Na-ion batteries （NIBs） are considered one of the most attractive alternatives for Li-ion batteries （LIBs） because of the natural abundance of Na and the similarities between the NIB technology and the well-establ...Na-ion batteries （NIBs） are considered one of the most attractive alternatives for Li-ion batteries （LIBs） because of the natural abundance of Na and the similarities between the NIB technology and the well-established LIB technology. However, the discovery of high-performance electrode materials remains a key factor in the success of NIBs. Herein, we propose a new type of cathode material for NIBs based on a nanocomposite of an alkali metal fluoride （NaF） and a transition metal fluoride （FeF2）. Although neither of these components is electrochemically active with Na, the nanoscale mixture of the two can deliver a reversible capacity of -125 mAh/g in the voltage range of 1.2--4.8 V vs. Na/Na＋ via an Fe2＋/Fe3＋ redox couple. X-ray absorption spectroscopy reveals that the reversible Na storage is aided by the F-ions due to the decomposition of NaF, which are absorbed on the surface of FeF2, promoting the redox reaction of Fe and triggering the gradual transformation of the mother structure （FeF2） into a new （FeFB-like） host structure for the Na ions. This unique Na-ion storage phenomenon, which is reported for the first time, will introduce an avenue for designing novel cathode materials for NIBs.展开更多
First-principle calculation was used to investigate the magnetic properties, electronic structure and bonding mechanism of FeF2. By calculating the lattice parameters and magnetic moment as a function of effective int...First-principle calculation was used to investigate the magnetic properties, electronic structure and bonding mechanism of FeF2. By calculating the lattice parameters and magnetic moment as a function of effective interaction parameter （Ueff）, it is found that the optimum value of Uefr is equal to 4 eV, the magnetic moment is 3.752 μB and the value of c/a is 0.704, which are in good agreement with the experiment results. Simultaneously, on the basis of GGA＋U method, the electronic structure and bonding mechanism of FeF2 were investigated by the analysis of electron localization function, Bader charge and total charge density. The results show that the bonding behavior between Fe and F atoms is a combination of ionic and covalent bond.展开更多
文摘Na-ion batteries （NIBs） are considered one of the most attractive alternatives for Li-ion batteries （LIBs） because of the natural abundance of Na and the similarities between the NIB technology and the well-established LIB technology. However, the discovery of high-performance electrode materials remains a key factor in the success of NIBs. Herein, we propose a new type of cathode material for NIBs based on a nanocomposite of an alkali metal fluoride （NaF） and a transition metal fluoride （FeF2）. Although neither of these components is electrochemically active with Na, the nanoscale mixture of the two can deliver a reversible capacity of -125 mAh/g in the voltage range of 1.2--4.8 V vs. Na/Na＋ via an Fe2＋/Fe3＋ redox couple. X-ray absorption spectroscopy reveals that the reversible Na storage is aided by the F-ions due to the decomposition of NaF, which are absorbed on the surface of FeF2, promoting the redox reaction of Fe and triggering the gradual transformation of the mother structure （FeF2） into a new （FeFB-like） host structure for the Na ions. This unique Na-ion storage phenomenon, which is reported for the first time, will introduce an avenue for designing novel cathode materials for NIBs.
基金Foundation item: Project (20871101) supported by the National Natural Science Foundation of ChinaProject (09C945) supported by the Scientific Research Fund of Hunan Provincial Education Department,China
文摘First-principle calculation was used to investigate the magnetic properties, electronic structure and bonding mechanism of FeF2. By calculating the lattice parameters and magnetic moment as a function of effective interaction parameter （Ueff）, it is found that the optimum value of Uefr is equal to 4 eV, the magnetic moment is 3.752 μB and the value of c/a is 0.704, which are in good agreement with the experiment results. Simultaneously, on the basis of GGA＋U method, the electronic structure and bonding mechanism of FeF2 were investigated by the analysis of electron localization function, Bader charge and total charge density. The results show that the bonding behavior between Fe and F atoms is a combination of ionic and covalent bond.
