Lithiophilic Anti-perovskite Nitrides For Structured Li Metal Anodes

Lithium metal has long been regarded as the ultimate anode candidate for high-energy-density batteries due to its ultrahigh theoretical specific capacity(3860 m Ah g^-1),the lowest negative electrochemical potential（-3.04 V vs.the standard hydrogen electrode）,and the smallest metal density(0.65 g cm^-3).However,the Li metal anode suffers from the“Dead Li”and infinite volume expansion,resulting in a rapid capacity decay and even an internal short circuit.To solve these problems,this dissertation focuses on investigating the Li nucleation behavior at the initial stage,combined with the kinetics of lithium ion and thermodynamic characteristics during the Li nucleating process.By virtue of the controllable tip-effect to realize the directional migration of lithium ions and uniform Li nucleation.Anti-perovskite nitride with stable and reversible lithiophilicity contributes to realizing the safe,efficient,and durable operation of Li metal batteries.The main contents and results of this dissertation are presented as follow:（1）By virtue of the controllable tip-effect can realize the directional migration of lithium ions and uniform Li nucleation on the electrodes.This innovative concept was validated by a typical model with Ag nanoparticles and graphene aerogel（Ag/GA）which can mitigate the inhomogeneous current distribution caused by the uncontrollable wrinkles/edges of GA,and densify the lithium deposition.We also identify the intrinsic influencing factors（size and distribution）of nano-tips for Li plating and illustrate the detailed process of Li nucleation/growth on Ag/GA anodes.Electrochemical tests show that Ag/GA anodes in the symmetric cell exhibit lower nucleation overpotential,better rate capability and longer cycle life than the cells with the intact graphene aerogel.More importantly,the excellent electrochemical performances of Ag/GA anodes are also verified in a Li Fe PO₄ coupled full cell with minimal degradation of capacity（17.1%）in 500 cycles under the charge/discharge current of 1C.（2）A low coast,highly conductive,and chemically stable lithiophilic material,anti-perovskite nitride ZnNNi₃ was synthesized by hydrothermal and thermal annealing processes（NH₃ atmosphere）and applied for constructing structural Li metal host.ZnNNi₃ exhibits an electronic conductivity of 24.8 S cm^-1 at 25 MP,much higher than that of Ni₃N(15.6 S cm^-1)and Ni O(2.1 S cm^-1).More importantly,the cyclic voltammetry（CV）and Li deposition behavior show no irreversible conversion reactions on the ZnNNi₃ modified electrode,suggesting its excellent chemical stability.In the coulombic efficiency（CE）test,the ZnNNi₃@Cu-Li half-cell maintains at 99.2%（average 99.17%）even after 500 cycles at 1.0 m A cm^-2,indicating high reversibility of Li.Furthermore,electrochemical properties including cycling performance and rate performance of ZnNNi₃/CC-based Li anodes are also analyzed through symmetric cells and full cells.In Li symmetric cell,the ZnNNi₃/CC-Li electrodes present a stable Li plating/strapping process over 2000 h at 1.0 m A cm^-2.And in Li Fe PO₄（LFP）coupled full cell,the capacity maintains at 72%of the initial stage after 1500 cycles,realizing an ultra-long cycle life.（3）Anti-perovskite nitride CuNNi₃with excellent lithiophility and chemical stability was synthesized and applied for structural Li metal anode.Systematically compared the physicochemical properties of CuNNi₃,InNNi₃,and ZnNNi₃.And according to the DFT calculations,CuNNi₃ possesses the highest average binding energy of 5.784 e V/atom and the strongest binding energy with Li atoms（-0.467 e V）,which not only ensures the favorable lithiophilic properties but also prevent oxygen atoms and lithium atoms from damaging the material structure.The cyclic voltammetry（CV）verified that no irreversible conversion reactions occurred on the CuNNi₃ modified electrode,indicating excellent chemical stability.In addition,CuNNi₃ nanoparticles with high distribution density and high uniformity can be realized on the carbon cloth electrode by the freeze-drying and nitriding method.In the coulombic efficiency（CE）test,the CuNNi₃@Cu-Li half-cell maintains above 99.8%even after400 cycles.And ZnNNi₃@CC-Li symmetric cell presents a stable Li plating/stripping behavior of 2400 h at 1.0 m A cm^-2.Furthermore,the ZnNNi₃@CC-based anode-free full cell can achieve a capacity retention of 91.3%after 60 cycles.（4）To meet the practical application,three kinds of anti-perovskite nitrides modified ultrathin structured anodes have been investigated.Graphene nanosheet based ultrathin structured host with large pore structures can provide sufficient deposition space for lithium deposition and ensure the good permeability of the electrolyte.As a result,Li metal can be uniformly deposited inside these electrodes after being lithophilization,and the Li composite anodes present good electrochemical performance.While,some ultrathin hosts such as carbon nanotube-based and MOFs-derived electrodes usually present small pore structures.The small pores cannot ensure the rapid infiltration of electrolytes inside the electrode,which limits the migration of Li ions,and Li metal cannot be uniformly deposited in the electrode.