Synthesis and electrochemical performance of La_(2)CuO_(4)as a promising coating material for high voltage Li-rich layered oxide cathodes

The structural transformations,oxygen releasing and side reactions with electrolytes on the surface are considered as the main causes of the performance degradation of Li-rich layered oxides(LROs)cathodes in Li-ion batteries.Thus,stabilizing the surfaces of LROs is the key to realize their practical application in high energy density Li-ion batteries.Surface coating is regarded as one of the most effective strategies for high voltage cathodes.The ideal coating materials should prevent cathodes from electrolyte corrosion and possess both electronic and Li-ionic conductivities simultaneously.However,commonly reported coating materials are unable to balance these functions well.Herein,a new type of coating material,La_(2)CuO_(4)was introduced to mitigate the surface issues of LROs for the first time,due to its superb electronic conductivity(26-35 mS·cm^(-1))and lithium-ionic diffusion coefficient(10^(-12)-10^(-13)cm^(2)·s^(-1)).After coating with the La_(2)CuO_(4),the capacity retention of Li_(1.2)Ni_(0.54)Co_(0.13)Mn_(0.13)O_(2)cathode was increased to 85.9%(compared to 79.3%of uncoated cathode)after 150 cycles in the voltage range of 2.0-4.8 V.In addition,only negligible degradations on the deliverable capacity and rate capability were observed.

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 LiPF_6 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.

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, and 3000 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.

Influence of carbon coating on the electrochemical performance of SiO@C/graphite composite anode materials

Silicon monoxide(SiO) has been considered as one of the most promising anode materials for next generation highenergy-density Li-ion batteries(LiBs) thanks to its high theoretical capacity. However, the poor intrinsic electronic conductivity and large volume change during lithium intercalation/de-intercalation restrict its practical applications. Fabrication of SiO/C composites is an effective way to overcome these problems. Herein, a series of micro-sized SiO@C/graphite(Si0@C/G) composite anode materials, with designed capacity of 600 mAh·g-1, are successfully prepared through a pitch pyrolysis reaction method. The electrochemical performance of SiO@C/G composite anodes with different carbon coating contents of 5 wt%, 10 wt%, 15 wt%, and 35 wt% is investigated. The results show that the SiO@C/G composite with15-wt% carbon coating content exhibits the best cycle performance, with a high capacity retention of 90.7% at 25℃ and90.1% at 45 0 C after 100 cycles in full cells with LiNi0.5Co0.2Mn0.3O2 as cathodes. The scanning electron microscope(SEM) and electrochemistry impedance spectroscopy(EIS) results suggest that a moderate carbon coating layer can promote the formation of stable SEI film, which is favorable for maintaining good interfacial conductivity and thus enhancing the cycling stability of SiO electrode.

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.

An Integrated Control Strategy Adopting Droop Control with Virtual Inductance in Microgrid

As there exists sorts of distributed generators in microgrid, an integrated control strategy containing different control methods against corresponding generators should be applied. The strategy in this paper involves PQ control and droop control methods. The former aims at letting generators like PV output maximum power. The latter stems from inverter parallel technique and applies to controlling generators which can keep the network voltage steady to make the parallel system reach the minimum circulation point. Due to the unworthiness of droop control applied in low-voltage microgrid of which the impedance ratio is rather high, the paper adopts the droop control introducing virtual generator and virtual impedance. Based on theoretical analysis, simulation in Matlab is also implemented to verify the feasibility of the strategy.

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.

Improvement of Cyclic Stability of Na_(0.67)Mn_(0.8)Ni_(0.1)Co_(0.1)O_(2 )via Suppressing Lattice Variation

Strategies to prolong operational life are highly pursued to strengthen the advantage of cost-effectiveness on sodium-ion batteries(SIBs).We demonstrate the crucial influence of particles'internal mechanical strains on durability of cathode,which does not attract enough attentions from the community.Among the investigated samples,2%Ti-modified-Na_(0.67)Ni_(0.1)Co_(0.1)Mn_(0.8)O_(2 )suppresses the c-axis lattice variation by 38%,attains the reversible capacity 86%higher after 200 cycles,and still keeps intact morphology.This approach indicates that the mechanical properties could tailor cyclic stability of cathode,which is particular important to further improve competitiveness for SIBs.

Wide-temperature range and high safety electrolytes for highvoltage Li-metal batteries

Along with the keeping growing demand for high-energy-density energy storage system,high-voltage Li-metal batteries(LMBs)have attracted many attentions.In view of many defects of the commercial electrolytes,such as flammability,limited operation temperature range,and severe Li dendrite growth,non-flammable phosphate-based localized highly concentrated electrolytes(LHCE)have been explored as one of the safe electrolytes for LMBs.But until now there is rare report on wide-temperature range LMBs using phosphate-based electrolytes.Here,we prepare a wide-temperature LHCE,which is composed of lithium difluoro(oxalato)borate(LiDFOB),triethyl phosphate(TEP),and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(HFE),and explore the applicability in wide-temperature LMBs from−40 to 70℃.In the LHCE,both TEP and HFE are non-flammable,and Li^(+) is highly coordinated with TEP and DFOB^(−),which can effectively inhibit the TEP decomposition on anode,and facilitate the preferential reduction of DFOB^(−),thus obtain a robust solid electrolyte interphase(SEI)to suppress Li dendrite growth and side reactions.Therefore,this LHCE can not only endow Li/Cu and Li/Li cells with high Coulombic efficiency(CE)and long cycling lifespan,but also be applied to LiFePO_(4)(LFP)/Li and LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)(NCM523)/Li LMBs.Most importantly,the NCM523/Li LMBs with LHCE can deliver stable cycling performance at 4.5 V high-voltage and high-temperature(70℃),as well as excellent low-temperature capacity retention even though both charging and discharging process were carried out at−40℃.