Recovery of valuable metals from lepidolite by atmosphere leaching and kinetics on dissolution of lithium

The lepidolite located in Yichun, Jiangxi Province, China, was adopted to investigate the recovery of alkali metals and leaching kinetics of lithium with sulphuric acid solution under atmospheric pressure. The results show that the recoveries of alkali metals were achieved under the leaching conditions: mass ratio of lepidolite with particle size less than 180 μm to sulphuric acid 1.2, leaching temperature 411 K, liquid-solid ratio 2.5∶1, and leaching time 10 h. Under the selected conditions for leaching experiment, the leaching rates of lithium, potassium, rubidium and caesium are 94.18%, 93.70%, 91.81% and 89.22%, respectively. The X-ray diffraction analysis for leaching residue indicates that no insoluble product forms during leaching. The chemical compositions of leaching residue reveal that trace iron, manganese and calcium disappear after acid leaching. The kinetics of leaching process for lithium follows shrinking core model of mixed control and the apparent activation energy is 17.21 kJ/mol. The reaction orders with respect to sulphuric acid concentration and liquid-solid ratio are determined to be 2.85 and 1.66, respectively. A semi-empirical rate equation was obtained to describe the leaching process. The kinetic analysis shows that the leaching process is controlled by diffusion through the insoluble layer of the associated minerals.

Review of silicon-based alloys for lithium-ion battery anodes

Silicon(Si)is widely considered to be the most attractive candidate anode material for use in next-generation high-energy-density lithium(Li)-ion batteries(LIBs)because it has a high theoretical gravimetric Li storage capacity,relatively low lithiation voltage,and abundant resources.Consequently,massive efforts have been exerted to improve its electrochemical performance.While some progress in this field has been achieved,a number of severe challenges,such as the element’s large volume change during cycling,low intrinsic electronic conductivity,and poor rate capacity,have yet to be solved.Methods to solve these problems have been attempted via the development of nanosized Si materials.Unfortunately,reviews summarizing the work on Si-based alloys are scarce.Herein,the recent progress related to Si-based alloy anode materials is reviewed.The problems associated with Si anodes and the corresponding strategies used to address these problems are first described.Then,the available Si-based alloys are divided into Si/Li-active and inactive systems,and the characteristics of these systems are discussed.Other special systems are also introduced.Finally,perspectives and future outlooks are provided to enable the wider application of Si-alloy anodes to commercial LIBs.

Mechanism for capacity fading of 18650 cylindrical lithium ion batteries

The mechanism for capacity fading of18650lithium ion full cells under room-temperature(RT)is discussedsystematically.The capacity loss of18650cells is about12.91%after500cycles.The cells after cycles are analyzed by XRD,SEM,EIS and CV.Impedance measurement shows an overall increase in the cell resistance upon cycling.Moreover,it also presents anincreased charge-transfer resistance(Rct)for the cell cycled at RT.CV test shows that the reversibility of lithium ioninsertion/extraction reaction is reduced.The capacity fading for the cells cycled can be explained by taking into account the repeatedfilm formation over the surface of anode and the side reactions.The products of side reactions deposited on separator are able toreduce the porosity of separator.As a result,the migration resistance of lithium ion between the cathode and anode would beincreased,leading the fading of capacity and potential.

Enhanced cycling stability of La modified LiNi_(0.8-x)Co_(0.1)Mn_(0.1)La_xO_2 for Li-ion battery

A series of layered LiNi0.8?xCo0.1Mn0.1LaxO2(x=0,0.01,0.03)cathode materials were synthesized by combining co-precipitation and high temperature solid state reaction to investigate the effect of La-doping on LiNi0.8Co0.1Mn0.1O2.A new phase La2Li0.5Co0.5O4was observed by XRD,and the content of the new phase could be determined by Retiveld refinement and calculation.The cycle stability of the material is obviously increased from74.3%to95.2%after La-doping,while the initial capacity exhibits a decline trend from202mA·h/g to192mA·h/g.The enhanced cycle stability comes from both of the decrease of impurity and the protection of newly formed La2Li0.5Co0.5O4,which prevents the electrolytic corrosion to the active material.The CV measurement confirms that La-doped material exhibits better reversibility compared with the pristine material.

