Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries (LIBs).However,they suffer from voltage decay and low initial ...Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries (LIBs).However,they suffer from voltage decay and low initial Coulombic efficiency (ICE) due to severe structural degradation caused by irreversible O release.Herein,we introduce a three-in-one strategy of increasing Ni and Mn content,along with Li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of LLOs.The target material,Li_(1.2)Ni_(0.168)Mn_(0.558)Co_(0.074)O_(2)(L1),exhibits an improved ICE of 87.2%and specific capacity of 293.2 mA h g^(-1)and minimal voltage decay of less than 0.53 m V cycle-1over 300 cycles at 1C,compared to Li_(1.2)Ni_(0.13)Mn_(0.54)Co_(0.13)O_(2)(Ls)(274.4 mA h g^(-1)for initial capacity,73.8%for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C).Theoretical calculations reveal that the density of states (DOS) area near the Fermi energy level for L1 is larger than that of Ls,indicating higher anionic and cationic redox reactivity than Ls.Moreover,L1 exhibits increased O-vacancy formation energy due to higher Li/Ni disordering of 4.76%(quantified by X-ray diffraction Rietveld refinement) and enhanced TM–O covalency,making lattice O release more difficult and thus improving electrochemical stability.The increased Li/Ni disordering also leads to more Ni^(2+)presence in the Li layer,which acts as a pillar during Li+de-embedding,improving structural stability.This research not only presents a viable approach to designing low-Co LLOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance LIB cathodes.展开更多
Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg oc-cupancy,high transition metal-oxygen(TM-O)covalency,and lattice energy,which is essential to en-sure efficient and dura...Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg oc-cupancy,high transition metal-oxygen(TM-O)covalency,and lattice energy,which is essential to en-sure efficient and durable oxygen reduction reaction(ORR)process for perovskite lanthanide-transition metal oxides(LaTMO_(3)).However,due to the compositional complexity,clarifying the relevance among the high entropy components,eg occupancy,TM-O properties,and ORR performance still remains a chal-lenge.Herein,adopting the B site entropy-driven strategy,a series of LaTMO_(3)(TM=Cr,Mn,Fe,Co,Ni)with tunable eg occupancy and TM-O bond properties are synthesized,and the correlations between high entropy elements,eg occupancy,TM-O properties,and ORR performances are revealed quantitively based on the crystal field theory and the Phillips-Van Vechten-Levine(P-V-L)valence bond theory.High en-tropy La(Cr_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))O_(3)delivers a low overpotential of 493 mV(vs.503 mV for LaMnO_(3))and a minuscule decline by only 1.7%(vs.4.4%for LaMnO_(3))in half wave potential after 10,000 cycles,which can be associated with the tailored eg occupancy(1.06)and the significant enhancement in both TM-O covalency(4%)and lattice energy(691.75 kJ mol^(-1)).This work not only demonstrates the prospects of high entropy LaTMO_(3)in the ORR field but also provides a new perspective for the quantitative analysis of the structure-activity relationship for high entropy oxide ORR catalysts.展开更多
基金National Natural Science Foundation of China (No.52202046)Natural Science Foundation of Shaanxi Province (No.2021JQ-034)。
文摘Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries (LIBs).However,they suffer from voltage decay and low initial Coulombic efficiency (ICE) due to severe structural degradation caused by irreversible O release.Herein,we introduce a three-in-one strategy of increasing Ni and Mn content,along with Li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of LLOs.The target material,Li_(1.2)Ni_(0.168)Mn_(0.558)Co_(0.074)O_(2)(L1),exhibits an improved ICE of 87.2%and specific capacity of 293.2 mA h g^(-1)and minimal voltage decay of less than 0.53 m V cycle-1over 300 cycles at 1C,compared to Li_(1.2)Ni_(0.13)Mn_(0.54)Co_(0.13)O_(2)(Ls)(274.4 mA h g^(-1)for initial capacity,73.8%for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C).Theoretical calculations reveal that the density of states (DOS) area near the Fermi energy level for L1 is larger than that of Ls,indicating higher anionic and cationic redox reactivity than Ls.Moreover,L1 exhibits increased O-vacancy formation energy due to higher Li/Ni disordering of 4.76%(quantified by X-ray diffraction Rietveld refinement) and enhanced TM–O covalency,making lattice O release more difficult and thus improving electrochemical stability.The increased Li/Ni disordering also leads to more Ni^(2+)presence in the Li layer,which acts as a pillar during Li+de-embedding,improving structural stability.This research not only presents a viable approach to designing low-Co LLOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance LIB cathodes.
基金supported by the Key R&D Program of Shanxi Province(Nos.202102030201006 and 202202070301016)the National Natural Science Foundation of China(No.52072256)+3 种基金the Shanxi Science and Technology Major Project(No.20201101016)the Natural Science Foundation of Shanxi Province(Nos.20210302124105 and 20210302124308)the Centralized Guided Local Science and Technology Development Funds Project(No.YDZJSX2021B005)the Shanxi Provincial Science and Technology Innovation Base Construction Project(No.YDZJSX2022B003).
文摘Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg oc-cupancy,high transition metal-oxygen(TM-O)covalency,and lattice energy,which is essential to en-sure efficient and durable oxygen reduction reaction(ORR)process for perovskite lanthanide-transition metal oxides(LaTMO_(3)).However,due to the compositional complexity,clarifying the relevance among the high entropy components,eg occupancy,TM-O properties,and ORR performance still remains a chal-lenge.Herein,adopting the B site entropy-driven strategy,a series of LaTMO_(3)(TM=Cr,Mn,Fe,Co,Ni)with tunable eg occupancy and TM-O bond properties are synthesized,and the correlations between high entropy elements,eg occupancy,TM-O properties,and ORR performances are revealed quantitively based on the crystal field theory and the Phillips-Van Vechten-Levine(P-V-L)valence bond theory.High en-tropy La(Cr_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))O_(3)delivers a low overpotential of 493 mV(vs.503 mV for LaMnO_(3))and a minuscule decline by only 1.7%(vs.4.4%for LaMnO_(3))in half wave potential after 10,000 cycles,which can be associated with the tailored eg occupancy(1.06)and the significant enhancement in both TM-O covalency(4%)and lattice energy(691.75 kJ mol^(-1)).This work not only demonstrates the prospects of high entropy LaTMO_(3)in the ORR field but also provides a new perspective for the quantitative analysis of the structure-activity relationship for high entropy oxide ORR catalysts.
