Gaoran Li

Strings of Porous Carbon Polyhedrons as Self-Standing Cathode Host for High-Energy-Density Lithium–Sulfur Batteries

Rational design of cathode hosts with high electrical conductivity and strong sulfur confinement is a great need for high-performance lithium-sulfur batteries. Herein, we report a self-standing, hybrid-nanostructured cathode host comprised of metal-organic framework (MOF)-derived porous carbon polyhedrons and carbon nanotubes (CNTs) for the significant improvement of both the electrode cyclability and energy density. The strong coupling of the intertwined CNTs and strung porous carbon polyhedrons as a binder-free thin film significantly enhances the long-range electronic conductivity and provides abundant active interfaces as well as robust electrode integrity for sulfur electrochemistry. Attributed to the synergistic combination of the CNTs and carbon polyhedrons, the obtained sulfur electrodes exhibit outstanding cyclability, an excellent high-rate response up to 10u2009C, and an ultra-high volumetric capacity of 960u2005Ahu2009L-1 .

Flexible and Binder-Free Hierarchical Porous Carbon Film for Supercapacitor Electrodes Derived from MOFs/CNT

Rational design of free-standing porous carbon materials with large specific surface area and high conductivity is a great need for ligh-weight suprecapacitors. Here, we report a flexible porous carbon film composed of metal-organic framework (MOF)-derived porous carbon polyhedrons and carbon nanotubes (CNTs) as binder-free supercapacitor electrode for the first time. Due to the synergistic combination of carbon polyhedrons and CNT, the obtained carbon electrode shows a specific capacitance of 381.2 F g-1 at 5 mV s-1 and 194.8 F g-1 at 2 A g-1 and outstanding cycling stability with a Coulombic effciency above 95% after 10000 cycles at 10 A g-1. The assembled aqueous symmetrical supercapacitor exhibits an energy density of 9.1 Wh kg-1 with a power density of 3500 W kg-1. The work opens a new way to design flexible MOF-based hierarchical porous carbon film as binder-free electrodes for high-performance energy storage devices.

B,N-Co-doped Graphene Supported Sulfur for Superior Stable Li–S Half Cell and Ge–S Full Battery

B,N-Co-doped graphene supported sulfur (S@BNG) composite is synthesized by using melamine diborate as precursor. XPS spectra illustrates that BNG with a high percentage and dispersive B, N (B = 13.47%, N = 9.17%) and abundant pyridinic-N and N-B/N═B bond, show strong interaction with Li2Sx proved by adsorption simulation experiments. As cathode for Li-S half cell, S@BNG with a sulfur content of 75% displays a reversible capacity of 765 mA h g-1 at 1 C even after 500 cycles (a low fading rate of 0.027% per cycle). Even at a high sulfur loading of 4.73 mg cm-2, S@BNG still shows a high and stable areal capacity of 3.5 mA h cm-2 after 48 cycles. When S@BNG composite as cathode combines with high performance lithiated Ge anode (discharge capacity of 1138 mA h g-1 over 1000 cycles at 1 C in half cell), the assembled Ge-S full battery exhibits a superior capacity of 530 mA h g-1 over 500 cycles at the rate of 1 C.

CNT-threaded N-doped porous carbon film as binder-free electrode for high-capacity supercapacitor and Li–S battery

A novel lightweight, free-standing, CNT-threaded nitrogen-doped porous carbon film (CNCF) has been synthesized as a binder-free electrode for supercapacitor and Li–S battery. The meticulous structural design of using CNT to thread the ZIF-8-derived porous carbon polyhedrons together endows the porous carbon thin film with nice flexibility, high surface area (645.2 m2 g−1), and hierarchical pore structure as well as good nitrogen doping (2.8 at%) and overall electrical conductivity. When used as binder-free electrode for a supercapacitor, the CNCF delivers a high specific capacitance of 340 F g−1 at 2 A g−1, long-term stability with a coulombic efficiency of 97.7% after 10u2006000 cycles at 20 A g−1, and high energy density of 21.1 W h kg−1 with a power density of 5000 W kg−1. It can also serve as an efficient sulfur host for the Li–S battery. The S@CNCF electrode exhibits a high discharge capacity of 926 mA h g−1 after 200 cycles at 1C, and 614 mA h g−1 after 1800 cycles with an ultra-low overall capacity decay of 0.02%/cycle with sulfur loading of 3 mg cm−2. Moreover, when the sulfur loading is increased to 6.9 mg cm−2, the electrode shows a high initial areal capacity of 7.3 mA h cm−2 and a volumetric capacity of 0.94 A h cm−3. This film holds promising potential for flexible or film-like high-energy storage systems.

