Li Xinhai

Preparation and characteristics of Li2FeSiO4/C composite for cathode of lithium ion batteries

Abstract A Li2FeSiO4/C composite cathode for lithium ion batteries was synthesized at 650 °C by solid-state reaction. The effects of carbon sources and carbon content on the properties of the Li2FeSiO4/C composites were investigated. The crystalline structure, morphology, carbon content and charge/discharge performance of Li2FeSiO4/C composites were determined by X-ray diffraction(XRD), scanning electron microscopy(SEM), carbon/sulfur analyzer and electrochemical measurements. As carbon content increases in the range of 5%–20%, the amount of Fe3O4 impurity phase decreases. The SEM micrographs show that the addition of the carbon is favorable for reducing the Li2FeSiO4 grain size. Using sucrose as carbon source, the Li2FeSiO4/C composite with 14.5% carbon synthesized at 650 °C shows good electrochemical performance with an initial discharge capacity of 144.8 mA·h/g and a capacity retention ratio of 94.27% after 13 cycles.

Effect of activated carbon and electrolyte on properties of supercapacitor

Abstract Effect of activated carbon and electrolyte on electrochemical properties of organic supercapacitor was investigated. The results show that specific surface area and mesoporosity of activated carbon influence specific capacitance. If specific surface area is larger and mesoporosity is higher, the specific capacitance will become bigger. Specific surface area influences resistance of carbon electrode and consequently influences power property and pore size distribution. If specific surface area is smaller and mesoporosity is higher, the power property will become better. Ash influences leakage current and electrochemical cycling stability. If ash content is lower, the performance will become better. The properties of supercapacitor highly depend on the electrolyte. The compatibility of electrolyte and activated carbon is a determining factor of supercapacitors working voltage. LiPF 6 /(EC-EMC+DMC) is inappropriate for double layer capacitor. MeEt 3 NPF 4 /PC has higher specific capacitance than Et 4 NPF 4 /PC because methyls electronegativity value is lower than ethyl and MeEt 3 N + has more positive charges and stronger polarizability than Et 4 N + when an ethyl is substituted by methyl.

Extraction of lithium from lepidolite using chlorination roasting–water leaching process

Chlorination roasting followed by water leaching process was used to extract lithium from lepidolite. The microstructure of the lepidolite and roasted materials were characterized by X-ray diffraction (XRD). Various parameters including chlorination roasting temperature, time, type and amount of chlorinating agents were optimized. The conditional experiments indicate that the best mass ratio of lepidolite to NaCl to CaCl2 is 1:0.6:0.4 during the roasting process. The extraction of lithium reaches peak value of 92.86% at 880 °C, potassium, rubidium, and cesium 88.49%, 93.60% and 93.01%, respectively. The XRD result indicates that the major phases of the product after roasting lepidolite with mixture of chlorinating agents (CaCl2 and NaCl) are SiO2, CaF2, KCl, CaSiO3, CaAl2Si2O8, NaCl and NaAlSi3O8.

Nickel electrodeposition from novel citrate bath

Abstract A new type of electroplating bath suitable for nickel electrodeposition was developed. Trisodium citrate was used as a complexing agent and a buffer in the bath. The buffering capacity between trisodium citrate and boric acid were compared. The effects were investigated under different conditions of bath composition, current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency and throwing index, as well as the electrical conductivity of these baths. The optimum conditions for producing sound and satisfactory nickel deposits were: NiSO4-6H2O 350 g/L, NiCl2-6H2O 45 g/L and Na3C6H5O7 30 g/L at pH = 4 and 55 °C. The surface morphology of the as-plated Ni deposit was examined by SEM. The results reveal that the nickel deposition obtained from the optimum conditions are composed of compact, non-porous fine grains covering the entire surface. X-ray analysis shows that nickel deposits obtained from the citrate bath have a fine crystal structure compared with deposits from the Watts bath.

Diffusion coefficient of lithium in artificial graphite, mesocarbon microbeads, and disordered carbon

Abstract The structures of pyrolytic sugar carbon, resin carbon, artificial graphite and mesocarbon microbeads (MCMBs), and the diffusion coefficient of lithium in them were determined by X-ray diffraction and potential step chronoamperometry measurements. It was found that the diffusion coefficient of lithium was strongly dependent on the degree of discharge and the structure of the carbon an-odes. As the discharge degree increased, the diffusion coefficient of lithium in MCMB anodes decreased from 4.43×10-9 cm2/s to 5.24×10−10 cm2/s. At half discharge, the diffusion coefficients of lithium in sugar carbon, resin carbon, artificial graphite, and MCMB anode were 1.4×10−10 cm2/s, 5.75×10−10 cm2/s, 1.24×10−9 cm2/s, 2.1×10−9 cm2/s, respectively, showing that diffusion of lithium in soft carbons (artificial graphite and MCMBs) was much easier than that in hard carbons such as sugar and resin carbon.

