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Silicon (Si) is a promising anode material for LIBs due to its high theoretical gravimetric capacity of 3570 mAh g−1, which is about ten times higher than that of graphite. However, the large volume expansion of Si during lithiation gives rise to non-trivial mechanical challenges and constraints which hinder widespread commercial adoption. In particular, electrode cracking and delamination destroy the intrinsic electrical connectivity in the Si electrodes, leading to rapid capacity degradation upon cycling. Herein, we demonstrate a novel approach of capping Si thin-film electrodes with a high strength polyimide by electro-spraying to overcome the pulverization and mechanical issues during cycling. The polyimide layer provides mechanical support to the Si thin-film and maintains its capacity during cycling, with a high capacity of 2610 mAh g−1at 100 mA g−1and no capacity loss after 300 cycles at 3500 mA g−1. Furthermore, in situdilatometry tests reveal that the polyimide capping layer enables reversible electrode thickness change during lithiation and de-lithiation, thus improving the cycling performance. This work provides a practical manufacturing strategy for commercializing silicon-based electrode films.

Selenium (Se)-based materials for sodium (ion) batteries are currently attracting extensive attentions owing to their fast kinetics and excellent cyclability; at the same time, achieving high Se content, which is crucial to maintain the competitive edge over other kinds of electrode materials, still remains a challenge. We developed a confined annealing method which allows us to convert pristine metal-organic frameworks (MOFs) directly into selenium/selenide/carbon composites. It is a simultaneous process of carbonization, selenization and Se vapor deposition, and the combination of elemental Se and selenide results in a record-high Se content of 76 wt%, enhanced capacity and rate capability (490 and 384 mA h g−1at 0.1 and 2.0 A g−1) exceeding most documented Se-based materials. The produced composites also exhibit excellent cycle stability (no decay for 700 cycles at 2 A g−1), which is correlated to dominant capacitive charge transport mode and the MOF-derived robust structure. Our work not only offers a proof of concept that Se content can be maximized by confining Se through both vapor deposition and chemical bonding with transition metals, but also demonstrates a general and green selenization approach without using any toxic or flammable chemicals. The introduced method will probably prevail for its wide applicability on various metal-containing precursors, and even be expanded to the fabrication of sulfur- and phosphor-based composites.

Antimony-based electrodes are promising as fast charging anodes for lithium-ion batteries because their operating potential is about 0.8 V vs. Li/Li+, far away from the plating potential of Li. However, their capacity decays fast due to large volume expansion, the issue which has often been addressed through the use of nano-sized materials. Herein, we utilize an ion-dipole interaction between polyimide and carboxymethyl cellulose which suppresses particle cracking and holds the particle together to enable antimony anodes utilizing micron-sized Sb particles for high rate applications. Sb anode with 9.4% polyimide coating exhibits a high reversible capacity of 580 mAh g−1at 1 A g−1with excellent cycle performance. The rate performance of the electrode can be further improved by adding 5% acetylene black during the polyimide coating process. Even at a current rate of 20 C (13.2 A g−1), a highly reversible capacity of 380 mAh g−1can be obtained. The superior high-rate capability and excellent stability of Sb anodes are further verified by full-cell tests with LiFePO4cathodes.

Interface engineering on 2D layered nanomaterials plays pivotal roles in achieving novel properties and superior device performance. In this work, hierarchical nanotubes consisting of 2D monolayer MoS2and carbon (MoS2:C) interoverlapped superstructure nanosheets have been synthesized, in which the MoS2and carbon layers are alternately sandwiched. The hierarchical architectures assembled from the MoS2:C superstructures are beneficial for: (i) providing substantially expanded (002) interlayer spacing (0.98nm) of 2H-MoS2which facilitates fast Na+insertion/extraction reaction kinetics, (ii) improving electrical conductivity of MoS2by carbon monolayer insertion with ideal heterointerface contact, (iii) preventing aggregation of MoS2nanosheets, and (iv) accommodating volume change upon sodiation/desodiation. The superstructure nanotubes are demonstrated as a robust anode material for sodium storage with superior electrochemical performance. They deliver a high rate-capability and maintain discharge capacities of 295 and 187mAhg−1at high current densities of 10.0 and 20.0Ag−1, respectively. Furthermore, they show durable cycling life (capacity retention of 101.3%, 108.2% and 107.8% after 200 cycles at current densities of 0.2, 0.5 and 1.0 Ag−1, respectively, in comparison to those of the 2ndcycles), and an initial Coulombic efficiency as high as 84%. The MoS2:C superstructure nanotubes perform among the best of current MoS2-based electrode materials.

