Xiaoxiong Xu

A 3D porous architecture of Si/graphene nanocomposite as high-performance anode materials for Li-ion batteries

A 3D porous architecture of Si/graphene nanocomposite has been rationally designed and constructed through a series of controlled chemical processes. In contrast to random mixture of Si nanoparticles and graphene nanosheets, the porous nanoarchitectured composite has superior electrochemical stability because the Si nanoparticles are firmly riveted on the graphene nanosheets through a thin SiOx layer. The 3D graphene network enhances electrical conductivity, and improves rate performance, demonstrating a superior rate capability over the 2D nanostructure. This 3D porous architecture can deliver a reversible capacity of ∼900 mA h g−1 with very little fading when the charge rates change from 100 mA g−1 to 1 A g−1. Furthermore, the 3D nanoarchitechture of Si/graphene can be cycled at extremely high Li+ extraction rates, such as 5 A g−1 and 10 A g−1, for over than 100 times. Both the highly conductive graphene network and porous architecture are considered to contribute to the remarkable rate capability and cycling stability, thereby pointing to a new synthesis route to improving the electrochemical performances of the Si-based anode materials for advanced Li-ion batteries.

MoS2 nanoflowers consisting of nanosheets with a controllable interlayer distance as high-performance lithium ion battery anodes

MoS2 nanoflowers consisting of nanosheets are synthesized by a one-step hydrothermal method. The interlayer distances of the MoS2 nanosheets, accompanied with the changes of crystallinity, defects, specific surface areas as well as the thickness of the MoS2 nanosheets, can be well controlled via simply altering hydrothermal reaction temperatures. The effect of interlayer distances on the lithium storage capability for lithium ion batteries is investigated. The results show that MoS2 synthesized under 200 °C with an interlayer distance of 0.65 nm exhibit the highest lithium storage capacity and the best rate capability, showing a high discharge capacity of 814.2 mA h g−1 at 100 mA g−1 after 50 cycles and as high as 652.2 mA h g−1 and 547.3 mA h g−1 at current densities of 1 A g−1 and 2 A g−1 at 25 °C, respectively. The excellent lithium storage properties of the resultant MoS2 nanoflowers are attributed to its controllable optimized interplanar distance with good crystallinity, appropriate surface area and defects as well as thickness of the nanosheets.

Direct observation of lithium-ion transport under an electrical field in LixCoO2 nanograins.

The past decades have witnessed the development of many technologies based on nanoionics, especially lithium-ion batteries (LIBs). Now there is an urgent need for developing LIBs with good high-rate capability and high power. LIBs with nanostructured electrodes show great potentials for achieving such goals. However, the nature of Li-ion transport behaviors within the nanostructured electrodes is not well clarified yet. Here, Li-ion transport behaviors in LixCoO2 nanograins are investigated by employing conductive atomic force microscopy (C-AFM) technique to study the local Li-ion diffusion induced conductance change behaviors with a spatial resolution of ~10 nm. It is found that grain boundary has a low Li-ion diffusion energy barrier and provides a fast Li-ion diffusion pathway, which is also confirmed by our first principles calculation. This information provides important guidelines for designing high performance LIBs from a point view of optimizing the electrode material microstructures and the development of nanoionics.

All-solid-state lithium batteries with inorganic solid electrolytes: Review of fundamental science

The scientific basis of all-solid-state lithium batteries with inorganic solid electrolytes is reviewed briefly, touching upon solid electrolytes, electrode materials, electrolyte/electrode interface phenomena, fabrication, and evaluation. The challenges and prospects are outlined as well.

High-Performance Silicon/Carbon/Graphite Composites as Anode Materials for Lithium Ion Batteries

Silicon/carbon and silicon/carbon/graphite composites have been synthesized at room temperature using concentrated H 2 SO 4 as a dehydration agent. As a ductile matrix, the novel amorphous carbon obtained from the dehydration process could effectively buffer the volume change of silicon particles during discharge-charge cycling. The introduction of graphite in the silicon/carbon composite further improved the cycling performance. The composite with 30 wt % of amorphous carbon replaced by graphite demonstrated a stable capacity of 712.8 mAh g -1 and a high capacity retention ratio of 84.1% at 0.1 C over 50 cycles, suggesting it is a favorable candidate as anode material for lithium-ion batteries.

Tantalum oxide nanomesh as self-standing one nanometre thick electrolyte

Tantalum oxide (TaO3) nanosheets coated on the surface of a LiCoO2 cathode decrease its interfacial resistance in a solid-state battery by two orders of magnitude. Since the interfacial resistance is rate-determining in the solid-state system, the interfacial structure of the nanosheet is anticipated to pave the way for realising high-performance solid-state lithium batteries. The reduction in the interfacial resistance also strongly suggests that the TaO3 nanosheet is a self-standing solid electrolyte layer with an ultimate thinness of 1 nm. It has a wide band gap and a mesh structure with openings that are almost the same in size as the lithium ion, which prevents electronic conduction and allows the penetration of lithium ions, respectively.

