Abstract:Iron fluoride, an intercalation-conversion cathode for lithium ion batteries, promises a high theoretical energy density of 1922 Wh kg–1. However, poor electrochemical reversibility due to repeated breaking/reformation of metal fluoride bonds poses a grand challenge for its practical application. Here we report that both a high reversibility over 1000 cycles and a high capacity of 420 mAh g−1 can be realized by concerted doping of cobalt and oxygen into iron fluoride. In the doped nanorods, an energy density o… Show more
“…As shown in Figure 4, the seven pyrenetetrone derivatives are predicted to have the specific charge capacities of 201–496 mAh/g and the specific energy densities of 424–913 mWh/g. Strikingly, 4N-pyrenetetrone, which can store up to five Li atoms, exhibits the remarkably high performance (496 mAh/g and 913 mWh/g) with five different plateaus in the profiles, outperforming conventional inorganic cathode materials (LiCoO 2 : 274 mAh/g; LiFePO 4 : 162 mAh/g and 90–110 mWh/g; Li[Ni x Co y Mn 1−x−y ]O 2 ( x > 0.9): 220 mAh/g; Fe 0.9 Co 0.1 OF nanorods: 420 mAh/g and ∼1000 mWh/g) (Qian et al., 2018, Yamada et al., 2001, Kim et al., 2018, Fan et al., 2018) and other insoluble high-performance organic cathode materials (quinone-based polymers: ∼396 mAh/g; poly(benzoquinonyl sulfide: 734 mWh/g) (Wu et al., 2017, Song et al., 2015a, Song et al., 2015b). Figure 4Performance ParametersProfiles of (A) the charge capacities and (B) the energy densities as a function of the calculated redox potential for seven pyrenetetrone derivatives.…”
SummaryTo overcome limited information on organic cathode materials for lithium-ion batteries, we studied the electrochemical redox properties of pyrenetetrone and its nitrogen-doped derivatives. Three primary conclusions are highlighted from this study. First, the redox potential increases as the number of electron-withdrawing nitrogen dopants increases. Second, the redox potentials of pyrenetetrone derivatives continuously decrease with the number of bound Li atoms during the discharging process owing to the decrease in the reductive ability until the compounds become cathodically deactivated exhibiting negative redox potentials. Notably, pyrenetetrone with four nitrogen dopants loses its cathodic activity after the binding of five Li atoms, indicating remarkably high performance (496 mAh/g and 913 mWh/g). Last, the redox potential is strongly correlated not only with electronic properties but also with solvation energy. This highlights that pyrenetetrone derivatives would follow two-stage transition behaviors during the discharging process, implying a crucial contribution of solvation energy to their cathodic deactivation.
“…As shown in Figure 4, the seven pyrenetetrone derivatives are predicted to have the specific charge capacities of 201–496 mAh/g and the specific energy densities of 424–913 mWh/g. Strikingly, 4N-pyrenetetrone, which can store up to five Li atoms, exhibits the remarkably high performance (496 mAh/g and 913 mWh/g) with five different plateaus in the profiles, outperforming conventional inorganic cathode materials (LiCoO 2 : 274 mAh/g; LiFePO 4 : 162 mAh/g and 90–110 mWh/g; Li[Ni x Co y Mn 1−x−y ]O 2 ( x > 0.9): 220 mAh/g; Fe 0.9 Co 0.1 OF nanorods: 420 mAh/g and ∼1000 mWh/g) (Qian et al., 2018, Yamada et al., 2001, Kim et al., 2018, Fan et al., 2018) and other insoluble high-performance organic cathode materials (quinone-based polymers: ∼396 mAh/g; poly(benzoquinonyl sulfide: 734 mWh/g) (Wu et al., 2017, Song et al., 2015a, Song et al., 2015b). Figure 4Performance ParametersProfiles of (A) the charge capacities and (B) the energy densities as a function of the calculated redox potential for seven pyrenetetrone derivatives.…”
SummaryTo overcome limited information on organic cathode materials for lithium-ion batteries, we studied the electrochemical redox properties of pyrenetetrone and its nitrogen-doped derivatives. Three primary conclusions are highlighted from this study. First, the redox potential increases as the number of electron-withdrawing nitrogen dopants increases. Second, the redox potentials of pyrenetetrone derivatives continuously decrease with the number of bound Li atoms during the discharging process owing to the decrease in the reductive ability until the compounds become cathodically deactivated exhibiting negative redox potentials. Notably, pyrenetetrone with four nitrogen dopants loses its cathodic activity after the binding of five Li atoms, indicating remarkably high performance (496 mAh/g and 913 mWh/g). Last, the redox potential is strongly correlated not only with electronic properties but also with solvation energy. This highlights that pyrenetetrone derivatives would follow two-stage transition behaviors during the discharging process, implying a crucial contribution of solvation energy to their cathodic deactivation.
