Recent advances of composite electrolytes for solid-state Li batteries

All-solid-state lithium batteries(ASSLBs)are recognized as high energy density batteries system without safety issues within the next generation of batteries.The development of solid electrolytes is the crucial step of ASSLBs.The composite electrolyte has stable physical and electrochemical characteristics,and its comprehensive performance surpasses the individual solid electrolyte,bringing unique vitality to the solid electrolyte.However,their intrinsic weakness limits the development of composite electrolytes.In this review,we provide a comprehensive and in-depth understanding of the challenges and opportunities of composite electrolytes,with special focus on mechanisms of ion transport,nanostructure design towards high ionic conductivity,interfacial issues within electrolytes and electrodes.Furthermore,future development is prospected,which can shed light on researchers in this field and accelerate the industrial production of composite electrolytes.

Crack-free single-crystalline Co-free Ni-rich LiNi_(0.95)Mn_(0.05)O_(2) layered cathode

The rapid growth in global electric vehicles(EVs)sales has promoted the development of Co-free,Ni-rich layered cathodes for state-of-the-art high energy-density,inexpensive lithium-ion batteries(LIBs).However,progress in their commercial use has been seriously hampered by exasperating performance deterioration and safety concerns.Herein,a robust single-crystalline,Co-free,Ni-rich LiNi_(0.95)Mn_(0.05)O_(2)(SC-NM95)cathode is successfully designed using a molten salt-assisted method,and it exhibits better structural stability and cycling durability than those of polycrystalline LiNi_(0.95)Mn_(0.05)O_(2) (PC-NM95).Notably,the SC-NM95 cathode achieves a high discharge capacity of 218.2 mAh g^(-1),together with a high energy density of 837.3 Wh kg^(-1) at 0.1 C,mainly due to abundant Ni^(2+)/Ni^(3+) redox.It also presents an outstanding capacity retention(84.4%)after 200 cycles at 1 C,because its integrated single-crystalline structure effectively inhibits particle microcracking and surface phase transformation.In contrast,the PC-NM95 cathode suffers from rapid capacity fading owing to the nucleation and propagation of intergranular microcracking during cycling,facilitating aggravated parasitic reactions and rocksalt phase accumulation.This work provides a fundamental strategy for designing high-performance singlecrystalline,Co-free,Ni-rich cathode materials and also represents an important breakthrough in developing high-safe,low-cost,and high-energy LIBs.

Carbon dots for ultrastable solid-state batteries

Among the solid electrolytes for solid-state Li batteries,polymer electrolytes are actively explored on the basis of the good interfacial contact and easy making,while it is still constrained by slow ionic transport and low lithium ion transference number.Herein,functional carbon dots-based Li+conductor(CD-Li)is designed to improve the dynamics and selectivity of Li+transport in polyethylene oxide(PEO)electrolyte.High ionic conductivity(1.0×10^(−4) S/cm,25℃)and Li+transference number(0.60)were successfully achieved within the CD‐Li‐based PEO composite electrolyte,which could be attributed to the enhanced chain movement and the limited motion of anion.Moreover,the characteristics of big volume of individual anions of CD-Li can provide more free Li^(+).As well,benefiting from the existence of F atom in the CD-Li,in-situ constructed LiF-containing interfacial layer is in favor of maintaining the interface stability and facilitating the rapid transmission of Li ions.The composite electrolyte with CD-Li can address the ionic conductivity issues accompanied with strengthening the interfacial stability.The distinctive composite electrolyte realizes the stable cycle performance for Li/LiFePO_(4) and Li/LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)batteries.The exploration of multifunctional carbon dot fillers provides new ideas for the efficient development of composite electrolytes.