Enhancing thermodynamic stability of single-crystal Ni-rich cathode material via a synergistic dual-substitution strategy

Nickel(Ni)-rich cathode materials have become promising candidates for the next-generation electrical vehicles due to their high specific capacity.However,the poor thermodynamic stability(including cyclic performance and safety performance or thermal stability)will restrain their wide commercial application.Herein,a single-crystal Ni-rich Li Ni_(0.83)Co_(0.12)Mn_(0.05)O_(2) cathode material is synthesized and modified by a dual-substitution strategy in which the high-valence doping element improves the structural stability by forming strong metal–oxygen binding forces,while the low-valence doping element eliminates high Li^(+)/Ni^(2+)mixing.As a result,this synergistic dual substitution can effectively suppress H2-H3 phase transition and generation of microcracks,thereby ultimately improving the thermodynamic stability of Ni-rich cathode material.Notably,the dual-doped Ni-rich cathode delivers an extremely high capacity retention of 81%after 250 cycles(vs.Li/Li+)in coin-type half cells and 87%after 1000 cycles(vs.graphite/Li^(+))in pouch-type full cells at a high temperature of 55℃.More impressively,the dual-doped sample exhibits excellent thermal stability,which demonstrates a higher thermal runaway temperature and a lower calorific value.The synergetic effects of this dual-substitution strategy pave a new pathway for addressing the critical challenges of Ni-rich cathode at high temperatures,which will significantly advance the high-energy-density and high-safety cathodes to the subsequent commercialization.

Ether-/Ester-/Fluorine-Rich Binding Emulsion Formula for Lithium-Ion Batteries

Practical application of a Si anode in a high-energy-density battery cannot be achieved due to the huge volume expansion of these anodes.Researchers have focused on binders of the anode to restrict volume expansion in order to address this issue,as the hydrogen bonds and mechanical properties of binders can be used to enhance adhesion and accommodate the volume changes of a Si anode.Herein,we comprehensively consider binders’hydrogen bonds,mechanical properties,stability,and compatibility with the electrolyte solution,and design an ether-/ester-/fluorine-rich composite polymer,named P(TFEMAco-IBVE).The proposed binder formula possesses outstanding stability,adhesion,and mechanical strength;moreover,it can accommodate the dramatic volume changes of a Si electrode and exhibits excellent electrochemical performance,achieving a high areal capacity of about 5.4 mA·h·cm^(-2).This novel polymer design may be applied to other electrode materials in the next generation of lithium-ion batteries.

Selective Adsorption and Electrocatalysis of Polysulfides through Hexatomic Nickel Clusters Embedded in N-Doped Graphene toward High-Performance Li-S Batteries

The shuttle effect hinders the practical application of lithium-sulfur(Li-S)batteries due to the poor affinity between a substrate and Li polysulfides(LiPSs)and the sluggish transition of soluble LiPSs to insoluble Li2S or elemental S.Here,we report that Ni hexatomic clusters embedded in a nitrogen-doped three-dimensional(3D)graphene framework(Ni-N/G)possess stronger interaction with soluble polysulfides than that with insoluble polysulfides.The synthetic electrocatalyst deployed in the sulfur cathode plays a multifunctional role:(i)selectively adsorbing the polysulfides dissolved in the electrolyte,(ii)expediting the sluggish liquid-solid phase transformations at the active sites as electrocatalysts,and(iii)accelerating the kinetics of the electrochemical reaction of multielectron sulfur,thereby inhibiting the dissolution of LiPSs.The constructed S@Ni-N/G cathode delivers an areal capacity of 9.43mAhcm^(-2) at 0.1 C at S loading of 6.8 mg cm^(-2),and it exhibits a gravimetric capacity of 1104mAhg^(-1) with a capacity fading rate of 0.045%per cycle over 50 cycles at 0.2 C at S loading of 2.0 mg cm^(-2).This work opens a rational approach to achieve the selective adsorption and expediting of polysulfide transition for the performance enhancement of Li-S batteries.