The present work provides a novel one-step synthesis for nitrogen-doped activated carbon. The excellent performance of the N-doped AC allows its further application in a hybrid-type supercapacitor, which utilizes a combination of the capacitor electrode and a Li-ion battery anode.

Among the various energy-storage systems, lithium-ion capacitors (LICs) are receiving intensive attention due to their high energy density, high power density, long lifetime, and good stability. As a hybrid of lithium-ion batteries and supercapacitors, LICs are composed of a battery-type electrode and a capacitor-type electrode and can potentially combine the advantages of the high energy density of batteries and the large power density of capacitors. Here, the working principle of LICs is discussed, and the recent advances in LIC electrode materials, particularly activated carbon and lithium titanate, as well as in electrolyte development are reviewed. The charge-storage mechanisms for intercalative pseudocapacitive behavior, battery behavior, and conventional pseudocapacitive behavior are classified and compared. Finally, the prospects and challenges associated with LICs are discussed. The overall aim is to provide deep insights into the LIC field for continuing research and development of second-generation energy-storage technologies.

Silicon has been identified as a highly promising anode for next-generation lithium-ion batteries (LIBs). The key challenge for Si anodes is large volume change during the lithiation/delithiation cycle that results in chemomechanical degradation and subsequent rapid capacity fading. Here we report a novel fabrication method for hierarchically porous Si nanospheres (hp-SiNSs), which consist of a porous shell and a hollow core. On charge/discharge cycling, the hp-SiNSs accommodate the volume change through reversible inward Li breathing with negligible particle-level outward expansion. Our mechanics analysis revealed that such inward expansion is enabled by the much stiffer lithiated layer than the unlithiated porous layer. LIBs assembled with the hp-SiNSs exhibit high capacity, high power and long cycle life, which is superior to the current commercial Si-based anode materials. The low-cost synthesis approach provides a new avenue for the rational design of hierarchically porous structures with unique materials properties.

High‐performance activated carbons derived from the most common egg white are synthesized via a simple biomass transfer process. Hybrid‐type lithium‐ion supercapacitors (LICs) are fabricated utilizing the eAC as the cathode materials and Si/C nanocomposites as the anode material. The LIC exhibits high energy density and power density with an excellent cycling life.

Next‐generation Li‐ion batteries (LIBs) with higher energy density adopt some novel anode materials, which generally have the potential to exhibit higher capacity, superior rate performance as well as better cycling durability than conventional graphite anode, while on the other hand always suffer from larger active lithium loss (ALL) in the first several cycles. During the last two decades, various pre‐lithiation strategies are developed to mitigate the initial ALL by presetting the extra Li sources to effectively improve the first Coulombic efficiency and thus achieve higher energy density as well as better cyclability. In this progress report, the origin of the huge initial ALL of the anode and its effect on the performance of full cells are first illustrated in theory. Then, various pre‐lithiation strategies to resolve these issues are summarized, classified, and compared in detail. Moreover, the research progress of pre‐lithiation strategies for the representative electrochemical systems are carefully reviewed. Finally, the current challenges and future perspectives are particularly analyzed and outlooked. This progress report aims to bring up new insights to reassess the significance of pre‐lithiation strategies and offer a guideline for the research directions tailored for different applications based on the proposed pre‐lithiation strategies summaries and comparisons.

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high energy and power density, long cycle life, low cost, and environmental benignity. [3] Due to the high capacity of the currently used graphite anode −372 mAh g-1 , [1b,4] commercial cathodes have become the bottleneck for improving the energy density. [5] In addition, cathode materials take up about 40% of the total material cost of typical LIB cells. It is therefore crucial to develop cathode materials with high energy density and low cost, while maintaining superior safety features. [6] Driven by the wide deployment of electric vehicles in recent years, the demand for safer cathode materials with higher capacity and lower cost has become imperative. [2b] The specific capacity depends on the inherent physical properties of the cathode materials. Commercial materials such as LiCoO 2 , Li(Ni x Mn y Co z)O 2 , Li(Ni x Co y Al z)O 2 , LiMn 2 O 4 and LiFePO 4 all possess discharge capacities below 200 mAh g-1. [7] Ni-rich NCM, NCA, and Li-rich oxides are all prospective cathodes for high-energy LIBs as they can exhibit high specific discharge capacities above 200 mAh g-1. [6c] As compared with Ni-rich NCM and NCA, Li-rich Mn-based layered oxide (LMLO) cathode materials are cheaper and have higher specific capacity. They can deliver an initial specific discharge capacity that approaches 300 mAh g-1 , nearly doubling the capacity of commercially used cathodes and close to the limit for lithiated transition metal oxides. [8] Figure 1 lists the main development milestones of LMLO. In 1997 a novel material, LiCoO 2-Li 2 MnO 3 , was found by Numata et al., [9] a discovery that initiated intensive work on high energy density cathode materials. This group studied these materials intensively and demonstrated their cycling stability in the range of 3.0-4.3 V versus Li. [10] In 1999, Kalyani et al. reported that Li 2 MnO 3 can undergo electrochemical activation at potentials >4.5 V versus Li. [11] Dahn et al. described the charge compensation mechanism of LMLO, [12] and these cathodes were shown to provide high capacity at high operational voltage (>4.5 V). [13] In 2004, Thackeray et al. explored xLi 2 M′O 3-(1-x)LiMn 0.5 Ni 0.5 O 2 cathode materials with M′ = Zn, Ti, or Mn, concluding that Li 2 M′O 3 and LiMn 0.5 Ni 0.5 O 2 in these composite materials were integrated by short-range interactions. [14] The following Rechargeable lithium-ion batteries have become the dominant power sources for portable electronic devices, and are regarded as the battery technology of choice for electric vehicles and as potential candidates for grid-scale storage. Commercial lithium-ion batteries, after three decades of cell engineering, are approaching their energy density limits. Toward continually improving the energy density and reducing cost, Li-rich Mn-based layered oxide (LMLO) cathodes are receiving more and more attention due to their high discharge capacity and low cost. However, commercialization has been hampered by severe capacity and voltage decay, sluggish rate capability, and poor safety performance during charge/discharge cyc...

Abstract:The H 2 /air-fed proton exchange membrane fuel cell (PEMFC) has two major problems: cost and durability, which obstruct its pathway to commercialization. Cell reversal, which would create irreversible damage to the fuel cell and shorten its lifespan, is caused by reactant starvation, load change, low catalyst performance, and so on. This paper will summarize the causes, consequences, and mitigation strategies of cell reversal of PEMFC in detail. A description of potential change in the anode and cathode and the differences between local starvation and overall starvation are reviewed, which gives a framework for comprehending the origins of cell reversal. According to the root factor of cell starvation, i.e., fuel cells do not satisfy the requirements of electrons and protons of normal anode and cathode chemical reactions, we will introduce specific methods to mitigate or prevent fuel cell damage caused by cell reversal in the view of system management strategies and component material modifications. Based on a comprehensive understanding of cell reversal, it is beneficial to operate a fuel cell stack and extend its lifetime.