Electrochemical reaction mechanism of porous Zn_(2)Ti_(3)O_(8)as a high-performance pseudocapacitive anode for Li-ion batteries

Zn_(2)Ti_(3)O_(8),as a new type of anode material for lithium-ion batteries,is attracting enormous attention because of its low cost and excellent safety.Though decent capacities have been reported,the electrochemical reaction mechanism of Zn_(2)Ti_(3)O_(8)has rarely been studied.In this work,a porous Zn_(2)Ti_(3)O_(8)anode with considerably high capacity(421 mAh/g at 100 mA/g and 209 mAh/g at 5000 mA/g after 1500 cycles)was reported,which is even higher than ever reported titanium-based anodes materials including Li_(4)Ti_(5)O_(12),TiO_(2)and Li_(2)ZnTi_(3)O_(8).Here,for the first time,the accurate theoretical capacity of Zn_(2)Ti_(3)O_(8)was confirmed to be 266.4 mAh/g.It was also found that both intercalation reaction and pseudocapacitance contribute to the actual capacity of Zn_(2)Ti_(3)O_(8),making it possibly higher than the theoretical value.Most importantly,the porous structure of Zn_(2)Ti_(3)O_(8)not only promotes the intercalation reaction,but also induces high pseudocapacitance capacity(225.4 mAh/g),which boosts the reversible capacity.Therefore,it is the outstanding pseudocapacitance capacity of porous Zn_(2)Ti_(3)O_(8)that accounts for high actual capacity exceeding the theoretical one.This work elucidates the superiorities of porous structure and provides an example in designing high-performance electrodes for lithium-ion batteries.

Graphite Anode for Potassium Ion Batteries: Current Status and Perspective

With the increased demand from the storage of renewable energy sources,some safe and inexpensive energy storage technologies instead of Li-ion batteries become urgently needed.Therefore,K-ion batteries(KIBs)have attracted much attention and evolved significant development because of the low price,safety,and similar property compared with Li-ion batteries.Due to the high reversibility,stability,and low potential plateau,graphite becomes a current research focus and is regarded as one of the most promising KIB’s anode materials.In this review,we mainly discuss the electrochemical reaction mechanism of graphite during potassiation-depotassiation process and analyze the effects of electrode/electrolyte interface on graphite for Kion storage.Besides,we summarize several kinds of methods to improve the performance of graphite for KIBs,including the design of graphite structure,selection of appropriate binder,solvent chemistry,and salt chemistry.Meanwhile,a concept of“relative energy density”is raised,which can be more accurate to evaluate the genuine electrochemical performance of graphite anode involving the specific capacity and potential.In addition,we also summarize the considerable challenges to current graphite anode in KIBs and we believe our work will offer alterative solutions to further explore high-performance graphite anode of K-ion storage.

Transition metal carbonate anodes for Li-ion battery: fundamentals,synthesis and modification

Even though transition metal carbonates(TMCs, TM = Fe, Mn, Co, Ni etc.), show high theoretical capacities, rich reserves and environmental friendliness as anodes for lithium-ion batteries(LIBs), they suffer from sluggish electronic/ionic conductivities and huge volume variation, which severely deteriorate the rate capacities and cycling performances. Understanding the intrinsic reaction mechanism and further developing ideal TMC-based anode with high specific capacity, excellent rate capabilities, and longterm cycling stability are critical for the practical application of TMCs. In this review, we firstly focus on the fundamental electrochemical energy-storage mechanisms of TMCs, in terms of conversionreaction process, pseudocapacitance-type charge storage, valence change for charge storage and catalytic conversion mechanisms. Based on the reaction mechanisms, various modification strategies to improve the electrochemical performance of TMCs are summarized, covering:(i) micro-nano structural engineering, in which the influence factors on the morphology are discussed, and multiple architectures are listed;(ii) elemental doping, in which the intrinsic mechanisms of metal/nonmetal elements doping on the electrochemical performance are deeply explored;(iii) multifunctional compositing strategies, in which the specific affections on structure, electronic conductivity and chemo-mechanical stability are summarized.Finally, the key challenges and opportunities to develop high-performance TMCs are discussed and some solutions are also proposed. This timely review sheds light on the path towards achieving cost-effective and safe LIBs with high energy density and long cycling life using TMCs-based anode materials.

V-substituted pyrochlore-type polyantimonic acid for highly enhanced lithium-ion storage

Pyrochlore-structured polyantimonic acid(PAA)is a potential high-capacity electrode material,but its innately poor electroconductivity(~10^(-10)S/cm)seriously impairs its electrochemical reversibility for lithium-ion storage.Herein,we report design and synthesis of a novel V-substituted PAA(PAA-V),where V^(5+)are introduced to partially replace Sb^(5+).Owing to identical valence and close ionic radius relative to Sb^(5+),the V^(5+)cation can constitute the covalent VO_6octahedra framework without changing the pyrochlore crystal structure of PAA.As a result,the V^(5+)-substitution is capable to modulate the electronic structure of PAA with significantly improved electrical conductivity(~10^(-6)S/cm for PAA-V)and meanwhile decreases the size of crystals with reduced diffusion length for Li^(+)-ions.With varying the ratio of V^(5+)-substitution,the PAA-V with optimized substitution molar ratio(18%)exhibits the best lithium-ion storage performance,delivering a long cycling life with high reversible capacity(731 m Ah/g after 1200cycles at 1 A/g)and outstanding rate capability(279 mAh/g at 15 A/g).More importantly,by pairing the PAA-V as anode and commercial LiFePO_(4)as cathode,the full cell with a limited negative/positive capacity ratio of 1.2 exhibits decent cycling stability at 1 C after 150 cycles with 85.5%capacity retention.