Biphase-to-monophase structure evolution of Na_(0.766+x)Li_(x)Ni_(0.33-x)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) toward ultradurable Na-ion batteries

Layered composite oxide materials with O3/P2 biphasic crystallographic structure typically demonstrate a combination of high capacities of the O3 phase and high operation voltages of the P2 phase.However,their practical applications are seriously obstructed by difficulties in thermodynamic phase regulation,complicated electrochemical phase transition,and unsatisfactory cycling life.Herein,we propose an efficient structural evolution strategy from biphase to monophase of Na_(0.766+x)Li_(x)Ni_(0.33-x)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) through Li+substitution.The role of Li+substitution not only simplifies the unfavorable phase transition by altering the local coordination of transition metal(TM)cations but also stabilizes the cathode–electrolyte interphase to prevent the degradation of TM cations during battery cycling.As a result,the thermodynamically robust O_(3)-Na_(0.826)Li_(0.06)Ni_(0.27)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) cathode delivers a high capacity of 139.4 mAh g^(-1) at 0.1 C and shows prolonged cycling life at high rates,with capacity retention of 81.6%at 5 C over 500 cycles.This work establishes a solid relationship between the thermodynamic structure evolution and electrochemistry of layered cathode materials,contributing to the development of long-life sodium-ion batteries.

Tuning dual-atom mediator toward high-rate bidirectional polysulfide conversion in Li-S batteries

An emerging practice in the realm of Li-S batteries lies in the employment of single-atom catalysts(SACs)as effective mediators to promote polysulfide conversion,but monometallic SACs affording isolated geometric dispersion and sole electronic configuration limit the catalytic benefits and curtail the cell performance.Here,we propose a class of dual-atom catalytic moieties comprising hetero-or homo-atomic pairs anchored on N-doped graphene(NG)to unlock the liquid–solid redox puzzle of sulfur,readily realizing Li-S full cell under high-rate-charging conditions.As for Fe-Ni-NG,in-depth experimental and theoretical analysis reveal that the hetero-atomic orbital coupling leads to altered energy levels,unique electronic structures,and varied Fe oxidation states in comparison with homo-atomic structures(FeFe-NG or Ni-Ni-NG).This would weaken the bonding energy of polysulfide intermediates and thus enable facile electrochemical kinetics to gain rapid liquid-solid Li_(2)S_(4)?Li_(2)S conversion.Encouragingly,a Li-S battery based on the S@Fe-Ni-NG cathode demonstrates unprecedented fast-charging capability,documenting impressive rate performance(542.7 mA h g^(-1)at 10.0 C)and favorable cyclic stability(a capacity decay of 0.016%per cycle over 3000 cycles at 10.0 C).This finding offers insights to the rational design and application of dual-atom mediators for Li-S batteries.

Boosting polysulfide redox conversion of Li-S batteries by one-step-synthesized Co-Mo bimetallic nitride

Lithium-sulfur(Li-S)batteries are considered as one of the most promising next generation energy storage systems due to the high theoretical specific capacity,low cost,and environmental benignity.However,the notorious shuttle effect of polysulfides hinders the practical application of Li-S batteries.Herein,we have rationally designed and synthesized sea urchin-like Co-Mo bimetallic nitride(Co_(3) MO_(3) N)in the absence of additional nitrogen sources with only one step,which was applied as the sulfur host materials for Li-S batteries.The results indicate that Co_(3) Mo_(3) N can efficiently anchor and catalyze the conversion of polysulfides,thus accelerating the electrochemical reaction kinetics and enabling prominent electrochemical properties.As a consequence,the S@Co_(3) Mo_(3) N cathode exhibits a high rate performance of 705 mAh g^(-1) at 3 C rate and an excellent cycling stability with a low capacity fading rate of 0.08%per cycle at 1 C over 600 cycles.Even at a high sulfur loading of 5.4 cmg cm^(-2),it delivers a high initial areal capacity of 4.50 mAh cm^(-2) which is still retained at 3.64 mAh cm^(-2) after 120 cycles.Furthermore,the catalytic mechanism and structural stability of Co_(3) Mo_(3) N during cycling were elucidated by a combination of X-ray photoelectron spectroscopy and X-ray absorption fine structure.This work highlights the strategy of structure-catalysis engineering of bimetallic nitride,which is expected to have a wide application in Li-S batteries.

