A fast-charging/discharging and long-term stable artificial electrode enabled by space charge storage mechanism.

Lithium-ion batteries with fast-charging/discharging properties are urgently needed for the mass adoption of electric vehicles. Here, we show that fast charging/discharging, long-term stable and high energy charge-storage properties can be realized in an artificial electrode made from a mixed electronic/ionic conductor material (Fe/LixM, where M = O, F, S, N) enabled by a space charge principle. Particularly, the Fe/Li2O electrode is able to be charged/discharged to 126 mAh g-1 in 6 s at a high current density of up to 50 A g-1, and it also shows stable cycling performance for 30,000 cycles at a current density of 10 A g-1, with a mass-loading of ~2.5 mg cm-2 of the electrode materials. This study demonstrates the critical role of the space charge storage mechanism in advancing electrochemical energy storage and provides an unconventional perspective for designing high-performance anode materials for lithium-ion batteries.

Real-time tracking of electron transfer at catalytically active interfaces in lithium-ion batteries.

Transition metals and related compounds are known to exhibit high catalytic activities in various electrochemical reactions thanks to their intriguing electronic structures. What is lesser known is their unique role in storing and transferring electrons in battery electrodes which undergo additional solid-state conversion reactions and exhibit substantially large extra capacities. Here, a full dynamic picture depicting the generation and evolution of electrochemical interfaces in the presence of metallic nanoparticles is revealed in a model CoCO3/Li battery via an in situ magnetometry technique. Beyond the conventional reduction to a Li2CO3/Co mixture under battery operation, further decomposition of Li2CO3 is realized by releasing interfacially stored electrons from its adjacent Co nanoparticles, whose subtle variation in the electronic structure during this charge transfer process has been monitored in real time. The findings in this work may not only inspire future development of advanced electrode materials for next-generation energy storage devices but also open up opportunities in achieving in situ monitoring of important electrocatalytic processes in many energy conversion and storage systems.

Electrochemical interfacial catalysis in Co-based battery electrodes involving spin-polarized electron transfer.

Interfacial catalysis occurs ubiquitously in electrochemical systems, such as batteries, fuel cells, and photocatalytic devices. Frequently, in such a system, the electrode material evolves dynamically at different operating voltages, and this electrochemically driven transformation usually dictates the catalytic reactivity of the material and ultimately the electrochemical performance of the device. Despite the importance of the process, comprehension of the underlying structural and compositional evolutions of the electrode material with direct visualization and quantification is still a significant challenge. In this work, we demonstrate a protocol for studying the dynamic evolution of the electrode material under electrochemical processes by integrating microscopic and spectroscopic analyses, operando magnetometry techniques, and density functional theory calculations. The presented methodology provides a real-time picture of the chemical, physical, and electronic structures of the material and its link to the electrochemical performance. Using Co(OH)2 as a prototype battery electrode and by monitoring the Co metal center under different applied voltages, we show that before a well-known catalytic reaction proceeds, an interfacial storage process occurs at the metallic Co nanoparticles/LiOH interface due to injection of spin-polarized electrons. Subsequently, the metallic Co nanoparticles act as catalytic activation centers and promote LiOH decomposition by transferring these interfacially residing electrons. Most intriguingly, at the LiOH decomposition potential, electronic structure of the metallic Co nanoparticles involving spin-polarized electrons transfer has been shown to exhibit a dynamic variation. This work illustrates a viable approach to access key information inside interfacial catalytic processes and provides useful insights in controlling complex interfaces for wide-ranging electrochemical systems.

Fe2(MoO4)3 assembled by cross-stacking of porous nanosheets enables a high-performance aluminum-ion battery.

Rechargeable aluminum-ion batteries have attracted increasing attention owing to the advantageous multivalent ion storage mechanism thus high theoretical capacity as well as inherent safety and low cost of using aluminum. However, their development has been largely impeded by the lack of suitable positive electrodes to provide both sufficient energy density and satisfactory rate capability. Here we report a candidate positive electrode based on ternary metal oxides, Fe2(MoO4)3, which was assembled by cross-stacking of porous nanosheets, featuring superior rate performance and cycle stability, and most importantly a well-defined discharge voltage plateau near 1.9 V. Specifically, the positive electrode is able to deliver reversible capacities of 239.3 mA h g-1 at 0.2 A g-1 and 73.4 mA h g-1 at 8.0 A g-1, and retains 126.5 mA h g-1 at 1.0 A g-1 impressively, after 2000 cycles. Furthermore, the aluminum-storage mechanism operating on Al3+ intercalation in this positive electrode is demonstrated for the first time via combined in situ and ex situ characterization studies and density functional theory calculations. This work not only explores potential positive electrodes for aluminum-based batteries but also sheds light on the fundamental charge storage mechanism within the electrode.

