Shiyou Li

Studies on Electrochemical Performances of Novel Electrolytes for Wide-Temperature-Range Lithium-Ion Batteries

Wide-temperature electrochemical behaviors of sulfolane (SL) with lithium difluoro(oxalato)borate (LiODFB) are studied using dimethyl sulfite (DMS) and diethyl sulfite (DES) as mixed solvents, respectively. In LiFePO4/Li cells, LiODFB-SL/DMS and LiODFB-SL/DES electrolytes always exert several advantages over a wide temperature range, such as stable cycling performance and good rate performance. Besides, in Li/mesophase carbon microbead cells, these novel electrolytes respectively exhibit excellent film-forming characteristics at both +60 and -20 °C, such as the formation of a stable and conductive SEI layer. It suggests that LiODFB-SL/DMS and LiODFB-SL/DES electrolytes are alterative candidate electrolytes for wide-temperature-range lithium-ion batteries.

Rubidium and Cesium Ion Adsorption by a Potassium Titanium Silicate-Calcium Alginate Composite Adsorbent

In this work, a composite spherical adsorbent, which employs potassium titanium silicate as an adsorption active component, and calcium alginate as a carrier, was successfully prepared. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the adsorbent. The kinetics and thermodynamics of rubidium and cesium ions adsorption were investigated comprehensively, by considering the effects of initial concentration, temperature, solution pH, and coexisting NaCl. According to the determination coefficients, the pseudo second-order kinetic model provided an impressive and comparable correlation, and the second-order rate constant and the initial adsorption rate increase with increasing temperature. In general, the equilibrium adsorption amount increases with the increasing initial metal ion concentration, but decreases with increasing coexisting NaCl. The adsorption capacity keeps constant in the pH value range 3-12 and slightly fades when the temperature increases from 25 to 55°C. Under similar conditions, rubidium and cesium show the similar adsorption amount. The adsorbent has a fast adsorption rate and an adsorption capacity of about 1.55 mmol g−1 for rubidium and 1.47 mmol g−1 for cesium when the initial metal ion concentration is 0.10 mol L−1. The composite adsorbent is effective for the adsorption of rubidium or cesium ions from simulated brines.

Lithium difluoro(sulfato)borate as a salt for the electrolyte of advanced lithium-ion batteries

Novel lithium difluoro(sulfato)borate (LiBF2SO4) was synthesized by the reaction between (C2H5)2O·BF3 and basic Li2SO4 in an aprotic solvent. Compared with conventional LiPF6-based electrolytes, the LiBF2SO4-based electrolyte exhibits good electrochemical stability, stable cycle performance, super rate performance and reduced impedance.

Mn3O4 nano-sized crystals: Rapid synthesis and extension to preparation of nanosized LiMn2O4 materials

AbstractWith a novel gas–liquid reaction, a facile and rapid method has been successfully developed for the synthesis of nano-sized Mn3O4 crystals. Coupled with complementary experiments, preparation mechanisms of Mn(II) and Mn(III)Mn(III)Mn(II) coordination complexes as well as nano-sized Mn3O4 crystals are studied. Besides, as the extension of synthesis of nano-sized Mn3O4 crystals, the intermediate ammonia alkaline solution containing Mn(III)Mn(III)Mn(II) coordination complexes, which tend to decompose into nano-sized Mn3O4 crystals spontaneously, are used to prepare nanosized LiMn2O4 materials. Although any physical treatment has been done to disperse powders, the as-synthesized LiMn2O4 nanoparticles are still existence with homogeneous size distribution (about 24.2 nm) without any obvious agglomeration. That is to say, the novel method is constructive not only to accelerate reaction rates for the elevated oxidation state of manganese ions, but also to prepare dispersed nanosized LiMn2O4 materials with good electrochemical properties. Graphical AbstractWith a novel gas–liquid reaction, a facile and rapid method has been successfully developed for the synthesis of nano-sized Mn3O4 crystals Besides, with intermediate ammonia alkaline solution containing Mn(III)Mn(III)Mn(II) coordination complexes, high-purity and wellcrystallized LiMn2O4 materials are obtained. The as-synthesized LiMn2O4 nanoparticles show good electrochemical properties..

