Reinterpreting the Intercalation-Conversion Mechanism of FeP Anodes in Lithium/Sodium-Ion Batteries from Evolution of the Magnetic Phase.

Batteries with intercalation-conversion-type electrodes tend to achieve high-capacity storage, but the complicated reaction process often suffers from confusing electrochemical mechanisms. Here, we reinterpreted the essential issue about the potential of the conversion reaction and whether there is an intercalation reaction in a lithium/sodium-ion battery (LIB/SIB) with the FeP anode based on the evolution of the magnetic phase. Especially, the ever-present intercalation process in a large voltage range followed by the conversion reaction with extremely low potential was confirmed in FeP LIB, while it is mainly the conversion reaction for the sodium storage mechanism in FeP SIB. The insufficient conversion reaction profoundly limits the actual capacity to the expectedly respectable value. Accordingly, a graphene oxide modification strategy was proposed to increase the reversible capacity of FeP LIB/SIB by 99% and 132%, respectively. The results facilitate the development of anode materials with a high capacity and low operating potential.

Interfacial engineering of Si anodes by confined doping of Co toward high initial coulombic efficiency.

A Si/Si-Co multilayer film, with Co confined doping in the silicon anode, was successfully fabricated by alternating magnetron sputtering, achieving both metal doping and surface coating. Operando magnetometry revealed the stability of the Si-Co layers during cycling. The symmetrical Si-Co layers can protect the overall structure of the Si anodes and facilitate electron conduction. Consequently, the resultant Si anode delivers an impressive initial coulombic efficiency of 93.4% with large capacity retention of 85.07% after 100 cycles.

Revealing the effect of LiOH on forming a SEI using a Co magnetic "probe".

The solid-electrolyte-interphase (SEI) plays a critical role in lithium-ion batteries (LIBs) because of its important influence on electrochemical performance, such as cycle stability, coulombic efficiency, etc. Although LiOH has been recognized as a key component of the SEI, its influence on the SEI and electrochemical performance has not been well clarified due to the difficulty in precisely controlling the LiOH content and characterize the detailed interface reactions. Here, a gradual change of LiOH content is realized by different reduction schemes among Co(OH)2, CoOOH and CoO. With reduced Co nanoparticles as magnetic "probes", SEI characterization is achieved by operando magnetometry. By combining comprehensive characterization and theoretical calculations, it is verified that LiOH leads to a composition transformation from lithium ethylene di-carbonate (LEDC) to lithium ethylene mono-carbonate (LEMC) in the SEI and ultimately results in capacity decay. This work unfolds the detailed SEI reaction scenario involving LiOH, provides new insights into the influence of SEI composition, and has value for the co-development between the electrode materials and electrolyte.

Nanosized MoSe2@Carbon Matrix: A Stable Host Material for the Highly Reversible Storage of Potassium and Aluminum Ions.

Owing to their low cost and abundant reserves relative to conventional lithium-ion batteries (LIBs), potassium-ion batteries (PIBs), and aluminum-ion batteries (AIBs) have shown appealing potential for electrochemical energy storage, but progress so far has been limited by the lack of suitable electrode materials. In this work, we demonstrated a facile strategy to achieve highly reversible potassium and aluminum ions storage in strongly coupled nanosized MoSe2@carbon matrix, induced through an ion complexation strategy. We present a broad range of electrochemical characterization of the synthesized product that exhibits high specific capacities, good rate capability, and excellent cycling stability toward PIBs and AIBs. Through a series of systematic ex situ X-ray photoelectron spectroscopy (XPS) characterizations and density functional theory (DFT) calculations, the Al3+ intercalation mechanism of MoSe2-based AIBs are elucidated. Moreover, both the assembled PIBs and AIBs worked well when exposed to low and high temperatures within the range of -10 to 50 °C, showing promise for energy storage devices in harsh environment. The present study provides new insights into the exploration of MoSe2 as high-performance electrode materials for PIBs and AIBs.