Revealing An Intercalation-Conversion-Heterogeneity Hybrid Lithium-Ion Storage Mechanism in Transition Metal Nitrides Electrodes with Jointly Fast Charging Capability and High Energy Output.

The performance of electrode materials depends intensively on the lithium (Li)-ion storage mechanisms correlating ultimately with the Coulombic efficiency, reversible capacity, and morphology variation of electrode material upon cycling. Transition metal nitrides anode materials have exhibited high-energy density and superior rate capability; however, the intrinsic mechanism is largely unexplored and still unclear. Here, a typical 3D porous Fe2 N micro-coral anode is prepared and, an intercalation-conversion-heterogeneity hybrid Li-ion storage mechanism that is beyond the conventional intercalation or conversion reaction is revealed through various characterization techniques and thermodynamic analysis. Interestingly, using advanced in situ magnetometry, the ratio (ca. 24.4%) of the part where conversion reaction occurs to the entire Fe2 N can further be quantified. By rationally constructing a Li-ion capacitor comprising 3D porous Fe2 N micro-corals anode and commercial AC cathode, the hybrid full device delivers a high energy-density (157 Wh kg-1 ) and high power-density (20 000 W kg-1 ), as well as outstanding cycling stability (93.5% capacitance retention after 5000 cycles). This research provides an original and insightful method to confirm the reaction mechanism of material related to transition metals and a fundamental basis for emerging fast charging electrode materials to be efficiently explored for a next-generation battery.

Long life exceeding 10 000 cycles for aluminum-ion batteries based on an FeTe2@GO composite as the cathode.

A nanocomposite consisting of iron telluride wrapped with graphene oxide (GO) was prepared via a hydrothermal method. As the cathode material for aluminum-ion batteries (AIBs), it exhibited a remarkable long-term cycle performance with a reversible capacity of 120.4 mA h g-1 at 1 A g-1 after 10 000 cycles, i.e., a cyclability better than those of all other transition metal chalcogenides in AIBs reported to date. Furthermore, an energy storage mechanism, involving the intercalation and deintercalation of multiple ions (AlCl4-, Cl- and Al3+), was elucidated. This study offers guidance for further development of transition metal tellurides for AIBs.

Novel Bimetallic Activated Center Alloying Mechanism Positive Electrodes for Aluminum Storage.

Aluminum is the most abundant metal element in the Earth's crust, thus developing the rechargeable aluminum-ion batteries (AIBs) provides an ideal opportunity to realize cells with pleasing energy-to-price ratios. However, the further development of AIBs is plagued by the scarcity of suitable positive electrode materials. Here, for the first time, a tin-based alloy positive electrode material for AIBs, Co3 Sn2 wrapped with graphene oxide (Co3 Sn2 @GO composite) is well-designed and investigated to understand the aluminum storage behavior. A series of experimental measurements and theoretical calculations results reveal that a novel "bimetallic activated center alloying reaction" aluminum storage mechanism is occurred on the prepared Co3 Sn2 positive electrode. The reversible alloying/de-alloying process in AlCl3 /[EMIm]Cl ionic liquid, where both Co and Sn in Co3 Sn2 alloys react electrochemically with Al3+ to form Alx Sn and Aly Co is first put forward. This study delineates new insights on the aluminum storage mechanism, which may guide to ultimately exploit the energy benefits of "bimetallic activated center alloying redox".

Operando Magnetometry Probing the Charge Storage Mechanism of CoO Lithium-Ion Batteries.

Cobalt oxide (CoO) is a promising electrode for high-energy-density Li-ion batteries (LIBs), where the charge storage is believed to take place solely during the electrochemical oxidation/reduction processes. However, this simple picture has been increasingly challenged by reported anomalously large storage capacities, indicating the existence of undiscovered extra charge reservoirs inside the system. Here, an advanced operando magnetometry technology is employed to monitor the magnetization variation of the CoO LIBs in real time and, in this particular system, it is clearly demonstrated that the anomalous capacity is associated with both the reversible formation of a spin capacitor and the growth of a polymeric film at low voltages. Furthermore, operando magnetometry provides direct evidence of the catalytic role of metallic Co in assisting the polymeric film formation. These critical findings help pave the way for better understanding of the charge storage mechanisms of transition-metal oxides and further utilizing them to design novel electrode materials.