Tuning Shell Numbers of Transition Metal Oxide Hollow Microspheres toward Durable and Superior Lithium Storage

Multishelled hollow structured transition metal oxides (TMOs) are highly potential materials for high energy density energy storage due to their high volumetric energy density, reduced aggregation of nanosized subunits, and excellent capacity and durability. However, traditional synthetic methods of TMOs generally require complicated steps and lack compositional/morphological adjustability. Herein, a general and straightforward strategy is developed to synthesize multishelled porous hollow microspheres, which is constituted of nanosize primary TMO particles, using metal acetate polysaccharide microspheres as the precursor. This universal method can be applied to design TMOs hollow spheres with tunable shell numbers and composition. The hierarchical porous quadruple-shelled hollow microspheres with nanosized Ni-Co-Mn oxide demonstrate an increased number of active sites, boosted rate capability, enhanced volumetric energy density, and showed great tolerance toward volume expansion upon cycling, thus exhibiting excellent Li+ storage capability with high specific capacity (1470 mAh g-1 at 0.2 A g-1 and 1073.6 mAh g-1 at 5.0 A g-1) and excellent cycle retention (1097 mAh g-1 after 250 cycles at 0.2 A g-1) among TMO anode materials for lithium-ion batteries.

Revisiting the Role of Polysulfides in Lithium–Sulfur Batteries

Intermediate polysulfides (Sn , where n = 2-8) play a critical role in both mechanistic understanding and performance improvement of lithium-sulfur batteries. The rational management of polysulfides is of profound significance for high-efficiency sulfur electrochemistry. Here, the key roles of polysulfides are discussed, with regard to their status, behavior, and their correspondingimpact on the lithium-sulfur system. Two schools of thoughts for polysulfide management are proposed, their advantages and disadvantages are compared, and future developments are discussed.

A scalable in situ surfactant-free synthesis of a uniform MnO/graphene composite for highly reversible lithium storage

A novel MnO/graphene composite, used as an anode for lithium ion intercalation, was prepared via an in situ surfactant-free facile method by taking advantage of the byproduct Mn ion in the conventional fabrication of graphene oxide. The as-fabricated lithium ion batteries exhibited a long-term stable reversible capacity (603 mA h g-1 after 350 cycles at 1 A g-1 based on the composite, hereinafter the same) and superior rate performance (400 mA h g-1 at 3 A g-1).

Stringed “tube on cube” nanohybrids as compact cathode matrix for high-loading and lean-electrolyte lithium–sulfur batteries

The rational design of cathode host materials is significant in fulfilling high-efficiency sulfur electrochemistry as well as boosting the energy density of lithium–sulfur (Li–S) batteries. Herein, we develop a stringed “tube on cube” nanohybrid (CPZC) with a ternary hierarchical architecture, which contains a fibrous carbon skeleton, highly porous carbon cube filler, and abundant CNT tentacles as an advanced matrix for sulfur electrodes. The as-developed CPZC delivers excellent conductivity, abundant active interfaces, and strong confinement to polysulfide, and thus is capable of significantly expediting the sulfur redox kinetics and promoting battery durability. The fabricated sulfur electrode achieves a superb rate capability up to 10C, outstanding cyclability over 2000 cycles, and more importantly, excellent performance under high a sulfur loading and sparing electrolyte with a high energy density of 348.8 W h kg−1 and 327.6 W h L−1 at the system level, which reveals its potential in promoting the practical application of Li–S batteries.

Highly Nitrogen-Doped Three-Dimensional Carbon Fibers Network with Superior Sodium Storage Capacity

Inspired by the excellent absorption capability of spongelike bacterial cellulose (BC), three-dimensional hierarchical porous carbon fibers doped with an ultrahigh content of N (21.2 atom %) (i.e., nitrogen-doped carbon fibers, NDCFs) were synthesized by an adsorption-swelling strategy using BC as the carbonaceous material. When used as anode materials for sodium-ion batteries, the NDCFs deliver a high reversible capacity of 86.2 mAh g-1 even after 2000 cycles at a high current density of 10.0 A g-1. It is proposed that the excellent Na+ storage performance is mainly due to the defective surface of the NDCFs created by the high content of N dopant. Density functional theory (DFT) calculations show that the defect sites created by N doping can strongly host Na+ and therefore contribute to the enhanced storage capacity.