Bidirectionally catalytic polysulfide conversion by high-conductive metal carbides for lithium-sulfur batteries

Utilizing catalysts to accelerate the redox kinetics of lithium polysulfides (LiPSs) is a promising strategy to alleviate the shuttle effect of lithium–sulfur (Li–S) batteries.Nevertheless,most of the reported catalysts are only effective for LiPSs reduction,resulting in the devitalization of catalysts over extended cycles as a consequence of the continuous accumulation of Li_(2)S passivation layer.The situation gets even worse when employing mono-directional catalyst with poor electron conductivity because the charge transfer for the decomposition of solid Li_(2)S is severely hampered.Herein,a high-conductive and dualdirectional catalyst Co_(3)C decorated on porous nitrogen-doped graphene-like structure and carbon nanotube (Co_(3)C@PNGr-CNT) is fabricated as sulfur host,which not only promotes the precipitation of Li_(2)S from Li PSs during discharge but also facilitates the decomposition of Li;S during subsequent charge,as evidenced by the reduced activation energies for both reduction and oxidation processes.Furthermore,the long-term catalytic stability of Co_(3)C is corroborated by the reversible evolution of Co–C bond length over extended cycles as observed from X-ray absorption fine structure results.As a consequence,the fabricated Co_(3)C@PNGr-CNT/S cathode delivers a low capacity decay of 0.043%per cycle over 1000 cycles at 2C.Even at high sulfur loading (15.6 mg cm^(-2)) and low electrolyte/sulfur (E/S) ratio (~8μL mg^(-1))conditions,the battery still delivers an outstanding areal capacity of 11.05 m Ah cm^(-2) after 40 cycles.This work provides a rational strategy for designing high-efficient bidirectional catalyst with single component for high-performance Li-S batteries.

Modulating eg orbitals through ligand engineering to boost the electrocatalytic activity of NiSe for advanced lithium-sulfur batteries

Accelerating the sluggish redox kinetics of lithium polysulfides(LiPSs)by electrocatalysis is essential to achieve high performance lithium-sulfur(Li-S)batteries.However,the issue of insufficient catalytic activity remains to be addressed.Herein,a strategy of modulating e_(g) orbitals through ligand engineering has been proposed to boost the catalytic activity of NiSe for rapid LiPSs redox conversion.The X-ray spectroscopic measurements and theoretical calculations reveal that partial substitution of Se with N disrupts the octahedral coordination of Ni atoms in NiSe,leading to the reduced degeneracy and upward shift of e_(g) orbitals of Ni 3 d states.As a consequence,the bonding strength of N-substituted NiSe(N-NiSe)with LiPSs is enhanced,which facilitates the interfacial charge transfer kinetics and accelerates the LiPSs redox kinetics.Therefore,the Li-S batteries assembled with N-NiSe present a high capacity of 682.6 mAh g^(-1) at a high rate of 5 C and a high areal capacity of 6.5 mAh cm^(-2)at a high sulfur loading of 6 mg cm^(-2).This work provides a promising strategy to develop efficient transition-metal based electrocatalysts for Li-S batteries through e_(g) orbital modulation.

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

Lithium–sulfur(Li–S)batteries are one of the most promising alternatives to lithium–ion batteries because of the advantageous high energy density and low cost.However,the practical applications of Li–S batteries are hampered by a severe shuttle effect and sluggish polysulfide redox conversion.Herein,highly dispersed cobalt nanoparticles(∼0.8 wt%)embedded into nitrogen-doped hierarchical porous carbon(Co@N-HPC)are designed as an effective electrocatalyst for Li–S batteries,which exhibit a synergistic effect of anchoring and dual-directional catalytic conversion of polysulfides.