Addressing cation mixing in layered structured cathodes for lithium-ion batteries:A critical review

High-performance lithium-ion batteries(LIB)are important in powering emerging technologies.Cathodes are regarded as the bottleneck of increasing battery energy density,among which layered oxides are the most promising candidates for LIB.However,a limitation with layered oxides cathodes is the transition metal and Li site mixing,which significantly impacts battery capacity and cycling stability.Despite recent research on Li/Ni mixing,there is a lack of comprehensive understanding of the origin of cation mixing between the transition metal and Li;therefore,practical means to address it.Here,a critical review of cation mixing in layered cathodes has been provided,emphasising the understanding of cation mixing mechanisms and their impact on cathode material design.We list and compare advanced characterisation techniques to detect cation mixing in the material structure;examine methods to regulate the degree of cation mixing in layered oxides to boost battery capacity and cycling performance,and critically assess how these can be applied practically.An appraisal of future research directions,including superexchange interaction to stabilise structures and boost capacity retention has also been concluded.Findings will be of immediate benefit in the design of layered cathodes for high-performance rechargeable LIB and,therefore,of interest to researchers and manufacturers.

Understanding voltage hysteresis and decay during anionic redox reaction in layered transition metal oxide cathodes:A critical review

The emergence of anionic redox reactions in layered transition metal oxide cathodes provides practical opportunity to boost the energy density of rechargeable batteries.However,the activation of anionic redox reaction in layered oxides has significant voltage hysteresis and decay that reduce battery performance and limit commercialization.Here,we critically review the up-todate development of anionic redox reaction in layered oxide cathodes,summarize the proposed reaction mechanism,and unveil their connection to voltage hysteresis and decay based on the state-of-the-art progress.In addition,advances associated with various modification approaches to mitigate the voltage hysteresis/decay in layered transition metal oxide cathodes are also included.Finally,we conclude with an appraisal of further research directions including rational design of high-performance layered oxide cathodes with reversible anionic redox reactions and suppressed voltage hysteresis/decay.Findings will be of immediate benefit to the development of layered oxide cathodes for high performance rechargeable batteries.

Sodium-rich NASICON-structured cathodes for boosting the energy density and lifespan of sodium-free-anode sodium metal batteries

Rechargeable sodium metal batteries(SMBs)have emerged as promising alternatives to commercial Li-ion batteries because of the natural abundance and low cost of sodium resources.However,the overuse of metallic sodium in conventional SMBs limits their energy densities and leads to severe safety concerns.Herein,we propose a sodium-free-anode SMB(SFA-SMB)configuration consisting of a sodium-rich Na superionic conductor-structured cathode and a bare Al/C current collector to address the above challenges.Sodiated Na_(3)V_(2)(PO_(4))_(3)in the form of Na_(5)V_(2)(PO_(4))_(3)was investigated as a cathode to provide a stable and controllable sodium source in the SFA-SMB.It provides not only remarkable Coulombic efficiencies of Na plating/stripping cycles but also a highly reversible three-electron redox reaction within 1.0–3.8 V versus Na/Na+confirmed by structural/electrochemical measurements.Consequently,an ultrahigh energy density of 400 Wh kg^(-1)was achieved for the SFA-SMB with fast Na storage kinetics and impressive capacity retention of 93%after 130 cycles.A narrowed voltage window(3.0–3.8 V vs.Na/Na+)further increased the lifespan to over 300 cycles with a high retained specific energy of 320 Wh kg^(-1).Therefore,the proposed SFA-SMB configuration opens a new avenue for fabricating next-generation batteries with high energy densities and long lifetimes.

A combination of hierarchical pore and buffering layer construction for ultrastable nanocluster Si/SiO_(x)anode

Porous Si can be synthesized from diverse silica(SiO_(2))via magnesiothermic reduction technology and widely employed as potential anode material in lithium ion batteries.However,concerns regarding the influence of residual silicon oxide(SiO_(x))component on resulted Si anode after reduction are still lacked.In this work,we intentionally fabricate a cauliflower-like silicon/silicon oxide(CF-Si/SiO_(x))particles from highly porous SiO_(2)spheres through insufficient magnesiothermic reduction,where residual SiO_(x)component and internal space play an important role in preventing the structural deformation of secondary bulk and restraining the expansion of Si phase.Moreover,the hierarchically structured CF-Si/SiO_(x)exhibits uniformly-dispersed channels,which can improve ion transport and accommodate large volume expansion,simultaneously.As a result,the CF-Si/SiO_(x)-700 anode shows excellent electrochemical performance with a specific capacity of^1,400 mA·h·g^(−1)and a capacity retention of 98%after 100 cycles at the current of 0.2 A·g^(−1).