Co3O4nanoparticles are grown on nitrogen modified microwave exfoliated graphite oxide (NMEG) with weight ratio controlled from 10% to 70%. Electrochemical performance reveals that the obtained Co3O4/NMEG composite as Li-ion battery anode exhibits improved cycle stability, excellent reversible capacity, high current rate performance, and reduced irreversible capacity loss in the initial cycle compared to pure Co3O4without graphene or Co3O4on thermally reduced graphene oxide (tRG-O). The 70%Co3O4/NMEG composite has initial irreversible capacity of 230mAhg−1(first cycle efficiency of 77%), and 910mAhg−1of capacity is retained after 100 cycles. The 70%Co3O4/tRG-O delivers a reversible capacity of 750±20mAhg−1, and the irreversible capacity loss during the first cycle is 700±20mAhg−1. Nitrogen functional groups in NMEG, especially pyridinic and pyrrolic N are advantageous for the Co3O4growth. Furthermore, the N modification is effective in reducing the oxygen content of chemically prepared graphene and hence is good for Co3O4dispersion and the amelioration of first cycle efficiency, demonstrating the potential of NMEG based composite as high performance Li-ion battery anode materials.

Structure of Li2MnO3during charge and discharge is studied by x-ray diffraction, Raman spectroscopy and x-ray absorption spectroscopy (XAS). During electrochemical delithiation, development of a local spinel-like structure and an increase in disordering of Mn in Li2MnO3is observed from Raman spectroscopy and XAS, respectively. However, the charge-discharge curves show a sloping profile, which is associated with Mn atoms in the transition metal layer. Upon cycling, plateaus develop in the 3 and 4 V regions, suggesting transformation of Li2MnO3to a spinel structure. The formation of spinel phase is linked to Mn re-arrangement in the lattice and lowering of oxygen content, as indicated by results of Li-Mn-O compounds made by varying Li/Mn ratio during synthesis and by chemically (acid treatment) extracting Li from Li2MnO3. Our results suggest the better cycle performance of Li-excess materials with a solid solution of Li2MnO3-LiMnO2is due to stabilization of the Li2MnO3structure by addition of a layered component into the structure.

Li2MnO3is shown to be electrochemically active, with a maximum charge capacity of ∼350mAh∕gand a discharge capacity of ∼260mAh∕gat 25°C. A total of 1moleof Li can be extracted from Li[Li1∕3Mn2∕3]O2, and the first cycle efficiency is ∼66%regardless of state of charge. Larger charge-discharge capacity is obtained from materials with smaller particle size and larger amount of stacking faults. Composition and structural analyses indicate that Li are removed from both the Li and transitional metal layers of the material during charging. Results from X-ray-absorption fine-structure measurements suggest that the valence of Mn remains at 4+during charging but is reduced during discharging. Charging is accompanied by gas generation: at 25°C, oxygen is the main gas detected, and the total amount accounts for ∼1∕8moleof O2generation from Li[Li1∕3Mn2∕3]O2. At an elevated temperature, amount of CO2increases due to electrolyte decomposition. Li2MnO3shows poor cycle performance, which is attributed to phase transformation and low charge-discharge efficiency during cycling. Low first-cycle efficiency, gas generation, and poor cycle performance limit the usage of Li2MnO3in practical batteries.

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