Xizheng Liu

Atomistic Origins of High Rate Capability and Capacity of N-Doped Graphene for Lithium Storage

Distinct from pure graphene, N-doped graphene (GN) has been found to possess high rate capability and capacity for lithium storage. However, there has still been a lack of direct experimental evidence and fundamental understanding of the storage mechanisms at the atomic scale, which may shed a new light on the reasons of the ultrafast lithium storage property and high capacity for GN. Here we report on the atomistic insights of the GN energy storage as revealed by in situ transmission electron microscopy (TEM). The lithiation process on edges and basal planes is directly visualized, the pyrrolic N hole defect and the perturbed solid-electrolyte-interface configurations are observed, and charge transfer states for three N-existing forms are also investigated. In situ high-resolution TEM experiments together with theoretical calculations provide a solid evidence that enlarged edge {0002} spacings and surface hole defects result in improved surface capacitive effects and thus high rate capability and the high capacity are owing to short-distance orderings at the edges during discharging and numerous surface defects; the phenomena cannot be understood previously by standard electron or X-ray diffraction analyses.

Amorphous Phosphorus/Nitrogen-Doped Graphene Paper for Ultrastable Sodium-Ion Batteries

As the most promising anode material for sodium-ion batteries (SIBs), elemental phosphorus (P) has recently gained a lot of interest due to its extraordinary theoretical capacity of 2596 mAh/g. The main drawback of a P anode is its low conductivity and rapid structural degradation caused by the enormous volume expansion (>490%) during cycling. Here, we redesigned the anode structure by using an innovative methodology to fabricate flexible paper made of nitrogen-doped graphene and amorphous phosphorus that effectively tackles this problem. The restructured anode exhibits an ultrastable cyclic performance and excellent rate capability (809 mAh/g at 1500 mA/g). The excellent structural integrity of the novel anode was further visualized during cycling by using in situ experiments inside a high-resolution transmission electron microscope (HRTEM), and the associated sodiation/desodiation mechanism was also thoroughly investigated. Finally, density functional theory (DFT) calculations confirmed that the N-doped graphene not only contributes to an increase in capacity for sodium storage but also is beneficial in regards to improved rate performance of the anode.

A quinone-based oligomeric lithium salt for superior Li–organic batteries

Organic electrode materials are promising alternatives to transition-metal based intercalation compounds for the next generation of high-performance and sustainable batteries. Herein, a novel quinone-based organic, lithium salt of poly(2,5-dihydroxy-p-benzoquinonyl sulfide) (Li2PDHBQS), was successfully synthesized through a simple one-step polycondensation reaction, and applied as a cathode for Li–organic batteries. As an oligomeric lithium salt with average polymerization degree of 7, Li2PDHBQS combines the advantages of the O⋯Li⋯O coordination bond and increased molecular weight, thus solves absolutely the dissolution problem of active material in non-aqueous electrolytes, which has seriously hindered development of organic electrode materials. Benefiting from the high theoretical capacity, intrinsic insolubility, fast reaction kinetics of the quinone group, accelerated Li-ion transport and uniform blending with conductive carbon, as well as the stable amorphous structure, Li2PDHBQS shows superior comprehensive electrochemical performance including high reversible capacity (268 mA h g−1), high cycling stability (1500 cycles, 90%), high rate capability (5000 mA g−1, 83%) and high Coulombic efficiency (99.9–100.1%). Investigation of the structure–property relationship of Li2PDHBQS and its analogues also gives new insights into developing novel quinone-based organic electrode materials, for building better Li–organic or Na–organic batteries beyond traditional Li-ion batteries.

Enhancing the performance of MnO by double carbon modification for advanced lithium-ion battery anodes

Porous hybrid materials with designed micro/nano-sub-structures have been recognized as promising anodes for lithium-ion batteries (LIBs) due to their high capacity and reliable performance. The low electrical conductivity and side-reactions at the interface of electrode/electrolyte prohibit their practical applications. Carbon material modification can effectively enhance the conductivity and mechanical properties, and suppress the direct contact between the electrode and electrolyte, leading to enhanced performance. Herein, unique porous MnO with micro/nano-architectures has been in situ decorated with carbon layers on the surface and by carbon nanotube doping between the particles (denoted as MnO@C/CNTs) by a catalytic chemical vapor deposition (CCVD) treatment. As anodes in LIBs, these MnO@C/CNTs exhibit remarkable cycling performance (1266 mA h g−1 after 300 cycles at 500 mA g−1) and good rate capability (850 mA h g−1 after 100 cycles at 100 mA g−1). The inspiring performance is associated with the carbon modified porous micro/nano-structure features which can buffer the volume expansion and promote the ion/electron transfer at the interface of electrode/electrolyte.