Quality control of epitaxial LiCoO 2 thin films grown by pulsed laser deposition

Thin films of c -axis-oriented LiCoO 2 were epitaxially grown by pulsed laser deposition (PLD). The ablation laser conditions greatly affect the crystal quality of the epitaxial LiCoO 2 thin films. In addition, high-quality LiCoO 2 thin films were found to grow without any impurity phases under relatively low oxygen partial pressure, although high pressure had been often selected to suppress the formation of Co 3 O 4 with a lower valence state as an impurity. This result clearly indicates that the ablation laser conditions are an essential growth parameter, and that composition control is indispensable to grow high-quality complex compound thin films by PLD.

An advanced construction strategy of all-solid-state lithium batteries with excellent interfacial compatibility and ultralong cycle life

The inferior cycle performance of All-solid-state lithium batteries (ASSLBs) resulting from the low mixed ionic and electronic conductivity in the electrodes, as well as the large interfacial resistance between the electrodes and the electrolyte need to be overcome urgently for commercial applications. Here, an advanced cell construction strategy has been proposed, in which a cohesive and highly conductive poly(oxyethylene) (PEO)-based electrolyte is employed both in the cathode layer and in the interface of the electrolyte/anode, leading to an ASSLB with superior interfacial contact between the electrolyte and the electrodes, and forming a three-dimensional ionic conductive network in the cathode layer. Especially, the NASICON-type ionic conductor covered with the PEO-based polymer, integrating the advantages of an inorganic electrolyte and organic electrolyte, presents an enhanced electrochemical stability and an excellent compatibility with the Li electrode. Consequently, the ASSLBs of LiFePO4 (LFP)/Li with this advanced construction strategy exhibit excellent interfacial compatibility, ultralong cycle life and high capacity, i.e., a reversible discharge capacity maintained at 127.8 mA h g−1 for the 1000th cycle at 1C with a retention of 96.6%, and an initial discharge capacity of 153.4 mA h g−1 with a high retention of 99.9% after 200 cycles at 0.1C. Besides, the high-voltage monopolar stacked batteries with a bipolar structure can be fabricated conveniently, showing an open circuit voltage (OCV) of 6.63 V with a good cycle performance. In particular, the ASSLBs present outstanding safety in terms of nail penetration and burning in fire. Therefore, this advanced cell construction strategy may generate tremendous opportunities in the search for novel emerging solid-state lithium metal batteries.

Study on the Li + Insertion/Extraction for Silicon Nanosized Silver Composite Electrode

Nanosized silver particle (<10 nm) was highly dispersed on the surface of silicon particle by electroless deposition on the basis of a stirred silver mirror reaction. Ex situ X-ray diffraction and discharge/charge cycling measurements indicated that silver, as well as silicon, participated in the insertion/extraction process of Li + and played a positive role in the complete extraction of Li + from silicon host. Furthermore, ordered structure of silicon can be obtained after the extraction of Li + with the help of silver additives, which indicates the effect of silver additives in promoting the recrystallization of amorphous Li + -extracted silicon.

Interface Re-Engineering of Li10GeP2S12 Electrolyte and Lithium anode for All-Solid-State Lithium Batteries with Ultralong Cycle Life

An ingenious interface re-engineering strategy was applied to in situ prepare a manipulated LiH2PO4 protective layer on the surface of Li anode for circumventing the intrinsic chemical stability issues of Li10GeP2S12 (LGPS) to Li metal, specifically the migration of mixed ionic-electronic reactants to the inner of LGPS, and the kinetically sluggish reactions in the interface. As consequence, the stability of LGPS with Li metal increased substantially and the cycling of symmetric Li/Li cell showed that the polarization voltage could keep relative stable for over 950 h at 0.1 mA cm-2 within ±0.05 V. The optimized ASSLiB of LiCoO2 (LCO)/LGPS/Li with interface-engineered structure was able to deliver long cycle life and high capacity, i.e., a reversible discharge capacity of 131.1 mAh g-1 at the initial cycle and 113.7 mAh g-1 at the 500th cycle under 0.1 C with a retention of 86.7%. In addition, the factors effected on the interphases formation of the LGPS/Li interface were analyzed, and the mechanism of the stability between LGPS and Li anode with protective layer was further investigated. Moreover, the probable causes of battery degradation were also explored. Above all, this work would give an alternative strategy for the modification of Li anode in high energy density solid-state lithium metal batteries.