Convenient synthesis and electrochemical performance investigation of nano-sized LiMn2O4

Nano-sized LiMn2O4 materials are synthesized via a simple one-step solid-state reaction using lithium acetate and lithium oxalate as lithium sources, respectively. The physical and electrochemical properties of LiMn2O4 materials are investigated by X-ray diffraction, scanning electron microscopy and electrochemical measurements. The results show that both of the as-prepared materials are pure nano-sized LiMn2O4 with narrow particle size distribution. Compared with lithium oxalate, lithium acetate is propitious to improve the crystallinity and size distribution of nano-sized LiMn2O4. Besides, LiMn2O4 synthesized from lithium acetate shows low resistance, good ability to inhibit Mn3+ dissolution, long cycle life and excellent rate property. Finally, the adverse effect of nano-sized LiMn2O4, which has increased contact area between acid-containing electrolyte and LiMn2O4 cathode electrode to aggravate dissolution and corrosion behavior, is treated by Li2CO3 additive in electrolyte. Results show that electrochemical performance of nano-sized LiMn2O4 is improved, due to the fact that Li2CO3 additive can not only consume HF and other Lewis acid in the commonly used LiPF6-based electrolyte, but also decrease interfacial impedance to promote the migration of Li+ ions through cathode surface film.

Oxidative stability and reduction decomposition mechanism studies on a novel salt: lithium difluoro(sulfato)borate

Lithium difluoro(sulfato)borate (LiBF2SO4) is a novel salt designed for battery electrolyte usage. Limited information is currently available, however, regarding its structure and chemical characteristics. The density functional theory calculation has therefore been used to explore both the oxidative stability and the reduction decomposition mechanism of LiBF2SO4. The results show that the oxidation potential (EOX) for LiBF2SO4 could be calculated using the correlation between the highest occupied molecular orbital energy and the corresponding EOX. In addition, the reduction decomposition mechanism of LiBF2SO4, particularly at a high potential of about 1.7 V (vs. Li/Li+) during the first discharge, has been calculated. In addition, many other electrolyte salts have also been investigated, to broaden the current knowledge of the use of chelato-borates as electrolyte components, to design and select high-performance electrolyte salts for lithium ion batteries, and to predict the chemical and physical characteristics of screening electrolyte salts, with the intent of using this induction for up-coming projected studies.

Enhanced elevated-temperature performance of Al-doped LiMn2O4 as cathodes for lithium ion batteries

Al-doped LiMn2O4 has been synthesized by a facile sol-gel method. The structure and morphology of the as-prepared products were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Galvanostatic charge/discharge tests indicate that the Al-doped LiMn2O4 delivers a discharge capacity of 120.1mA h g−1 at 0.5 C at room temperature, and about 93.3% of their initial capacity can be remained after 100 charge/discharge cycles with a current rate of 0.5 C at 50°C. Furthermore, Al-doped and high crystallinity can be well retained after 200 electrochemical cycles with a 0.5 C current rate at 25°C, revealing the excellent structure stability.Al-doped LiMn2O4 has been synthesized by a facile sol-gel method. The structure and morphology of the as-prepared products were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Galvanostatic charge/discharge tests indicate that the Al-doped LiMn2O4 delivers a discharge capacity of 120.1mA h g−1 at 0.5 C at room temperature, and about 93.3% of their initial capacity can be remained after 100 charge/discharge cycles with a current rate of 0.5 C at 50°C. Furthermore, Al-doped and high crystallinity can be well retained after 200 electrochemical cycles with a 0.5 C current rate at 25°C, revealing the excellent structure stability.

