Understanding Sulfur Redox Mechanisms in Different Electrolytes for Room-Temperature Na-S Batteries

This work reports influence of two different electrolytes,carbonate ester and ether electrolytes,on the sulfur redox reactions in room-temperature Na-S batteries.Two sulfur cathodes with different S loading ratio and status are investigated.A sulfur-rich composite with most sulfur dispersed on the surface of a carbon host can realize a high loading ratio(72%S).In contrast,a confined sulfur sample can encapsulate S into the pores of the carbon host with a low loading ratio(44%S).In carbonate ester electrolyte,only the sulfur trapped in porous structures is active via‘solid-solid’behavior during cycling.The S cathode with high surface sulfur shows poor reversible capacity because of the severe side reactions between the surface polysulfides and the carbonate ester solvents.To improve the capacity of the sulfur-rich cathode,ether electrolyte with NaNO_(3) additive is explored to realize a‘solid-liquid’sulfur redox process and confine the shuttle effect of the dissolved polysulfides.As a result,the sulfur-rich cathode achieved high reversible capacity(483 mAh g^(−1)),corresponding to a specific energy of 362 Wh kg^(−1) after 200 cycles,shedding light on the use of ether electrolyte for high-loading sulfur cathode.

Single-atomic tungsten-doped Co_(3)O_(4) nanosheets for enhanced electrochemical kinetics in lithium–sulfur batteries

The practical application of lithium–sulfur batteries(LSBs)is severely hindered by the undesirable shuttling of lithium polysulfides(LiPSs)and sluggish redox kinetics of sulfur species.Herein,a series of ultrathin singleatomic tungsten-doped Co_(3)O_(4)(Wx-Co_(3)O_(4))nanosheets as catalytic additives in the sulfur cathode for LSBs are rationally designed and synthesized.Benefiting from the enhanced catalytic activity and optimized electronic structure by W doping,the Wx-Co_(3)O_(4) not only reduces the shuttling of LiPSs but also decreases the energy barrier of sulfur redox reactions of sulfur species,leading to accelerated electrode kinetic.As a result,LSB cathodes with the use of 5.0 wt%W0.02-Co_(3)O_(4) as the electrocatalyst show the high reversible capacities of 1217.0 and 558.6 mAh g^(-1) at 0.2 and 5.0 C,respectively,and maintain a high reversible capacity of 644.6 mAh g^(-1) at 1.0 C(1.0 C=1675 mA g^(-1))after 500 cycles.With a high sulfur loading of 5.5 mg cm^(-2) and electrolyte–electrode ratio of 8μL_(electrolyte) mg_(sulfur)^(-1),the 5.0 wt%W_(0.02)-Co_(3)O_(4)-based sulfur cathode also retains a high reversible areal capacity of 3.86 mAh cm^(-2) at 0.1 C after 50 cycles with an initial capacity retention of 84.7%.

Ultra-light and flexible pencil-trace anode for high performance potassium-ion and lithium-ion batteries

Engineering design of battery configurations and new battery system development are alternative approaches to achieve high performance batteries. A novel flexible and ultra-light graphite anode is fabricated by simple friction drawing on filter paper with a commercial 8 B pencil.Compared with the traditional anode using copper foil as current collector, this innovative current-collector-free design presents capacity improvement of over 200% by reducing the inert weight of the electrode. The as-prepared pencil-trace electrode exhibits excellent rate performance in potassium-ion batteries(KIBs), significantly better than in lithium-ion batteries(LIBs), with capacity retention of 66% for the KIB vs. 28% for the LIB from 0.1 to 0.5 A g^(-1). It also shows a high reversible capacity of ～230 mAh g^(-1) at 0.2 A g^(-1), 75% capacity retention over350 cycles at 0.4 A g^(-1)and the highest rate performance(based on the total electrode weight) among graphite electrodes for K+ storage reported so far.

Effect of Sn substitution for Co on microstructure and electrochemical performance of AB_5 type La_(0.7)Mg_(0.3)Al_(0.3)Mn_(0.4)Co_(0.5-x)Sn_xNi_(3.8)(x=0-0.5) alloys

The effects of substitution of Sn for Co on the microstructure, hydrogen storage and electrochemical discharge capacity of La0.7Mg0.3Al0.3Mn0.4Co0.5-xSnxNi3.8 （x=0, 0.1, 0.2, 0.3 and 0.5） alloys were investigated using X-ray diffraction （XRD）, pressure composition isotherm （PCT） and electrochemical discharge cycle. XRD, scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） tests showed that all of alloys are mainly composed of LaNi5 and MgNi2 phases, but when increasing the content of Sn in alloys, the LaNiSn phase appears and microstructure is refined. The PCT showed that increasing substitution of Sn for Co results in decrease of the maximum hydrogen storage capacity from 1.48% （x=0） to 0.85% （x=0.5）. The electrochemical tests indicated that the maximum discharge capacity decreases from 337.1 mA-h/g （x=0） to 239.8 mA.h/g （x=0.5）; however, the discharge capacity retention at the 100th cycle increases from 70.2% （x=0） to 78.0% （x=0.5）.

Design strategies of performance-enhanced Se cathodes for Li-Se batteries and beyond

Lithium-selenium(Li-Se)batteries are deemed as an emerging high energy density electrochemical energy storage system owing to their high specific capacity and volume capacity.Prior to their practicality,a series of critical challenges from the Se cathode side need to be overcome including low reactivity of bulk Se,shuttle effect of intermediates,sluggish redox kinetics of polyselenides,and volume change etc.In this review,recent progress on design strategies of functional Se cathodes are comprehensively summarized and discussed.Following the significance and key challenges,various efficient functionalized strategies for Se cathodes are presented,encompassing covalent bonding,nanostructure construction,heteroatom doping,component hybridization,and solid solution formation.Specially,the universality of these functional strategies are successfully extended into Na-Se batteries,K-Se batteries,and Mg-Se batteries.At last,a brief summary is made and some perspectives are offered with the goal of guiding future research advances and further exploration of these strategies.

SnSb@carbon nanocable anchored on graphene sheets for sodium ion batteries

The development of materials with unique nanostructures is an effective strategy for the improvement of sodium storage in sodium ion batteries to achieve stable cycling performance and good rate capability. In this work, SnSb- core/carbon-shell nanocables directly anchored on graphene sheets （GS） were synthesized by the hydrothermal technique and chemical vapor deposition. The simultaneous carbon coating and the encapsulation of SnSb alloy is effective for alleviating the volume-change problem in sodium ion batteries. After optimizing the electrolyte for SnSb in the sodium ion batteries, the optimized coaxial SnSb/carbon nanocable/GS （SnSb/CNT@GS） nanostructure demonstrated stable cycling capability and rate performance in 1 M NaClO4 with propylene carbonate （PC） ＋ 5% fluoroethylene carbonate （FEC）. The SnSb/CNT@GS electrode can retain a capacity of 360 mAh/g for up to 100 cycles, which is 71% of the theoretical capacity. This is higher than in the other three electrolytes tested （1 M NaClO4 in PC, 1 M NaC104 in PC/FEC （1：1 v/v） and 1 M NaPF6 ＋ PC）, and higher than that of the sample without the addition of graphene. The good electrochemical performance can be attributed to the efficient buffering provided by the outer carbon nanocable layer and the graphene inhibiting the agglomeration of SnSb particles, as well as its high conductivity.