Tuning the Solvation Structure in Water-Based Solution Enables Surface Reconstruction of Layered Oxide Cathodes toward Long Lifespan Sodium-Ion Batteries.

Layered oxides of sodium-ion batteries suffer from severe side reactions on the electrode/electrolyte interface, leading to fast capacity degradation. Although surface reconstruction strategies are widely used to solve the above issues, the utilization of the low-cost wet chemical method is extremely challenging for moisture-sensitive Na-based oxide materials. Here, the solvation tuning strategy is proposed to overcome the deterioration of NaNi1/3Mn1/3Fe1/3O2 in water-based solution and conduct the surface reconstruction. When capturing the water molecules by the solvation structure of cations, here is Li+, the structural collapse and degradation of layered oxides in water-based solvents are greatly mitigated. Furthermore, Li(H2O)3EA+ promotes the profitable Li+/Na+ exchange to build a robust surface, which hampers the decomposition of electrolytes and the structural evolution upon cycling. Accordingly, the lifespan of Li-reinforced materials is prolonged to three times that of the pristine one. This work represents a step forward in understanding the surface reconstruction operated in a water-based solution for high-performance sodium layered oxide cathodes.

Interfacial Mn Vacancy for Li-Rich Mn-Based Oxide Cathodes.

Apart from the O releasing at a low rate, large polarization at a high rate is also a big challenge for Li-rich Mn-based oxide (LMO). Prussian blue (PB) with a specific redox potential is regarded as a suitable coating layer to overcome these drawbacks, while its stability is easily destroyed by the intrinsic Jahn-Teller effect after a long run. Herein, Mn vacancy (MV) is introduced into the PB coating layer to enhance its stability. Consequently, such an electrode (MV-PB@LMO) presents a prolonged lifespan compared to the electrode with a PB coating layer only. Furthermore, it is found that the electrode with Mn vacancy in LMO (MV@LMO) shows superior reversibility, which displays a boosted activity of LMO. This research exhibits the advanced merits of Mn vacancy for LMO, and further work may pay more attention to strengthening of the stability of MV@LMO.

Controllable Heterojunctions with a Semicoherent Phase Boundary Boosting the Potassium Storage of CoSe2 /FeSe2.

Heterostructure construction is an efficient method for reinforcing K+ storage of transition metal selenides. The spontaneously developed internal electric fields give a strong boost to charge transport and significantly reduce the activation energy. Nevertheless, perfection of the interfacial region based on the energy level gradient and lattice matching degree is still a great challenge. Herein, rich vacancies and ultrafine CoSe2 -FeSe2 heterojunctions with semicoherent phase boundary are simultaneously obtained, which possess unique electronic structures and abundant active sites. When employed as anodes for potassium-ion batteries (PIBs), CoSe2 -FeSe2 @C composites display a reversible potassium storage of 401.1 mAh g-1 at 100 mA g-1 and even 275 mAh g-1 at 2 A g-1 . Theoretical calculation also reveals that the potassium-ion diffusion can be dramatically promoted by the controllable CoSe2 -FeSe2 heterojunction.

ß-FeOOH Interlayer With Abundant Oxygen Vacancy Toward Boosting Catalytic Effect for Lithium Sulfur Batteries.

Due to the shuttle effect and low conductivity of sulfur (S), it has been challenging to realize the application of lithium-sulfur (Li-S) batteries with high performance and long cyclability. In this study, a high catalytic active CNTs@FeOOH composite is introduced as a functional interlayer for Li-S batteries. Interestingly, the existence of oxygen vacancy in FeOOH functions electrocatalyst and promotes the catalytic conversion of intercepted lithium polysulfides (LiPS). As a result, the optimized CNTs@FeOOH interlayer contributed to a high reversible capacity of 556 mAh g-1 at 3,200 mA g-1 over 350 cycles. This study demonstrates that enhanced catalytic effect can accelerate conversion efficiency of polysulfides, which is beneficial of boosting high performance Li-S batteries.

Asynchronous reactions of "self-matrix" dual-crystals effectively accommodating volume expansion/shrinkage of electrode materials with enhanced sodium storage.

The large volume expansion of FeS2 is successfully accommodated via a series of asynchronous redox reactions of dual-crystalline FeS2. Consequently, a durable sodium storage performance with a reversible capacity of 567.7 mA h g-1 is obtained at 0.1 A g-1 after 50 cycles. This novel strategy can also be utilized in other types of electrodes having large volume change upon cycling.

Mesoporous ZnCo2O4/rGO nanocomposites enhancing sodium storage.

In this study, mesoporous ZnCo2O4/rGO nanocomposites were favorably synthesized via a simple solvothermal technique. As a prospective anode material for sodium-ion batteries, the resulting ZnCo2O4/rGO-II nanocomposite exhibited superior electrochemical sodium storage performance with predominant specific capacity, favorable cyclability and ascendant rate capability. For example, an outstanding discharge capacity of 210.5 mAh g-1 was delivered at a current density of 200 mA g-1. Notably, the nanocomposite could yield a discharge capacity of 101.7 mAh g-1 at a current density of 1000 mA g-1 after 500 loops, which certifies its superior capacity retention and predominant cycling stability. The boosted performance of the anode materials is due to the mutual synergistic effect resulting from a combination of the mesoporous ZnCo2O4 nanospheres and conducting reduced graphene oxide nanosheets.

Controllably Designed "Vice-Electrode" Interlayers Harvesting High Performance Lithium Sulfur Batteries.

An interlayer has been regarded as a promising mediator to prolong the life span of lithium sulfur batteries because its excellent absorbability to soluble polysulfide efficiently hinders the shuttle effect. Herein, we designed various interlayers and understand the working mechanism of an interlayer for lithium sulfur batteries in detail. It was found that the electrochemical performance of a S electrode for an interlayer located in cathode side is superior to the pristine one without interlayers. Surprisingly, the performance of the S electrode for an interlayer located in anode side is poorer than that of pristine one. For comparison, glass fibers were also studied as a nonconductive interlayer for lithium sulfur batteries. Unlike the two interlayers above, these nonconductive interlayer did displays significant capacity fading because polysulfides were adsorbed onto insulated interlayer. Thus, the nonconductive interlayer function as a "dead zone" upon cycling. Based on our findings, it was for the first time proposed that a controllably optimized interlayer, with electrical conductivity as well as the absorbability of polysulfides, may function as a "vice-electrode" of the anode or cathode upon cycling. Therefore, the cathodic conductive interlayer can enhance lithium sulfur battery performance, and the anodic conductive interlayer may be helpful for the rational design of 3D networks for the protection of lithium metal.