Xia Wang

Engineering Hybrid between MnO and N-Doped Carbon to Achieve Exceptionally High Capacity for Lithium-Ion Battery Anode

A facile and low-cost strategy is demonstrated for preparing MnO/C-N hybrid, in which the MnO nanoparticles chemically combine with N-doped C by Mn-N bonding to achieve the hybridization of MnO with N-doped C. When served as an anode in lithium ion batteries (LIBs), the resultant hybrid manifested high capacity, excellent cyclability, and superior rate capability. A lithium storage capacity of 1699 mAh g(-1) could be obtained at 0.5 A g(-1) after 170 discharge-charge cycles. Even at a current density up to 5 A g(-1), a high reversible capacity (907.8 mAh g(-1)) can be retained after 400 cycles. The excellent lithium storage performance of the MnO/C-N hybrid can be ascribed to the synergetic effects of several factors including the unique hybrid structure, the N-doping and the chemical bonding of MnO and N-doped C.

In Situ Encapsulation of Germanium Clusters in Carbon Nanofibers: High‐Performance Anodes for Lithium‐Ion Batteries

Alloyed anode materials for lithium-ion batteries (LIBs) usually suffer from considerable capacity losses during charge-discharge process. Herein, inu2005situ-grown germanium clusters are homogeneously encapsulated into porous nitrogen-doped carbon nanofibers (N-CNFs) to form Ge/N-CNFs hybrids, using a facile electrospinning method followed by thermal treatment. When used as anode in LIBs, the Ge/N-CNFs hybrids exhibit excellent lithium storage performance in terms of specific capacity, cycling stability, and rate capability. The excellent electrochemical properties can be attributed to the unique structural features: the distribution of the germanium clusters, porous carbon nanofibers, and Geuf8ffN chemical bonds all contribute to alleviating the large volume changes of germanium during the discharge-charge process, while at same time the unique porous N-CNFs not only increase the contact area between the electrode and the electrolyte, but also the conductivity of the hybrid.

Germanium Quantum Dots Embedded in N‐Doping Graphene Matrix with Sponge‐Like Architecture for Enhanced Performance in Lithium‐Ion Batteries

Germanium quantum dots embedded in a nitrogen-doped graphene matrix with a sponge-like architecture (Ge/GN sponge) are prepared through a simple and scalable synthetic method, involving freeze drying to obtain the Ge(OH)4 /graphene oxide (GO) precursor and subsequent heat reduction treatment. Upon application as an anode for the lithium-ion battery (LIB), the Ge/GN sponge exhibits a high discharge capacity compared with previously reported N-doped graphene. The electrode with the as-synthesized Ge/GN sponge can deliver a capacity of 1258u2005mAhu2009g(-1) even after 50 charge/discharge cycles. This improved electrochemical performance can be attributed to the pore memory effect and highly conductive N-doping GN matrix from the unique sponge-like structure.

Lithium Storage in Microstructures of Amorphous Mixed-Valence Vanadium Oxide as Anode Materials.

Constructing three-dimensional (3u2009D) nanostructures with excellent structural stability is an important approach for realizing high-rate capability and a high capacity of the electrode materials in lithium-ion batteries (LIBs). Herein, we report the synthesis of hydrangea-like amorphous mixed-valence VOx microspheres (a-VOx MSs) through a facile solvothermal method followed by controlled calcination. The resultant hydrangea-like a-VOx MSs are composed of intercrossed nanosheets and, thus, construct a 3u2009D network structure. Upon evaluation as an anode material for LIBs, the a-VOx MSs show excellent lithium-storage performance in terms of high capacity, good rate capability, and long-term stability upon extended cycling. Specifically, they exhibit very stable cycling behavior with a highly reversible capacity of 1050u2005mAu2009hu2009g(-1) at a rate of 0.1u2005Au2009g(-1) after 140u2005cycles. They also show excellent rate capability, with a capacity of 390u2005mAu2009hu2009g(-1) at a rate as high as 10u2005Au2009g(-1) . Detailed investigations on the morphological and structural changes of the a-VOx MSs upon cycling demonstrated that the a-VOx MSs went through modification of the local Vuf8ffO coordinations accompanied with the formation of a higher oxidation state of V, but still with an amorphous state throughout the whole discharge/charge process. Moreover, the a-VOx MSs can buffer huge volumetric changes during the insertion/extraction process, and at the same time they remain intact even after 200u2005cycles of the charge/discharge process. Thus, these microspheres may be a promising anode material for LIBs.

Enhancement of Lithium Storage Performance of Carbon Microflowers by Achieving a High Surface Area

High-surface-area, nitrogen-doped carbon microflowers (A-NCFs-4) assembled from porous nanosheets are prepared in a three-step process: soft-templating self-assembly, thermal decomposition, and KOH activation. The hydrazine hydrate used in our experiment serves not only as a structure-directing agent, but also as a nitrogen source. The resultant A-NCFs-4 has a hierarchical porous structure and its specific surface area is as high as 2309u2005m(2) u2009g(-1). When used as anode, it exhibits a reversible capacity as high as 807u2005mAhu2009g(-1) at 300u2005mAu2009g(-1) after 100u2005cycles, and an excellent rate capability of 200u2005mAhu2009g(-1) at a high current density of 8u2005Au2009g(-1). Compared with unactivated counterpart, A-NCFs-4 exhibits a significantly improved lithium storage capacity and rate capability; this can be attributed to its unique structural characteristics and high surface area. The hierarchical micro-/mesopore structure, high surface area, and nitrogen doping of A-NCFs-4 could guarantee fast mass transport for lithium species, enhance the A-NCFs-4/electrolyte contact area, shorten the lithium-ion diffusion length, and accommodate strain induced by volume changes during the electrochemical reaction. The results indicate that the as-prepared A-NCFs-4 could be a promising candidate as a high-performance anode for lithium-ion batteries.