Zixia Lin

Activated carbon with ultrahigh specific surface area synthesized from natural plant material for lithium–sulfur batteries

Porous activated carbon with a ultrahigh specific surface area (3164 m2 g−1) and large pore volume (1.88 cm3 g−1) was prepared from waste litchi shells with channel-like macropores via a KOH activation method. The macroporous structure of litchi shells is believed to be conducive to distribute the activation agent, which enables sufficient activation. The as-prepared activated carbon was developed as a conducting framework for lithium–sulfur battery cathode materials. The resulting activated carbon/sulfur composite cathode possesses a high specific capacity, good rate capability, and long-term cycling performance. At 200 mA g−1 current density, the initial discharge capacity of the activated carbon/sulfur composite cathode with 60 wt% sulfur content is 1105 mA h g−1. At a current density of 800 mA g−1, the activated carbon/sulfur composite cathode shows 51% capacity retention over 800 cycles with a fade rate of 0.06% per cycle. The coulombic efficiency of the cell remains at approximately 95%. By adding LiNO3 in the electrolyte, the activated carbon/sulfur composite electrode tested at 800 mA g−1 shows a high coulombic efficiency (>99%). The activated carbon/sulfur composites exhibited similar capacity value and cycling trends with an increase in sulfur content from 60% to 68%. The good electrochemical performance can be attributed to the excellent structural parameters of the activated carbon. The ultrahigh specific surface area and large pore volume not only enhances the sulfur content but also ensures dispersion of elemental sulfur in the conducting framework, thereby improving sulfur utilization. The small nanopores of the activated carbon can effectively inhibit the diffusion of polysulfides during the charge/discharge process.

Flexible cathodes and multifunctional interlayers based on carbonized bacterial cellulose for high-performance lithium-sulfur batteries

A three-dimensional (3D) carbonaceous aerogel derived from sustainable bacterial cellulose (BC) is introduced as a flexible framework for sulfur in lithium–sulfur batteries. The 3D carbonized BC (CBC) with highly interconnected nanofibrous structure exhibits good electrical conductivity and mechanical stability. The intrinsic macroporous structure of CBC contributes to a high sulfur loading of 81 wt%. Microstructure and morphology characterization results demonstrate that the sulfur species wrapped around CBC nanofibers are well dispersed. Even at such a high loading, the S/CBC composite still contains sufficient free space to accommodate the volume expansion of sulfur during lithiation. Furthermore, with an ultralight CBC interlayer inserted between the sulfur cathode and separator, significant improvement is achieved in active material utilization, cycling stability, and coulombic efficiency. The CBC interlayer can provide an extra conductive framework and adsorb migrating polysulfides to a certain degree. The CBC interlayer can also act as an additional collector for sulfur and thus could prevent the over-aggregation of insulated sulfur on the cathode surface. The good electrochemical performance reported in this work can be ascribed to the flexible 3D-interconnected nanostructure of the carbon framework and the rational design of battery configuration.

Mesoporous NiO with a single-crystalline structure utilized as a noble metal-free catalyst for non-aqueous Li–O2 batteries

Mesoporous NiO nanosheets with a single-crystalline structure were investigated as an oxygen electrode catalyst in a non-aqueous Li–O2 battery. The recharge voltage plateau achieved for the NiO-based Li–O2 battery was ca. 3.95 V, ca. 200 mV negatively shifted compared with that for β-Ni(OH)2 and acetylene black. The reaction mechanism during the charge process for the NiO-based Li–O2 battery was intensively researched. The results of X-ray photoelectron spectroscopy characterization indicated that Li2O2 and Li2CO3 were formed during the discharge process, which can be decomposed after recharge. These demonstrated that the NiO nanosheet exhibited a good activity for the decomposition of Li2O2 and Li2CO3. Furthermore, the results of the gas chromatography-mass spectrometry test reflected two steps of the recharge process, i.e., the oxidation of Li2O2 when the potential was below 4.0 V and the decomposition of Li2O2 and Li2CO3 when the potential was above 4.0 V. Moreover, no obvious performance decay was observed in the NiO-based battery even after 40 cycles when the capacity was limited to 500 mA h g−1, indicating an impressive cycling performance.

Mesoporous iron oxide directly anchored on a graphene matrix for lithium-ion battery anodes with enhanced strain accommodation

A continuous mesoporous iron oxide nanofilm was directly formed on graphene nanosheets through the in situ thermal decomposition of Fe(NO3)3·9H2O and was anchored tightly on the graphene surface. The lithiation-induced strain was naturally accommodated, owing to the constraint effect of graphene and the mesoporous structure. Hence, the pulverization of the iron oxide nanofilm was effectively prevented.