Empirical decay relationship between ionic conductivity and porosity of garnet type inorganic solid-state electrolytes

Ionic conductivity is one of the crucial parameters for inorganic solid-state electrolytes.To explore the relationship between porosity and ionic conductivity,a series of Li_(6.4)Ga_(0.2)La_(3)Zr_(2)O_(12) garnet type solid-state electrolytes with different porosities were prepared via solid-state reaction.Based on the quantified data,an empirical decay relationship was summarized and discussed by means of mathematical model and dimensional analysis method.It suggests that open porosity causes ionic conductivity to decrease exponentially.The pre-exponential factor obeys the Arrhenius Law quite well with the activation energy of 0.23 eV,and the decay constant is averaged to be 2.62%.While the closed porosity causes ionic conductivity to decrease linearly.The slope and intercept of this linear pattern also obey the Arrhenius Law and the activation energies are 0.24 and 0.27 eV,respectively.Moreover,the total porosity is linearly dependent on the open porosity,and different sintering conditions will lead to different linear patterns with different slopes and intercepts.

纳米YSZ热障涂层高温时效过程中组织演变研究

燃气轮机长期运行过程中,热端部件如燃烧室内壁和前级涡轮叶片长期经受高温火焰冲击,涂层材料会产生时效行为。在时效过程中,热障涂层会发生组织演变,影响涂层性能与寿命。本文对一种高纯纳米YSZ热障涂层进行了不同温度的时效考核,研究材料在高温中组织演变行为,并对涂层孔隙率变化规律进行了热动力学分析。结果表明,在高温过程中,YSZ涂层中残留的纳米界面会进一步融合并逐渐演变为微米晶;受热动力学机制支配,涂层中孔隙闭合消损,造成涂层孔隙率下降。另外,本文还统计分析了涂层的相变行为。

Property and Oxidation Behaviours of (Mo,Cr)Si2 + ZrO2 Composite Produced by Pressure-Less Sintering

A composites of (Mo0.9Cr0.1)Si2 + 15vol% ZrO2 was prepared with powder metallurgy and Pressure- Less Sintering (PLS) method, aiming at applications of high temperature structural materials. Mechanical properties of the composites were assessed with hardness, indentation fracture toughness Kc and KIC tested using SEVNB, flexure strength at room temperature and 1200?C, and isothermal oxidation at 1400?C. The results showed that the native silica oxide and molybdenum-oxides on the silicide feedstock surface were significantly reduced in terms of Cr-alloying. (Mo0.9Cr0.1)Si2 and its composite also exhibited improved sinterability and grain growth, owing to the presence of (Cr, Mo)5Si3 at grain boundaries. Fracture toughness of the composite was increased by a factor of 1.6 to that in the monolithic silicide. Mechanical property of the composite at high temperature was not affected by Cr addition. However, the high temperature oxidation resistance was greatly improved in the (Mo0.9Cr0.1)Si2 + 15vol% ZrO2 compared with the non Cr-alloyed counterpart. The Cr-alloying effects on the microstructure, fracture behaviour, and high temperature oxidation resistance were discussed.

Effect of SnO_2 intermediate layer on performance of Ti/SnO_2/MnO_2 electrode during electrolytic-manganese process

SnO2intermediate layers were coated on the titanium(Ti)substrate by thermal decomposition.Scanning electronmicroscope(SEM)and X-ray diffraction(XRD)results show that uniform SnO2intermediate layers with rutile crystal structure weresuccessfully achieved.According to the results of linear sweep voltammetry(LSV),oxygen evolution potential(OEP)of theTi/SnO2/MnO2electrodes decreases with increasing SnO2content,indicating that the electro-catalytic oxidation activity of theelectrode increases.Accelerated service life tests results demonstrate that SnO2intermediate layer can improve the service life of theTi/SnO2/MnO2electrode.As the content of SnO2intermediate layer increases,the cell voltage and the energy consumption decreaseapparently.

Ultrathin porous graphitic carbon nanosheets activated by alkali metal salts for high power density lithium-ion capacitors

Graphitic carbons with reasonable pore volume and appropriate graphitization degree can provide efficient Li+/electrolyte-transfer channels and ameliorate the sluggish dynamic behavior of battery-type carbon negative electrode in lithium-ion capacitors(LICs).In this work,onion-like graphitic carbon materials are obtained by using carbon quantum dots as precursors after sintering,and the effects of alkali metal salts on the structure,morphology and performance of the samples are focused.The results show that alkali metal salts as activator can etch graphitic carbons,and the specific surface area and pore size distribution are intimately related to the description of the alkali metal salt.Moreover,it also affects the graphitization degree of the materials.The porous graphitic carbons(SGCs)obtained by NaCl activation exhibit high specific surface area(77.14 m^(2)·g^(-1))and appropriate graphitization degree.It is expectable that the electrochemical performance for lithium-ions storage can be largely promoted by the smart combination of catalytic graphitization and pores-creating strategy.High-performance LICs(S-GCs//AC LICs)are achieved with high energy density of 92 Wh·kg^(-1)and superior rate capability(66.3 Wh·kg^(-1)at10 A·g^(-1))together with the power density as high as10020.2 W·kg^(-1).