Electrochemical performance of LiNi0.5Mn1.5O4 doped with la and its compatiblity with new electrolyte system

Cathode materials LiNi0.5Mn1.5O4 and LiNi0.5 − x/2LaxMn1.5 − x/2O4 (x = 0.04, 0.1, 0.14) were successfully prepared by the sol-gel self-combustion reaction (SCR) method. The X-ray diffraction (XRD) patterns indicated that, a few of doping La ions did not change the structure of LiNi0.5Mn1.5O4 material. The scanning electronic microscopy (SEM) showed that the sample heated at 800°C for 12 h and then annealed at 600°C for 10 h exhibited excellent geometry appearance. A novel electrolyte system, 0.7 mol L−1 lithium bis(oxalate)borate (LiBOB)-propylene carbonate (PC)/dimethyl carbonate (DMC) (1: 1, v/v), was used in the cycle performance test of the cell. The results showed that the cell with this novel electrolyte system performed better than the one with traditional electrolyte system, 1.0 mol L−1 LiPF6-ethylene carbonate (EC)/DMC (1: 1, v/v). And the electrochemical properties tests showed that LiNi0.45La0.1Mn1.45O4/Li cell performed better than LiNi0.5Mn1.5O4/Li cell at cycle performance, median voltage, and efficiency.

Improved electrochemical properties of nickel rich LiNi0.6Co0.2Mn0.2O2 cathode materials by Al2O3 coating

Al2O3 has successfully coated on LiNi0.6Co0.2Mn0.2O2 cathode material by a facile coating method. The results of scanning electron microscopy and transmission electron microscope images show that Al2O3 were successfully attached onto the surface of LiNi0.6Co0.2Mn0.2O2 as expected. Charge–discharge tests show that the Al2O3 coating LiNi0.6Co0.2Mn0.2O2 exhibits excellent electrochemical performance with a high initial discharge capacity of 180.2 mAh g-1 at 0.1 C and a high capacity retention of 95.2% after 100 cycles at room temperature under 1C. The superior performance of surface-modified LiNi0.6Co0.2Mn0.2O2 attributed to the uniform Al2O3 coating layer is expected to directly reduce the contact between the active cathode particles and electrolyte. Simultaneously, the uniform Al2O3 coating layer also improves structure stability and suppresses generation of oxygen.Al2O3 has successfully coated on LiNi0.6Co0.2Mn0.2O2 cathode material by a facile coating method. The results of scanning electron microscopy and transmission electron microscope images show that Al2O3 were successfully attached onto the surface of LiNi0.6Co0.2Mn0.2O2 as expected. Charge–discharge tests show that the Al2O3 coating LiNi0.6Co0.2Mn0.2O2 exhibits excellent electrochemical performance with a high initial discharge capacity of 180.2 mAh g-1 at 0.1 C and a high capacity retention of 95.2% after 100 cycles at room temperature under 1C. The superior performance of surface-modified LiNi0.6Co0.2Mn0.2O2 attributed to the uniform Al2O3 coating layer is expected to directly reduce the contact between the active cathode particles and electrolyte. Simultaneously, the uniform Al2O3 coating layer also improves structure stability and suppresses generation of oxygen.

Synthesis of LiNi0.5Mn1.5O4 nano/microspheres with adjustable hollow structures for lithium-ion battery

High-voltage spinel LiNi0.5Mn1.5O4 nano/microspheres with adjustable hollow structures have been fabricated based on the Kirkendall effect. The main characteristic is that the wall thickness of the hollow structure as well as the cavity size of the hollow structure can be adjusted by the different ratio of mixed precipitation agents. Especially, the diagrammatic sketch for the formation process of various LiNi0.5Mn1.5O4 materials with adjustable hollow structures is discussed. Besides, the results of electrochemical performance test show that LiNi0.5Mn1.5O4 obtained from 10:1 Na2CO3/NaOH (in mole) ratio is worth looking forward to, owing to its special hierarchical nano/microsphere and moderate hollow structures.