“…Substitution of another element into binary oxides could improve the electrochemical properties via in situ formation of metallic support, which can accommodate volumetric changes and provide facile pathways for electrons 55 . Furthermore, a recent strategy of co-substitution/doping of both cation and anion sheds light on changing the reaction nature: improving the integrity and the electronic conductivity of materials, which may resolve the problematic issues intrinsically 56 .…”
Batteries with conversion-type electrodes exhibit higher energy storage density but suffer much severer capacity fading than those with the intercalation-type electrodes. The capacity fading has been considered as the result of contact failure between the active material and the current collector, or the breakdown of solid electrolyte interphase layer. Here, using a combination of synchrotron X-ray absorption spectroscopy and in situ transmission electron microscopy, we investigate the capacity fading issue of conversion-type materials by studying phase evolution of iron oxide composited structure during later-stage cycles, which is found completely different from its initial lithiation. The accumulative internal passivation phase and the surface layer over cycling enforce a rate−limiting diffusion barrier for the electron transport, which is responsible for the capacity degradation and poor rate capability. This work directly links the performance with the microscopic phase evolution in cycled electrode materials and provides insights into designing conversion-type electrode materials for applications.
“…At present, metal fluoride materials such as FeF 3 , FeF 2 , CuF 2 , and CoF 2 are facing severe limitations in terms of low reversibility, large voltage hysteresis, rather poor rate capability, detrimental active material dissolution, and poor cycle life . To mitigate these issues, ball milling, particle designs, doping chemistry, and electrolyte modifications have been reported with the target of improving transport and reaction kinetics, stabilizing reaction interface, and suppressing active material dissolution and the related shuttle effects . Typically, the chemical precipitation, sol–gel, hydrothermal, thermal decomposition, solid–solid reaction, and solid–gas reaction methods based on different fluorine sources (e.g., HF, F 2 , NH 4 F, NH 4 HF 2 , CF x , metal hexafluorosilicate, NF 3 , F‐containing ionic liquids, etc.)…”
mentioning
confidence: 99%
“…However, this only provided a cycling performance over 300 cycles at ≈0.42C rate undergoing a one‐electron reaction . In addition to modifications of Li salts, ultrahigh and unusual F‐containing solvents were used to improve the capacity and cycle stability of Fe 0.9 Co 0.1 OF cathode . However, the highly concentrated electrolyte and the unusual expensible solvents were not feasible for a practical application.…”
Lithium-ion (Li-ion) batteries as one of the most popular energy storage systems have been widely used in laptops, mobile phones, cameras, electric tools, and cars. However, the commercial Li-ion batteries employing Ni-and Co-based intercalation-type cathodes with limited capacities and energy densities cannot meet the rapidly rising market demands in Metal fluoride-lithium batteries with potentially high energy densities, even higher than lithium-sulfur batteries, are viewed as very promising candidates for next-generation lightweight and low-cost rechargeable batteries. However, so far, metal fluoride cathodes have suffered from poor electronic conductivity, sluggish reaction kinetics and side reactions causing high voltage hysteresis, poor rate capability, and rapid capacity degradation upon cycling. Herein, it is reported that an FeF 3 @C composite having a 3D honeycomb architecture synthesized by a simple method may overcome these issues. The FeF 3 nanoparticles (10-50 nm) are uniformly embedded in the 3D honeycomb carbon framework where the honeycomb walls and hexagonal-like channels provide sufficient pathways for the fast electron and Li-ion diffusion, respectively. As a result, the as-produced 3D honeycomb FeF 3 @C composite cathodes even with high areal FeF 3 loadings of 2.2 and 5.3 mg cm −2 offer unprecedented rate capability up to 100 C and remarkable cycle stability within 1000 cycles, displaying capacity retentions of 95%-100% within 200 cycles at various C rates, and ≈85% at 2C within 1000 cycles. The reported results demonstrate that the 3D honeycomb architecture is a powerful composite design for conversion-type metal fluorides to achieve excellent electrochemical performance in metal fluoride-lithium batteries.
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