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Zhangjiagang, China

Zheng H.,Soochow University of China | Tan L.,Soochow University of China | Zhang L.,Soochow University of China | Qu Q.,Soochow University of China | And 3 more authors.
Electrochimica Acta | Year: 2015

Abstract Commercial 18650 LiFePO4 (LFP)/graphite cells were subject to deep charge-discharge cycling and constant voltage storage tests. The capacity decay of the cells under charge-discharge cycling was correlated with lithium deposition on the graphite surface. The results show that lithium inventory loss is the main cause for the capacity loss and the majority of active lithium loss can be found on the graphite surface due to the growth of the solid electrolyte interphase (SEI). When the cells were held at different voltages for 60 days, negligible capacity loss was obtained compared to that underwent deep charge-discharge cycling, implying that cell voltage is not an important factor affecting the SEI stability and lithium consumption. The damage and repair of SEI film mainly results from the volume change of graphite particle due to lithium insertion and extraction. © 2015 Published by Elsevier Ltd. Source

Zhang L.,Soochow University of China | Zhang J.,Soochow University of China | Xue P.,Soochow University of China | Hao W.,Soochow University of China | And 2 more authors.
Carbon | Year: 2015

In the past decade, there have been great advances in the controllable growth of two-dimensional (2D) graphene sheets. However, the preparation of 3D structured graphene such as graphene coatings on arbitrary-shaped micro/nano materials still remains a formidable challenge. Herein, we have proposed a general strategy for the in situ growth of 3D graphene coatings on the micro/nano particles with arbitrary shapes. Inspired by the CVD growth mechanism of 2D graphene sheets on the bulk metal substrates, we have in situ constructed a nanometer-thick catalytic interface on the micro/nano particle surface by introducing a trace amount of transition metal salts and solid carbon sources with strictly-controlled content and ratio. Growth of 3D graphene coatings is accomplished through a solid-state reaction. Under the catalysis of the in situ formed catalytic interface consisting of highly-ordered metal nanoislands, the nano-thick amorphous carbon layer which arousing from the pyrolysis of carbon sources can be effectively transformed into a continuous and uniform graphene coating throughout the material surface based on a "dissolution-precipitation" mechanism. 3D graphene coatings have been successfully grown on lithium iron phosphate, silver, copper and silicon particles. The growth mechanism of the 3D graphene coatings has been studied in detail and a growth model is also proposed. © 2015 Elsevier Ltd. All rights reserved. Source

Liu H.,Soochow University of China | Zhu G.,Soochow University of China | Zhang L.,Soochow University of China | Qu Q.,Soochow University of China | And 2 more authors.
Journal of Power Sources | Year: 2014

A spinel lithium nickel manganese oxide (LiNi0.5Mn1.5O4) cathode material is synthesized with a modified oxalate co-precipitation method by controlling pH value of the precursor solution and introducing excessive Li source in the precursor. All the samples synthesized through this method are of Fd3m phase with a small amount of P4332 phase. It is found that pH value of the precursor solution considerably affects the morphology, stoichiometry and crystallographic structure of the target material, thereby resulting in different amounts of Mn3+ (i.e., different degree of disorder). 5% excessive Li source in the precursor may compensate for the lithium loss during the high-temperature sintering process and eliminate the LixNi1-xO impurity phase. Under the optimized synthesis conditions, the obtained high-purity LiNi0.5Mn1.5O4 spinel exhibits enhanced electrochemical performances. A reversible capacity of ca. 140 mAh g-1 can be delivered at 0.1C and the electrode retains 106 mAh g-1 at 10C rate. When cycled at 0.2C, a capacity retention of more than 98% is obtained in the initial 50 electrochemical cycles. © 2014 Elsevier B.V. Source

Yun J.,Soochow University of China | Zhang L.,Soochow University of China | Qu Q.,Soochow University of China | Liu H.,Soochow University of China | And 3 more authors.
Electrochimica Acta | Year: 2015

To widen the operating potential window of electrolyte used for lithium-ion batteries, a binary cyclic carbonates-based electrolyte containing propylene carbonate (PC) and trifluoropropylene carbonate (TFPC) with an optimized volume ratio has been successfully proposed. The main function of additive TFPC is to establish a stable SEI layer on graphite electrode and suppress the intercalation reaction of PC molecules. Unlike the previous works, where the TFPC/PC involved electrolyte was simply estimated at a certain volume ration and recognized as an unfavorable system, in this work, the physical properties of the electrolyte solutions with a series of volume ratios of TFPC/PC and their electrochemical performances in a graphite/Li cell and 5 V LiNi0.5Mn1.5O4/Li cell have been systematically studied. The electrolyte of 1 mol dm-3 LiPF6-TFPC/PC (1:2) is adopted as the optimized system due to its high ionic conductivity, low viscosity, broad operating potential window, wide liquid temperature range (-50 ∼ 240 °C) and suitable film-forming property. Both the graphite and LiNi0.5Mn1.5O4 electrodes were found to exhibit high reversible capacity and superb rate performance in the optimized electrolyte, making us have a new recognition of this important binary solvent. Considering its excellent physical and electrochemical properties, we therefore anticipate that the electrolyte based on TFPC and PC is a possible candidate for future LIBs that can work in a broader temperature range and high operation potential conditions. © 2015 Elsevier Ltd. All rights reserved. Source

Zhang J.,Soochow University of China | Zhang L.,Soochow University of China | Xue P.,Soochow University of China | Zhang X.,Jiangsu Huasheng Corporation | And 4 more authors.
Journal of Materials Chemistry A | Year: 2015

A silicon-based anode material offers extremely high lithium storage capacity, but suffers from severe volume expansion during lithiation, which causes a drastic capacity decay. Embedding and isolating Si nanoparticles (SiNPs) into sealed amorphous carbon hollow spheres with sufficient voids is a promising strategy to accommodate the volume effect of Si. However, the created voids significantly compromise the volumetric energy density. Conversely, if insufficient voids are introduced, the inferior mechanical property of the amorphous carbon turns into the decisive factor destroying the structural integrity of the composites. Graphene is more suitable as a protective shell material due to its excellent mechanical strength. However, there still remains a formidable challenge of constructing closed graphene hollow spheres owing to their unique two-dimensional structure. Herein, we first propose a bottom-up route to controllably synthesize a polycrystalline graphene hollow sphere isolated SiNP nanocomposite (Si@void@graphene) through an in situ pyrolysis and metal-catalyzed graphitization reaction, in which glucose and metal sulfate with strictly controlled content and ratio are employed as the carbon source and catalyst precursor, respectively. The obtained graphene hollow spheres with superb mechanical properties offer a permanent structural and electrical environment for the inner SiNPs even insufficient voids are introduced while maintaining a reasonable volumetric energy density. When the void space is designed based on the assumption that Si has only 250% volume change, the Si@void@graphene electrode exhibits high reversible capacity, superior rate capability and much prolonged cycle life as compared to those of the Si@void@amorphous carbon electrode. © The Royal Society of Chemistry 2015. Source

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