Synthesis and electrochemical performance of 5V spinel LiNi0.5Mn1.5O4 prepared by solid-state reaction

Spinel compound LiNi0.5Mn1.5O4 with high capacity and high rate capability was synthesized by solid-state reaction. At first, MnCl2·4H2O and NiCl2·6H2O were reacted with (NH4)2C2O4·H2O to produce a precursor via a low-temperature solid-state route, then the precursor was reacted with Li2CO3 to synthesize LiNi0.5Mn1.5O4. The effects of calcination temperature and time on the physical properties and electrochemical performance of the products were investigated. Samples were characterized by thermal gravimetric analysis(TGA), scanning electron microscopy(SEM), X-ray diffractometry(XRD), charge-discharge tests and cyclic voltammetry measurements. Scanning electron microscopy(SEM) image shows that as calcination temperature and time increase, the crystallinity of the samples is improved, and their grain sizes are obviously increased. It is found that LiNi0.5Mn1.5O4 calcined at 800 °C for 6 h exhibits a typical cubic spinel structure with a space group of Fd3m. Electrochemical tests demonstrate that the sample obtained possesses high capacity and excellent rate capability. When being discharged at a rate as high as 5C after 30 cycles, the as-prepared LiNi0.5Mn1.5O4 powders can still deliver a capacity of 101 mA·h/g, which shows to be a potential cathode material for high power batteries.

Pretreatment study on chloridizing segregation and magnetic separation of low-grade nickel laterites

Abstract The chloridizing segregation and magnetic separation of low-grade nickel laterites from Yunnan province of China was investigated. The nickel laterites were characterized by microscopic investigations, using X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS) techniques. The pellets, which were prepared with magnesium chloride and coke as chloride agent and reductant respectively, were heated to a high temperature, and the pellets after cooling were crushed for magnetic separation. A series of experiments were conducted to examine the effect of chlorinating agent dosage, reductant dosage, chloridizing temperature and chloridizing time on enrichment grade of Ni and Co. The results indicate that the four factors have significant effects on the extractions of Ni and Co. The optimum conditions are as follows: the amounts of magnesium chloride and coke are 6% and 2%, respectively, chloridizing temperature is 1 253 K, and chloridizing time is 90 min. Under the conditions, extractions of Ni and Co reach 91.5% and 82.3%, respectively.

Study of spent battery material leaching process

The recovery of Ni, Co and Mn from spent battery material is very important to environment protection, utilization of resources and cost reduction of the material. The dissolution rates of Ni, Co and Mn with hydrochloric acid as leachant are all over 95% under the optimal conditions of initial hydrochloric acid of 6 mol/L, particle size of 120 μm for the exhausted scraps, molar ratio of H2O2 to MeS of 2, leaching temperature about 60 °C, ratio of liquid to solid of 8, and leaching time of 2 h. The NixCoyMnz precursor for cathode material prepared from the purified leaching solution, can meet the demand of precursor by pure chemicals. The process is economic and feasible for base metals from spent battery material.

Recycle and synthesis of LiCoO2 from incisors bound of Li-ion batteries

A new LiCoO2 recovery technology of Li-ion battery was studied. LiCoO2 was initially separated from the Al foil with dimethyl acetamide(DMAC), and then the polyvinylidene fluoride(PVDF) and carbon powders in the active material were elimiated by high temperature calcining. The content of the elements in the recovered powder was analyzed. The structure and morphology of the resulted samples were observed by XRD and SEM. Then the Li2CO3 was added in the recycled powder to adjust the Li/Co molar ratio to 1. The new LiCoO2 was synthesized by calcining at 850 °C for 12 h in air. The well-crystallized single phase LiCoO2 without Co3O4 phase was obtained. The recycle-synthesized LiCoO2 powders have good characteristics as a cathode active material in terms of charge-discharge capacity and cycling performance.

Effects of calcination temperature on properties of Li2SiO3 for precursor of Li2FeSiO4

Abstract Li 2 SiO 3 was synthesized by combination of sol-gel method and calcination at high temperature using Li 2 CO 3 , HNO 3 , Si(OC 2 H 5 ) 4 and C 2 H 5 OH as starting materials. The effects of calcination temperature and refluxing system on the composition and properties of lithium silicate were investigated. The samples were characterized by TGA/DTA, XRD, SEM and particle size analysis. Li 2 FeSiO 4 was prepared by the solid-state reaction between Li 2 SiO 3 and FeC 2 O 4 ·2H 2 O. The XRD patterns show that the use of refluxing system in the sol-gel preparation can decrease the Li 2 Si 2 O 5 and Li 4 SiO 4 impurities in the Li 2 SiO 3 sample. The calcination temperature plays an important role in the properties of the Li 2 SiO 3 samples. The sample calcined at 700 °C has high purity of 97% Li 2 SiO 3 and good morphology as precursor of Li 2 FeSiO 4 . It consists of primary particles with size of 1–3 μm, and the primary particle clusters form agglomerates with loose and porous appearance.