Activated graphene with tailored pore structure parameters for long cycle-life lithium–sulfur batteries

Activated graphene (AG) with various specific surface areas, pore volumes, and average pore sizes is fabricated and applied as a matrix for sulfur. The impacts of the AG pore structure parameters and sulfur loadings on the electrochemical performance of lithium-sulfur batteries are systematically investigated. The results show that specific capacity, cycling performance, and Coulombic efficiency of the batteries are closely linked to the pore structure and sulfur loading. An AG3/S composite electrode with a high sulfur loading of 72 wt.% exhibited an excellent long-term cycling stability (50% capacity retention over 1,000 cycles) and extra-low capacity fade rate (0.05% per cycle). In addition, when LiNO3 was used as an electrolyte additive, the AG3/S electrode exhibited a similar capacity retention and high Coulombic efficiency (∼98%) over 1,000 cycles. The excellent electrochemical performance of the series of AG3/S electrodes is attributed to the mixed micro/mesoporous structure, high surface area, and good electrical conductivity of the AG matrices and the well-distributed sulfur within the micro/mesopores, which is beneficial for electrical and ionic transfer during cycling.

Mango stone-derived activated carbon with high sulfur loading as a cathode material for lithium–sulfur batteries

A set of mango stone (MS)-derived activated carbons with tunable pore structure parameters have been synthesized via a KOH activation procedure. The maximum specific surface area of 3334 m2 g−1 and pore volume of 2.17 cm3 g−1 are obtained for the material which is pre-carbonized at 500 °C and treated with a KOH/char mass ratio of 4 (a-MSs-500-4). Given the large pore volume of the resultant a-MSs-500-4 activated carbon, a high sulfur loading of up to 71 wt% can be achieved (a-MSs-500-4/71). When applied in a lithium–sulfur battery, the a-MSs-500-4/71 composite cathode exhibits 64% capacity retention over 500 cycles at 800 mA g−1 and 45% capacity retention over 1000 cycles at 1600 mA g−1, indicating excellent long-term cycling performance. Moreover, after 1 wt% LiNO3 is introduced as the electrolyte additive, the average coulombic efficiency of the electrode is as high as approximately 99%.

Fabrication of a reversible SnS2/RGO nanocomposite for high performance lithium storage

SnS2/graphene (SnS2/G) composites have been explored extensively as a promising candidate for Lithium Ion Battery (LIB) anodes in recent years. Previously, the SnS2 conversion/reduction step of the reaction mechanism is generally believed to be irreversible or only partially reversible, which severely underestimates the theoretical capacity of SnS2. In this work, SnS2 nanoparticles have been successfully stacked on reduced graphene oxide (RGO) via a facile and effective solvothermal method using ethylene glycol as a chelant. The SnS2/graphene nanocomposite retained many of the original 2D characteristics of the graphene nanosheets. As a result, Li+ storage properties were significantly improved. The SnS2/RGO nanocomposites show a higher storage capacity of 939.0 mA h g−1 after 30 cycles at a current density of 0.1 A g−1, and a long-term cycle capacity of 615.5 mA h g−1 even after 200 cycles at 1 A g−1. The superior cycling stability of the SnS2/RGO electrode is attributed to greater reversibility in the initial conversion reaction, ascribed to the presence of the Sn nanoparticles.

In situ growth of NiO nanoparticles on graphene as a high-performance anode material for lithium-ion battery anodes with enhanced strain accommodation

Nickel oxide (NiO) nanoparticles were directly formed on graphene nanosheets through in situ thermal decomposition of Ni(NO3)2·6H2O and were anchored tightly on the graphene surface. During the charge–discharge process, graphene nanosheets served as a three-dimensional conductive network for the NiO nanoparticles. The lithiation-induced strain was naturally accommodated because of the constraint effect of graphene. Thus, pulverization of NiO nanoparticles was effectively prevented.

Influence of the pore structure parameters of mesoporous anatase microspheres on their performance in lithium-ion batteries

Monodisperse mesoporous anatase microspheres were prepared by a combination of sol–gel and liquid–crystal template methods. With the change in annealing temperature, the pore structure parameters of samples were regulated. The influence of pore structure parameters on lithium-ion battery performance was systematically investigated. Results of electrochemical test and analysis demonstrated that the pore structure parameters significantly influenced the specific capacity, charging and discharging curves, rate capability, and cycle performance of the batteries. The first irreversible capacity increased with increased specific surface area. Materials with larger specific surface area showed better rate capability. When the average pore size was too small, the transport of Li+ in the electrolyte was impeded, which affected the rate capability of the materials. Based on the charging and discharging curves, the capacity of the plateau section corresponding to lithium insertion/extraction ions in the interstitial octahedral sites of anatase became smaller with increased specific surface area. By contrast, the capacity of the oblique line section corresponding to the Li+ insertion/extraction into/from the surface layer of anatase became larger. The pore volume influenced the cycling stability.

Interweaving of multilevel carbon networks with mesoporous TiO2 for lithium-ion battery anodes

Mesoporous TiO2 interwoven with multilevel carbon networks was obtained by in situ self-assembly of TiO2 and P123 micelles within the nanospace of thermally exfoliated graphene. The nanocomposite exhibited excellent capacity retention and good rate capability as a material for lithium-ion battery anodes.