Charging lithium ion battery cathode materials such as LiCoO2 to a higher voltage may simultaneously enhance the specific capacity and average operating voltage and thus improve the energy density. However, battery cycle life is compromised in high voltage cycling due to lattice instability and undesired oxidation of electrolyte. Cathode solid-electrolyte interphase (SEI), or cathode-electrolyte interphase (CEI), in situ formed at the cathode–electrolyte interface under high voltage, is critically important in understanding the cathode degradation process and crucial in improving high voltage cycle stability. Here we present in situ atomic force microscopy (AFM) investigation of CEI on LiCoO2 at high voltage. The formation of CEI is only observed at the LiCoO2 edge plane, not at the basal plane. The thin layer of Al2O3 coating completely suppresses the formation of CEI at the edge planes, and is shown to significantly improve coin cell high voltage cycle stability.Keywords: cathode electrolyte interphase (CEI); in situ atomic force microscopy; lithium cobalt oxide (LiCoO2); lithium ion battery; solid-electrolyte interphase (SEI);

•A mild reaction was adopted to prepare MnO2-CNT with fewer defects on the CNT.•The electrode exhibited excellent rate performance at high areal density.•The electrode areal capacitance reached 1.0 F cm−2 at 0.2 A g−1 (1.28 mA cm−2).•The electrode power density: 45.2 kW kg−1, energy density: 16.7 Wh kg−1.Practical supercapacitor devices require high areal capacitance and areal power density, and thus demand high utilization of active material and good rate performance under high areal mass loading. However, ion transport in high-mass-loading electrodes can be a challenge, which leads to deteriorate specific capacitance and rate performance. In this paper, a well-dispersed porous MnO2-carbon nanotube (CNT) composite was prepared for use as a supercapacitor electrode material. The small MnO2 nanoparticles and porous CNT network facilitated fast electron/ion transfer kinetics in the electrode. With a mass loading as high as 6.4 mg cm−2 on the electrode, the MnO2-CNT composite exhibited an excellent areal capacitance of 1.0 F cm−2 at 0.2 A g−1 (1.28 mA cm−2), with a retention of 77% even at a high current density of 20 A g−1 (128 mA cm−2). The electrode exhibited a high power density of 45.2 kW kg−1 (0.29 W cm−2) while maintaining a reasonable energy density of 16.7 Wh kg−1 (106 μWh cm−2). No apparent fading was observed even after 3000 charge/discharge cycles at 1 A g−1. This porous and evenly distributed MnO2-CNT composite has great potential for practical applications in supercapacitors.

A high rate capability is a primary requirement for an electric double-layer capacitor (EDLC) in practical applications, which is mainly governed by the ionic diffusion rate. Construction of the electrode structure with proper paths for the rapid transport of ions is an efficient method to facilitate the diffusion of ions in the electrode. In this study, we prepared multi-walled carbon nanotube microspheres (MWNTMS) with a stable porous structure via the spray drying method. The MWNTMS act as a local electrolyte micro-reservoir and provide stable ion transport paths in the EDLC electrode, which will facilitate the access of the electrode to the electrolyte and accelerate the diffusion rate of the ions. Using only MWNTMS as active materials, an areal capacitance of 105 mF/cm2 at 30 A/g is observed at an areal density of 7.2 mg/cm2. When the MWNTMS are combined with reduced graphene oxides (rGO) to form an rGO-MWNTMS hybrid electrode with an areal density of 3.0 mg/cm2, a high areal capacitance of 136 mF/cm2 at 100 A/g is observed. This rGO-MWNTMS-based EDLC presents a high areal power density of 1540 mW/cm2. These favorable results indicate that MWNTMS are promising materials for applications in high power supercapacitors.

We report a sulfur–amine chemistry-based method to prepare multi-walled carbon nanotube–sulfur (MWNT–S) composites in a highly efficient and quantitative manner. The resulting MWNT–S composites exhibit excellent cycling stability at up to 400 cycles, with high sulfur loading. Developing this method also increases the number of research routes that could be pursued with respect to Li–S batteries.

The solid electrolyte interphase (SEI) that forms on electrodes largely defines the performances of lithium ion batteries (LIBs), such as cycling performance, shelf life, and safety. Additives in the electrolyte can modify the properties of the SEI and thus efficiently improve the performances of LIBs. However, the effects of additives on the mechanical properties, structure, and stability of the SEI have rarely been studied directly. In this paper, we report the influence of vinylene carbonate (VC) and lithium bis(oxalate)borate (LiBOB) additives on the mechanical properties of SEI films formed on MnO electrodes using atomic force microscopy (AFM) and force spectroscopy. The results show that the SEI formed from VC additive is thick and soft and partially decomposes upon charging. LiBOB forms thin, stiff, and electrochemically stable SEI films, but the stiff SEI may not be favorable for adapting the volume change of the electrodes. The VC and LiBOB mixed additive combines the advantages of the two components and produces stable SEI with moderate thickness and stiffness. This work also demonstrates that the AFM–force spectroscopy method is effective in investigating the structure and mechanical properties of SEI films.

Solid electrolyte interphase (SEI) is an in situ formed thin coating on lithium ion battery (LIB) electrodes. The mechanical property of SEI largely defines the cycling performance and the safety of LIBs but has been rarely investigated. Here, we report quantitatively the Young’s modulus of SEI films on MnO anodes. The inhomogeneity of SEI film in morphology, structure, and mechanical properties provides new insights to the evolution of SEI on electrodes. Furthermore, the quantitative methodology established in this study opens a new approach to direct investigation of SEI properties in various electrode materials systems.

We report a sulfur–amine chemistry-based method to prepare multi-walled carbon nanotube–sulfur (MWNT–S) composites in a highly efficient and quantitative manner. The resulting MWNT–S composites exhibit excellent cycling stability at up to 400 cycles, with high sulfur loading. Developing this method also increases the number of research routes that could be pursued with respect to Li–S batteries.