Hard carbon has been extensively investigated as anode materials for high-energy lithium-ion batteries owing to its high capacity, long cycle life, good rate capability, and low cost of production. However, it suffers from a large irreversible capacity and thus low initial coulombic efficiency (ICE), which hinders its commercial use. Here, we developed a fast and controllable prelithiation method based on a chemical reaction using a lithium-containing reagent (1 M lithium biphenylide dissolved in tetrahydrofuran). The prelithiation extent can be easily controlled by tuning the reaction time. An SEI layer is formed during chemical prelithiation, and the ICE of prelithiated hard carbon in half-cell format can be increased to ∼106% in 30 s. When matched with a LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode, the full cell with the prelithiated hard carbon anode exhibits a much improved ICE (90.2 vs 75%) and cycling performance than those of the pristine full cell. This facile prelithiation method is proved to be a practical solution for the commercial application of hard carbon materials.

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SnO2 is an attractive anodic material for advanced lithium-ion batteries (LIBs). However, its low electronic conductivity and large volume change in lithiation/delithiation lead to a poor rate/cycling performance. Moreover, the initial Coulombic efficiencies (CEs) of SnO2 anodes are usually too low to build practical full LIBs. Herein, a two-step hydrothermal synthesis and pyrolysis method is used to prepare a SnO2/C nanocomposite, in which aggregated SnO2 nanosheets and a carbon network are well-interpenetrated with each other. The SnO2/C nanocomposite exhibits a good rate/cycling performance in half-cell tests but still shows a low initial CE of 45%. To overcome this shortage and realize its application in a full-cell assembly, the SnO2/C anode is controllably prelithiated by the lithium-biphenyl reagent and then coupled with a LiCoO2 cathode. The resulting full LIB displays a high capacity of over 98 mAh g–1 LCO in 300 cycles at 1 C rate.

Figure 3. Designing interconnected and stable pore structure: a) tomography image and skeleton of a thick electrode with interconnected pore structure. Reproduced with permission.

Electrochemical impedance spectroscopy provides information on the steady state of an electrochemical redox reaction and its kinetics. For instance, impedance is a very useful technique to investigate kinetics in batteries, such as diffusion processes or charge-transfer reaction dynamics during battery operation. Here, we summarize procedures for conducting reliable impedance measurements on a battery system, including cell configurations, readiness of a system for impedance testing, validation of the data in an impedance spectrum, deconvolution of electrochemical processes based on the distribution of relaxation time and equivalent circuit fitting of the impedance spectrum. The aim of this paper is to discuss key parameters for accurate and repeatable impedance measurements of batteries.

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The main bottlenecks for the application of polymer electrolyte fuel cells in electric vehicles are the high cost and the inferior performance of Nafion at high temperatures above 80 °C. In this work, composite membranes made by infiltrating Nafion in various PTFE fibrous substrates were prepared, characterized, and assessed for a single fuel cell performance. Prepared by a simple dip-coating method, the composite membrane exhibited satisfactory mechanical strength and thermal stability with the incorporation of a PTFE backbone, which can suppress the swelling of the Nafion component. The durability of the composite membranes in terms of through-plane conductivity after boiling at 120 °C was comparable to that of Nafion117. Moreover, the Nafion/PTFE membrane was able to achieve higher through-plane conductivity than Nafion117 at higher temperatures of 100 °C, indicating potential application in high temperature condition.

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