Phase Control on Surface for the Stabilization of High Energy Cathode Materials of Lithium Ion Batteries.

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi0.5Mn1.5O4 as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries

Vacancy-induced sodium-ion storage in N-doped carbon Nanofiber@MoS2nanosheet arrays

As a promising material for sodium-ion batteries, molybdenum disulphide (MoS2) affords excellent electrochemical performance owing to its large surface area and the accelerated electron transport within individual layers. However, it suffers from slow reaction kinetics and agglomeration owing to low conductivity and high surface energy. In this work, nitrogen-doped carbon nanofiber@MoS2nanosheets arrays with S-vacancies (NC@MoS2-VS) are developed via a process involving electrospining, hydrothermal and annealing. When served as an anode material for SIBs, this material displays a superior capacity of 495 mAh g−1over 100 charge/discharge cycles at a current density of 100 mA g−1, and the pseudocapacitive contribution is up to 74.4% as revealed by the cyclic voltammogram (CV) at 1 mV s−1. The theoretical calculations show that the presence of sulfur vacancies facilitates the adsorption of Na+and enhances the conductivity of MoS2. This work may pave a new avenue to develop other types of metal sulfides for high-performance SIBs

Molybdenum and tungsten chalcogenides for lithium/sodium-ion batteries: Beyond MoS2

Molybdenum and tungsten chalcogenides have attracted tremendous attention in energy storage and conversion due to their outstanding physicochemical and electrochemical properties. There are intensive studies on molybdenum and tungsten chalcogenides for energy storage and conversion, however, there is no systematic review on the applications of WS2, MoSe2and WSe2as anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), except MoS2. Considering the importance of these contents, it is extremely necessary to overview the recent development of novel layered WS2, MoSe2and WSe2beyond MoS2in energy storage. Here, we will systematically overview the recent progress of WS2, MoSe2and WSe2as anode materials in LIBs and SIBs. This review will also discuss the opportunities, and perspectives of these materials in the energy storage fields

Fe-doped phosphorene for the nitrogen reduction reaction

The nitrogen-to-ammonia conversion is one of the most important and challenging processes in chemistry. We have employed spin-polarized density functional theory to propose Fe-doped monolayer phosphorene (Fe-P) as a new catalyst for the N2reduction reaction at room temperature. Our results show that single-atom Fe is the active site, cooperating with P to activate the inert N-N triple bond and reduce N2to NH3via three reliable pathways. Our findings provide a new avenue for single atom catalytic nitrogen fixation under ambient conditions

Zn-Doped Cu(100) facet with efficient catalytic ability for the CO2 electroreduction to ethylene

Electrochemically converting CO2 into fuels and chemicals is an appealing strategy to create energy rich products. The highly demanded product ethylene has been preferably produced on Cu-based catalysts with abundant exposed Cu(100) facets. However, the performance is still limited by the large energy barrier for the C-C dimerization. Here, to lower the energy barrier, we tailor the electronic structure of Cu(100) by doping a series of transition metals using the density functional theory (DFT) method. The zinc-doped Cu(100) surface has shown a superior catalytic performance. Mechanistic study further reveals that doping with Zn alters the electronic structure around Cu, adjusts the atomic arrangement in the active sites and makes the catalyst surface electronegative, which is conducive to the activation of acidic molecular CO2 and the reduction of the energy barrier for C-C dimerization. This work reveals that the doping of Cu with transition metals has great potential in promoting the electrochemical CO2-to-C2H4 conversion. This work also provides deep insights into the formation mechanisms of C2H4, thus guiding the design of Cu-based bimetallic catalysts for its effective production

