Electrochemical reconstruction: a new perspective on Sn metal-organic complex microbelts as robust anode for lithium storage

Tin-based materials with high theoretical capacity and suitable working voltage are ideal anode materials for lithium-ion batteries(LIBs). However, to overcome their shortcomings(volume expansion and inferior stability), the preparation processes are usually complicated and expensive. Herein, a tin-based metal-organic complex(tin 1,2-benzenedicarboxylic acid, Sn-BDC)with one-dimensional microbelt morphology is synthesized by a facile, rapid and low-cost co-precipitation method, and served as anode material for LIBs without any post-treatment. Sn-BDC exhibits a high reversible capacity with609/440 m Ah·g^(-1) at 50/2000 m A·g^(-1), and robust cycling stability of 856 m Ah·g^(-1) after 200 cycles at 200 m A·g^(-1),which are obviously superior to that of the Sn Ox/C counterparts. Moreover, an electrochemical reconstruction perspective on the lithium storage mechanism of Sn-BDC is proposed by systematic ex-situ characterizations. The reconstructed SnO_(2) replaces Sn-BDC and becomes the active material in the subsequent cycles. As the by-product of the lithiation reaction, the formed Li-based metal-organic complex(Li-BDC, wrapped around the reconstructed SnO_(2)) plays an important role in alleviating volume expansion and accelerating the charge transfer kinetics.This work is beneficial to design and construct the new electrode materials based on the electrochemical reconstruction for advanced LIBs.

SnO_(2)/metal organic complex composite derived from low-temperature activated metal organic complex for advanced lithium storage

Sn-based metal organic complexes with coordination bonds,multi-active sites,and high theoretical capacity have attracted much attention as promising anodes for lithium ion batteries.However,the low electrical conductivity and huge volume changes restricted their electrochemical stability and practical utilization.Herein,Snbased anode with superior electrochemical performance,including a high reversible capacity of 1050.1 mAh·g^(-1)at 2 A·g^(-1)and a stable capacity of 1105.5 mAh·g^(-1)after 500 cycles at 1 A·g^(-1),was fabricated via a low-temperature calcination strategy from Sn metal organic complexes.The low-temperature calcination process regulates Sn-O bond and prevents the agglomeration of SnO_(2),generating highly dispersed SnO_(2) decorated metal organic complexes and providing sufficient active sites for ion storage.Ex situ characterizations expound that the undecomposed Sn-based metal organic complexes could be transformed into SnO_(2) during lithiation and delithiation,which enhances the electrical conductivity and induces a strong pseudo-capacitive behavior,accelerating the electrochemical kinetics;the multiple solid electrolyte interface with inflexible LiF and flexible ROCO_(2)Li buffers the volume variation of the electrode,resulting in its high electrochemical stability.This work provides a simple strategy for preparing excellent Sn-based anodes from metal organic complexes and reveals the lithium storage mechanism of the prepared Snbased anode.

Oxygen-deficient ammonium vanadate/GO composites with suppressed vanadium dissolution for ultra-stable high-rate aqueous zinc-ion batteries

The structural engineering of hydrated ammonium vanadate as a cathode for aqueous Zn-ion batteries has attracted significant research interest because of its ability to suppress vanadium dissolution and accelerate the electrochemical dynamics.Herein,a feasible fabrication strategy for oxygen-deficient(NH_(4))_(2)V_(10)O_(25)·xH_(2)O/GO(NVOH@GO)composites was proposed,and the charge storage mechanism was discussed.The results of characterization analysis showed that the introduction of graphene oxide(GO)not only enlarged the layer spacing and improved electrical conductivity,providing spacious channels for Zn^(2+)(de)intercalation and accelerating the ion diffusion dynamics,but also induced more oxygen vacancies,inhibited the dissolution of vanadium,and reduced self-discharging,offering additional and stable active sites for ion storage.The optimized NVOH@GO electrode delivered extraordinarily stable capacities of 334 mAh·g^(-1)after 2000 cycles at 5 A·g^(-1)and 238 mAh·g^(-1)after 10,000cycles at 20 A·g^(-1).Furthermore,ex-situ X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and Raman results systematically revealed the electrochemical mechanism,including a phase transition reaction and subsequent Zn^(2+)/H_(2)O co-(de)intercalation process.This study provides an effective strategy for expanding the interlayer spacing,inducing defect engineering,and enhancing the structural stability of vanadium-based cathodes for Zn-ion batteries and other multivalent aqueous ion batteries.

Analysis of meso-inhomogeneous deformation on a metal material surface under low-cycle fatigue

A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element（RVE）of the nickel-based GH4169 superalloy.Considering the plastic deformation mechanism at the grain level and the Bauschinger effect,a crystal plasticity model reflecting the nonlinear kinematic hardening of crystal slipping system is applied.The microscopic inhomogeneous deformation during cyclic loading is calculated through numerical simulation of crystal plasticity.The deformation inhomogeneity on the free surface of the RVE under cyclic loading is described respectively by using the following parameters：standard deviation of the longitudinal strain in macro tensile direction,statistical average of first principal strains,and standard deviation of longitudinal displacement.The relationship between the fatigue cycle number and the evolution of inhomogeneous deformation of the material’s free surface is investigated.This research finds that：（1）The inhomogeneous deformation of the material free surface is significantly higher than that of the RVE inside;（2）the increases of the characterization parameters of inhomogeneous deformation on the free surface with cycles reflect the local maximum deformation of the RVE growing during cyclic loading;（3）these parameters can be used as criteria to assess and predict the low-cycle fatigue life rationally.