High stable post-spinel NaMn2O4 cathode of sodium ion battery

A spinel-type NaMn2O4 based on an inventive manganese and sodium compound has been synthesized under high pressure (4.5 GPa) for use as the cathode of a sodium ion battery. It exhibits a one-step voltage profile, limited polarization and good capacity retention both at room and high temperatures. The capacity retention is 94% after 200 cycles at room temperature. The stable battery performance is due to the high barrier of structure rearrangement and suppressed Jahn–Teller distortions in this post spinel structure.

In Situ Electrochemistry of Rechargeable Battery Materials: Status Report and Perspectives

The development of rechargeable batteries with high performance is considered to be a feasible way to satisfy the increasing needs of electric vehicles and portable devices. It is of vital importance to design electrodes with high electrochemical performance and to understand the nature of the electrode/electrolyte interfaces during battery operation, which allows a direct observation of the complicated chemical and physical processes within the electrodes and electrolyte, and thus provides real-time information for further design and optimization of the battery performance. Here, the recent progress in in situ techniques employed for the investigations of material structural evolutions is described, including characterization using neutrons, X-ray diffraction, and nuclear magnetic resonance. In situ techniques utilized for in-depth uncovering the electrode/electrolyte phase/interface change mechanisms are then highlighted, including transmission electron microscopy, atomic force microscopy, X-ray spectroscopy, and Raman spectroscopy. The real-time monitoring of lithium dendrite growth and in situ detection of gas evolution during charge/discharge processes are also discussed. Finally, the major challenges and opportunities of in situ characterization techniques are outlined toward new developments of rechargeable batteries, including innovation in the design of compatible in situ cells, applications of dynamic analysis, and in situ electrochemistry under multi-stimuli. A clear and in-depth understanding of in situ technique applications and the mechanisms of structural evolutions, surface/interface changes, and gas generations within rechargeable batteries is given here.

Crystalline Cu-silicide stabilizes the performance of a high capacity Si-based Li-ion battery anode

Metal-silicides have demonstrated bright prospects as advanced anodes for lithium-ion batteries (LIBs). However, their roles in volume change accommodations are still unclear to us. Here, we design and fabricate a nanoporous Si/Cu0.83Si0.17/Cu composite, supported with a highly crystalline Cu-silicide/Cu rigid framework, which demonstrates a high reversible capacity of 820.4 mA h g−1 after 500 cycles at a current density of 3 A g−1. According to the in situ TEM, there was no obvious structural damage and electrode pulverization during the initial lithiation, and a highly crystalline LiCuSi phase was observed. Furthermore, the conversion of the Cu0.83Si0.17/LiCuSi couple during repeated cycles is highly reversible, and the structural integrity could be well maintained. These results demonstrate that the highly crystalline Cu-silicide together with the nanoporous structure contributes to the ultrastable cycle performance and the Cu-silicide/Cu rigid framework supported the superior rate performance. The present work points out a facile but effective strategy for the engineering of alloy type anodes with superior cycle and rate properties for next generation LIBs.

Promotional recyclable Li-ion batteries by a magnetic binder with anti-vibration and non-fatigue performance

With the exponentially growing utilization of lithium ion batteries (LIBs), their manufacture and recycling technologies with low cost and low pollution emissions are drawing increasing attention. Herein, we proposed an intelligent battery architecture design with a Magnetic-Manipulated Electrode (MME) by exploiting magnetic Fe3O4 particles as binder. It greatly simplifies the LIB fabrication and recycling technologies, and decreases the total cost as well. In addition, a battery equipped with MME shows anti-vibration and non-fatigue performance.

Rechargeable Al–CO2 Batteries for Reversible Utilization of CO2

The excessive emission of CO2 and the energy crisis are two major issues facing humanity. Thus, the electrochemical reduction of CO2 and its utilization in metal-CO2 batteries have attracted wide attention because the batteries can simultaneously accelerate CO2 fixation/utilization and energy storage/release. Here, rechargeable Al-CO2 batteries are proposed and realized, which use chemically stable Al as the anode. The batteries display small discharge/charge voltage gaps down to 0.091 V and high energy efficiencies up to 87.7%, indicating an efficient battery performance. Their chemical reaction mechanism to produce the performance is revealed to be 4Al + 9CO2 ↔ 2Al2 (CO3 )3 + 3C, by which CO2 is reversibly utilized. These batteries are envisaged to effectively and safely serve as a potential CO2 fixation/utilization strategy with stable Al.

Enhanced anode performance of manganese oxides with petal-like microsphere structures by optimizing the sintering conditions

Herein, the rational design and synthesis of manganese oxides (MnO2 and MnO) have been achieved and both of them show petal-like microsphere structures. As anodes for LIBs, MnO exhibits a higher capacity of 751.4 mA h g−1 after 400 cycles (492.7 mA h g−1 for MnO2 after 300 cycles) at 2000 mA g−1.