutation σ of length 3. Moreover, they raised a question concerning the enumeration of OPn,k(123), and conjectured that the number of ordered partitions of 2n with n blocks of size 2 avoiding σ satisfies a second order linear recurrence relation. In answer to the question of Godbole, et al., we establish a connection between |OPn,k(123)| and the number en,d of 123-avoiding permutations of n with d descents. Using the bivariate generating function of en,d given by Barnabei, Bonetti and Silimbani, we obtain the bivariate generating function of |OPn,k(123)|. Meanwhile, we confirm the conjecture of Godbole, et al. by deriving the generating function for the number of 123-avoiding ordered partitions of 2n with n blocks of size 2.
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