Metal‐organic frameworks (MOFs) are of quite a significance in the field of inorganic‐organic hybrid crystals. Especially, MOFs have attracted increasing attention in recent years due to their large specific surface area, desirable electrical conductivity, controllable porosity, tunable geometric structure, and excellent thermal/chemical stability. Some recent studies have shown that carbon materials prepared by MOFs as precursors can retain the privileged structure of MOFs, such as large specific surface area and porous structure and, in contrast, realize in situ doping with heteroatoms (eg, N, S, P, and B). Moreover, by selecting appropriate MOF precursors, the composition and morphology of the carbon products can be easily adjusted. These remarkable structural advantages enable the great potential of MOF‐derived carbon as high‐performance energy materials, which to date have been applied in the fields of energy storage and conversion systems. In this review, we summarize the latest advances in MOF‐derived carbon materials for energy storage applications. We first introduce the compositions, structures, and synthesis methods of MOF‐derived carbon materials, and then discuss their applications and potentials in energy storage systems, including rechargeable lithium/sodium‐ion batteries, lithium‐sulfur batteries, supercapacitors, and so forth, in detail. Finally, we put forward our own perspectives on the future development of MOF‐derived carbon materials.

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The failure mechanism of LiFePO4 cells in over-discharge conditions has been systematically studied using commercial A123 18650 cells at a 1.0 C rate and different conditions – from 5% to 20% over-discharge (DOD = 105% to 120%). SEM/EDAX, high-energy synchrotron XRD (HESXRD), and cyclic voltammetry (CV) were used to characterize the morphology, structure, and electrode potentials of cell components both in situ and ex situ. The failure behaviors of A123 18650 cells experiencing different degrees of over-discharge were found to be similar, and the 20% over-discharge process was analyzed as the representative example. The Cu electrochemical potentials in the 1.2 M LiPF6 EC/EMC electrolyte were measured during the charge/over-discharge process using CV, proving that Cu oxidation and reduction in the cell during the charge/over-discharge cycle were theoretically possible to proceed. A possible failure mechanism is proposed: during the over-discharging process, Cu foil oxidized first to Cu+, then to Cu2+ cations; next, these Cu+ and Cu2+ cations diffused to the cathode side from the anode side; and finally, these Cu2+ cations reduced to Cu+ cations, and then reduced further, back to metallic Cu. During charge/over-discharge cycling, Cu dendrites continued growing from the cathode side, penetrating through the separator and forming a copper bridge between the anode and cathode. The copper bridge caused micro-shorting and eventually led to the failure of the cell. During the charge/over-discharge cycles, the continued cell temperature increase at the end of over-discharge is evidence of the micro-shorting.

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We have performed operando synchrotron high-energy X-ray diffraction (XRD) to obtain nonintrusive, real-time monitoring of the dynamic chemical and structural changes in commercial 18650 LiFePO4/C cells under realistic cycling conditions. The results indicate a nonequilibrium lithium insertion and extraction in the LiFePO4 cathode, with neither the LiFePO4 phase nor the FePO4 phase maintaining a static composition during lithium insertion/extraction. On the basis of our observations, we propose that the LiFePO4 cathode simultaneously experiences both a two-phase reaction mechanism and a dual-phase solid-solution reaction mechanism over the entire range of the flat voltage plateau, with this dual-phase solid-solution behavior being strongly dependent on charge/discharge rates. The proposed dual-phase solid-solution mechanism may explain the remarkable rate capability of LiFePO4 in commercial cells.

Electrochemical impedance spectroscopy (EIS) studies were carried out on commercial 18650 LiFePO 4 cells at different States of Charge (SOCs) to investigate failure in over-discharge conditions. The charge/discharge curves, capacity, charge acceptance, temperature, and impedance were characterized and analyzed. The EIS results show that the de-convoluted Ohmic resistance, R 0 , solid electrolyte interphase (SEI) resistance, R SEI , and Warburg Coefficient, σ, change with cycle number in some patterns, indicating the occurrence of corrosion of the current collector, SEI breakdown/decomposition and reformation, and the development of diffusion barriers of Li + in the electrode, respectively. These parameters, R 0 , R SEI , and σ are associated with failure and can be used as indicators of incoming failure. The EIS results from the three-electrode system verify that the EIS results from the twoelectrode system (practical 18650 cells) are reliable, which lays the foundation for the use of electrochemical impedance on practical applications of LIB cells. Overall, electrochemical impedance spectroscopy can be used as an effective and reliable tool to monitor the state of health, predict incoming failure of the cell, and issue a warning before failure without disturbing the operation of the cell.

The failure mechanism of LiFePO 4 cells during overcharge conditions has been systematically studied using commercial A123 18650 cells at a 1C rate and different conditions -from 5% to 20% overcharge (SOC = 105% to 120%). SEM/EDX, high-energy synchrotron XRD (HESXRD), and cyclic voltammetry (CV) were used to characterize the morphology, structure, and electrode potentials of cell components both in situ and ex situ. The failure behaviors for A123 18650 cells experiencing different degrees of overcharges were found to be similar, and the 10% overcharge process was analyzed as the representative example. The Fe redox potentials in the 1.2 M LiPF 6 EC/EMC electrolyte were measured during the overcharge/discharge process using CV, proving that Fe oxidation and reduction in the cell during the overcharge/discharge cycle is theoretically possible. A possible failure mechanism is proposed: during the overcharging process, metallic Fe oxidized first to Fe 2+ , then to Fe 3+ cations; next, these Fe 2+ and Fe 3+ cations diffused to the anode side from the cathode side; and finally, these Fe 3+ cations reduced first to Fe 2+ cations, and then reduced further, back to metallic Fe. During overcharge/discharge cycling, Fe dendrites continued growing from both the anode and the cathode sides simultaneously, penetrating through the separator and forming an iron bridge between the anode and cathode. The iron bridge caused micro-shorting and eventually led to the failure of the cell. During the overcharge/discharge cycles, the continued cell temperature increase at the end of overcharge is evidence of the micro-shorting.