Size effect of Si particles on the electrochemical performances of Si/C composite anodes

A series of Si/C composites were fabricated based on pitch and Si powders with particle sizes of 30, 100, 500, and3000 nm. The size effects of the Si particles in the Si/C composites were investigated for lithium-ion battery anodes. The nanoscale Si and Si/C composites exhibited good capacity retentions. Scanning electron microscopy showed that exterior and interior cracks emerging owing to volume expansion as well as parasitic reactions with the electrolyte could well explain the performance failure.     

锂电池原位与非原位表征技术研究

锂电池的电化学性能与电子及离子在体相与界面的输运、反应、储存行为有关. 从原子尺度到宏观尺度,对电池材料在平衡态与非平衡态过程的电子结构、晶体结构、微观形貌、化学组成、物理性质的演化研究对于理解锂离子电池中各类构效关系至关重要,这需要综合多种原位与非原位表征技术. 目前,基础研究处于前沿的发达国家在这些方面取得了卓有成效的进展. 本文简介了中国科学院物理研究所近年来通过国内外合作,采用原位X射线衍射（in-situ XRD）、原位X射线吸收谱（in-situ XAS）、准原位/原位扫描电镜（quasi/in-situ SEM）、球差校正扫描透射电镜（HAADF/ABF-STEM）、扫描力曲线（Force-Curve）、中子衍射（Neutron Diffraction）、热重-差示扫描量热-质谱联用（TG-DSC-MS）、表面增强拉曼（SERS）等技术研究锂离子电池电极材料结构演化方面的进展,并对未来锂离子电池研究中先进表征技术的发展进行了简要的探讨.     

Gas treatment protection of metallic lithium anode

The effects of different coating layers on lithium metal anode formed by reacting with different controlled atmospheres(argon,CO_2–O_2(2:1),N_2,and CO_2–O_2–N_2(2:1:3))have been investigated.The obtained XRD,second ion mass spectroscopy(SIMS),and scanning probe microscope(SPM)results demonstrate the formation of coating layers composed of Li_2CO_3,Li_3N,and the mixture of them on lithium tablets,respectively.The Li/Li symmetrical cell and Li/S cell are assembled to prove the advantages of the protected lithium tablet on electrochemical performance.The comparison of SEM and SIMS characterizations before/after cycles clarifies that an SEI-like composition formed on the lithium tablets could modulate the interfacial stabilization between the lithium foil and the ether electrolyte.     

Influence of fluoroethylene carbonate on the solid electrolyte interphase of silicon anode for Li-ion batteries:A scanning force spectroscopy study

Silicon is an important high capacity anode material for the next generation Li-ion batteries.The electrochemical performances of the Si anode are influenced strongly by the properties of the solid electrolyte interphase(SEI).It is well known that the addition of flouroethylene carbonate(FEC)in the carbonate electrolyte is helpful to improve the cyclic performance of the Si anode.The possible origin is suggested to relate to the modification of the SEI.However,detailed information is still absent.In this work,the structural and mechanical properties of the SEI on Si thin film anode in the ethylene-carbonate-based(EC-based)and FEC-based electrolytes at different discharging and charging states have been investigated using a scanning atomic force microscopy force spectroscopy(AFMFS)method.Single-layered,double-layered,and multi-layered SEI structures with various Young’s moduli have been visualized three dimensionally at nanoscale based on the hundreds of force curves in certain scanned area.The coverage of the SEI can be obtained quantitatively from the two-dimensional(2D)project plots.The related analysis indicates that more soft SEI layers are covered on the Si anode,and this could explain the benefits of the FEC additive.     

纯相Li_2MnO_3薄膜的制备及作为锂离子电池正极材料的电化学行为

采用固相烧结法制备了纯相Li2MnO3正极材料及靶材,采用脉冲激光沉积(PLD)法在氧气气氛、不同温度下沉积了Li2MnO3薄膜.通过X射线衍射(XRD)和拉曼(Raman)光谱表征了薄膜的晶体结构,采用扫描电镜(SEM)观察薄膜形貌及厚度,利用电化学手段测试了Li2MnO3薄膜作为锂离子电池正极材料性能.结果表明,PLD方法制备的纯相Li2MnO3薄膜随着沉积温度升高薄膜结晶性变好.25℃沉积的薄膜难以可逆充放电,400℃沉积的薄膜具有较高的电化学活性和循环稳定性.相对于粉末材料,400与600℃制备的Li2MnO3薄膜电极平均放电电位随着循环次数的衰减速率明显低于相应的粉体材料.     

Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives

The <100> crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate (FEC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), and vinyl carbonate (VC) electrolyte additives in the LiPF₆ dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.     