Electrochemical CO2 reduction over nitrogen-doped SnO2 crystal surfaces

Crystal planes of a catalyst play crucial role in determining the electrocatalytic performance for CO2reduction. The catalyst SnO2can convert CO2molecules into valuable formic acid (HCOOH). Incorporating heteroatom N into SnO2further improves its catalytic activity. To understand the mechanism and realize a highly efficient CO2-to-HCOOH conversion, we used density functional theory (DFT) to calculate the free energy of CO2reduction reactions (CO2RR) on different crystal planes of N-doped SnO2(N-SnO2). The results indicate that N-SnO2lowered the activation energy of intermediates leading to a better catalytic performance than pure SnO2. We also discovered that the N-SnO2(211) plane possesses the most suitable free energy during the reduction process, exhibiting the best catalytic ability for the CO2-to-HCOOH conversion. The intermediate of CO2RR on N-SnO2is HCOO* or COOH* instead of OCHO*. These results may provide useful insights into the mechanism of CO2RR, and promote the development of heteroatom-doped catalyst for efficient CO2RR

Chevrel Phase Mo6T8 (T = S, Se) as Electrodes for Advanced Energy Storage

With the large-scale applications of electric vehicles in recent years, future batteries are required to be higher in power and possess higher energy densities, be more environmental friendly, and have longer cycling life, lower cost, and greater safety than current batteries. Therefore, to develop alternative electrode materials for advanced batteries is an important research direction. Recently, the Chevrel phase Mo 6 T 8 (T = S, Se) has attracted increasing attention as electrode candidate for advanced batteries, including monovalent (e.g., lithium and sodium) and multivalent (e.g., magnesium, zinc and aluminum) ion batteries. Benefiting from its unique open crystal structure, the Chevrel phase Mo 6 T 8 cannot only ensure rapid ion transport, but also retain the structure stability during electrochemical reactions. Although the history of the research on Mo 6 T 8 as electrodes for advanced batteries is short, there has been significant progress on the design and fabrication of Mo 6 T 8 for various advanced batteries as above mentioned. An overview of the recent progress on Mo 6 T 8 electrodes applied in advanced batteries is provided, including synthesis methods and diverse structures for Mo 6 T 8 , and electrochemical mechanism and performance of Mo 6 T 8 . Additionally, a briefly conclusion on the significant progress, obvious drawbacks, emerging challenges and some perspectives on the research of Mo 6 T 8 for advanced batteries in the near future is provided

A cathode for Li-ion batteries made of vanadium oxide on vertically aligned carbon nanotube arrays/graphene foam

A hierarchically structured free-standing V2O5/vertically aligned carbon nanotube/graphene foam (V2O5-VA-CNTs/GF) coated by PEDOT was designed. Instead of forming a thick coating layer around, the V2O5 nanobelts disperse uniformly among the CNTs forest without severe aggregations. The PEDOT-V2O5-VA-CNTs/GF delivered a reversible capacity of 296.8 mAh g−1 at 1C, and has capacity retention of 113.3 mAh g−1 at 5C after 1000 cycles. First principles calculations indicate the addition of VA-CNTs to V2O5 electrode could improve the electronic conductivity and facilitate Li-ion adsorption, which lead to the outstanding Li-ion storage and conversion behaviour

Recent Progress in Graphite Intercalation Compounds for Rechargeable Metal (Li, Na, K, Al)-Ion Batteries

Lithium-ion batteries (LIBs) with higher energy density are very necessary to meet the increasing demand for devices with better performance. With the commercial success of lithiated graphite, other graphite intercalation compounds (GICs) have also been intensively reported, not only for LIBs, but also for other metal (Na, K, Al) ion batteries. In this Progress Report, we briefly review the application of GICs as anodes and cathodes in metal (Li, Na, K, Al) ion batteries. After a brief introduction on the development history of GICs, the electrochemistry of cationic GICs and anionic GICs is summarized. We further briefly summarize the use of cationic GICs and anionic GICs in alkali ion batteries and the use of anionic GICs in aluminium-ion batteries. Finally, we reach some conclusions on the drawbacks, major progress, emerging challenges, and some perspectives on the development of GICs for metal (Li, Na, K, Al) ion batteries. Further development of GICs for metal (Li, Na, K, Al) ion batteries is not only a strong supplement to the commercialized success of lithiated-graphite for LIBs, but also an effective strategy to develop diverse high-energy batteries for stationary energy storage in the future