纯相Li2MnO3薄膜的制备及作为锂离子电池正极材料的电化学行为

采用固相烧结法制备了纯相Li₂MnO₃正极材料及靶材,采用脉冲激光沉积（PLD）法在氧气气氛、不同温度下沉积了Li₂MnO₃薄膜. 通过X射线衍射（XRD）和拉曼（Raman）光谱表征了薄膜的晶体结构,采用扫描电镜（SEM）观察薄膜形貌及厚度,利用电化学手段测试了Li₂MnO₃薄膜作为锂离子电池正极材料性能. 结果表明,PLD 方法制备的纯相Li₂MnO₃薄膜随着沉积温度升高薄膜结晶性变好. 25 ℃沉积的薄膜难以可逆充放电,400 ℃沉积的薄膜具有较高的电化学活性和循环稳定性. 相对于粉末材料,400与600 ℃制备的Li₂MnO₃薄膜电极平均放电电位随着循环次数的衰减速率明显低于相应的粉体材料.     

A low cost composite quasi-solid electrolyte of LATP,TEGDME,and LiTFSI for rechargeable lithium batteries

The composite quasi solid state electrolytes(CQSE) is firstly synthesized with quasi solid state electrolytes(QSE) and lithium-ion-conducting material Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3(LATP), and the QSE consists of [LiG4][TFSI] with fumed silica nanoparticles. Compared with LATP, CQSE greatly improves the interface conductance of solid electrolytes. In addition,it has lower liquid volume relative to QSE. Although the liquid volume fraction of CQSE is droped to 60%, its conductivity can also reach 1.39 × 10~(-4)S/cm at 20℃. Linear sweep voltammetry(LSV) is conducted on each composite electrolyte.The results show the possibility that CQSE has superior electrochemical stability up to 5.0 V versus Li/Li+. TG curves also show that composite electrolytes have higher thermal stability. In addition, the performance of Li/QSE/Li Mn_2O_4 and Li/CQSE/Li Mn_2O_4 batteries is evaluated and shows good electrochemical characteristics at 60℃.     

Probing component contributions and internal polarization in silicon-graphite composite anode for lithium-ion batteries with an electrochemical-mechanical model

Silicon-graphite (Si-Gr) composite anodes are attractive alternatives to replace Gr anodes for lithium-ion batteries (LIBs) owing to their relatively high capacity and mild volume change. However, it is difficult to understand electrochemical interactions of Si and Gr in Si-Gr composite anodes and internal polarization of LIBs with regular experiment methods. Herein, we establish an electrochemical-mechanical coupled model to study the effect of rate and Si content on the electrochemical and stress behavior in a Si-Gr composite anode. The results show that the composites of Si and Gr not only improve the lithiation kinetics of Gr but also alleviate the voltage hysteresis of Si and decrease the risk of lithium plating in the negative electrode. What's more, the Si content is a tradeoff between electrode capacity and electrode volume variation. Further, various internal polarization contributions of cells using Si-Gr composite anodes are quantified by the voltage decomposition method. The results indicate that the electrochemical polarization of electrode materials and the electrolyte ohmic over-potential are dominant factors in the rate performance of cells, which provides theoretical guidance for improving the rate performance of LIBs using Si-Gr composite anodes.     

高容量金属镓薄膜和粉体作为锂离子电池负极材料的自修复行为研究

锂离子电池合金类负极材料比如Si, Sn, 因其理论容量远高于目前商业化石墨负极材料受到了广泛的关注. 然而, 受限于这类材料的循环稳定性, 距离其产业化仍然有一定的距离, 主要是由于其在电化学充放电过程中锂离子的嵌入和脱出产生巨大的应力而导致出现的不可修复的裂纹. 利用金属镓低熔点的物理特性, 在其熔点之上研究其脱嵌锂过程中的自修复能力. 对制备出金属镓薄膜电极研究发现, 25次充放电后, 因为固体电解质(SEI)的持续生成, 有效自修复区域降低为34 μm, 自修复区域随着循环次数的增加逐渐降低. 同时通过简单的液相分散方法制备出金属镓粉末电极, 金属镓粉末大小为3.43 μm, 尺寸小于有效自修复区域, 电化学分析显示该金属镓粉末电极前25次循环能够实现高的可逆容量和稳定的循环性能, 25次循环后的金属镓粉末电极的SEM分析显示裂纹平均尺寸大小为1 μm, 说明金属镓在液体电解液体系中的自修复能力有限. 金属镓有望用于非液态电解质体系中的裂纹修复, 比如对全固态电池中金属锂粉化的修复.