High throughput production of nanocomposite SiOx powders by plasma spray physical vapor deposition for negative electrode of lithium ion batteries

Nanocomposite Si/SiO_x powders were produced by plasma spray physical vapor deposition (PS-PVD) at a material throughput of 480 g h⁻¹. The powders are fundamentally an aggregate of primary ∼20 nm particles, which are composed of a crystalline Si core and SiO_x shell structure. This is made possible by complete evaporation of raw SiO powders and subsequent rapid condensation of high temperature SiO_x vapors, followed by disproportionation reaction of nucleated SiO_x nanoparticles. When CH₄ was additionally introduced to the PS-PVD, the volume of the core Si increases while reducing potentially the SiO_x shell thickness as a result of the enhanced SiO reduction, although an unfavorable SiC phase emerges when the C/Si molar ratio is greater than 1. As a result of the increased amount of Si active material and reduced source for irreversible capacity, half-cell batteries made of PS-PVD powders with C/Si = 0.25 have exhibited improved initial efficiency and maintenance of capacity as high as 1000 mAh g⁻¹ after 100 cycles at the same time.     

Engineering the surface of LiCoO2 electrodes using atomic layer deposition for stable high-voltage lithium ion batteries

Developing advanced technologies to stabilize positive electrodes of lithium ion batteries under high-voltage operation is becoming increasingly important,owing to the potential to achieve substantially enhanced energy density for applications such as portable electronics and electrical vehicles.Here,we deposited chemically inert and ionically conductive LiAlO2 interfacial layers on LiCoO2 electrodes using the atomic layer deposition technique.During prolonged cycling at high-voltage,the LiAlO2 coating not only prevented interfacial reactions between the LiCoO2 electrode and electrolyte,as confirmed by electrochemical impedance spectroscopy and Raman characterizations,but also allowed lithium ions to freely diffuse into LiCoO2 without sacrificing the power density.As a result,a capacity value close to 200 mA·h·g-1 was achieved for the LiCoO2 electrodes with commercial level loading densities,cycled at the cut-off potential of 4.6 V vs.Li+/Li for 50 stable cycles;this represents a 40％ capacity gain,compared with the values obtained for commercial samples cycled at the cut-off potential of 4.2 V vs.Li+/Li.     

Electrodeposition of amorphous silicon anode for lithium ion batteries

Amorphous silicon has been successfully electrodeposited on copper using a SiCl₄ based organic electrolyte under galvanostatic conditions. The electrodeposited silicon films were characterized for their composition, morphology and structural characteristics using glancing angle X-ray diffraction (GAXRD), scanning electron microscopy (SEM), and Raman spectroscopy. GAXRD and Raman analyses clearly confirm the amorphous state of the deposited silicon film. The deposited films were tested for possible application as anodes for Li-ion battery. The results indicate that this binder free amorphous silicon anode exhibits a reversible capacity of ∼1300 mAh g⁻¹ with a columbic efficiency of >99.5% up to 100 cycles. Impedance measurements at the end of each charge cycle show a non-variable charge transfer resistance which contributes to the excellent cyclability over 100 cycles observed for the films. This approach of developing thin amorphous silicon films directly on copper eliminates the use of binders and conducting additives, rendering the process simple, facile and easily amenable for large scale manufacturing.     

Recent progress in electrode materials produced by spray pyrolysis for next-generation lithium ion batteries

We review the effect that various structures and composites synthesized by spray pyrolysis have on the electrochemical performance of next-generation electrodes for medium and large lithium ion batteries. The morphologies of electrode particles in particular have a strong influence on the capacity, power, safety, and cycle life. Recent progress in improving the electrochemical performance of electrodes is provided with a particular focus on electrodes composed of nanoparticles, core–shell or yolk–shell structures, and carbon-based composites. Finally, we propose a direction for future research for high-performance lithium ion batteries incorporating fabrication by spray pyrolysis.     

Closely packed Si@C and Sn@C nano-particles anchored by reduced graphene oxide sheet boosting anode performance of lithium ion batteries

Both silicon and tin are promising anodes for new generation lithium ion batteries due to high lithium storage capacities (theoretically 4200 mA h g-1 and 992 mA h g-1,respectively).However,their large volumetric expansions (both are above 300 ％) usually lead to poor cycling stability.In this case,we synthesized closely packed Si@C and Sn@C nano-particles anchored by reduced graphene oxide (denoted as Si@C/Sn@C/rGO) by the way of solution impregnation and subsequent hydrogenation reduction.Sn particles with a diameter of 100 nm are coated by carbon and surrounded by Si@C particles around 40 nm in average diameter through the high-resolution transmission electron microscopy.Expansions of Si and Sn are alleviated by carbon shells,and reduced graphene oxide sheets accommodate their volume changes.The prepared Si@C/Sn@C/rGO electrode delivers an enhanced initial coulombic efficiency (78％),rate capability and greatly improved cycle stability (a high reversible capacity of nearly 1000 mA h g-1 is achieved after 300 cycles at a current density of 1000 mA g-1).It can be believed that packing Sn@C nano-particles with Si@C relieves the volume expansion of both and releases the expansion stresses.Sn@C particles enhance anode process kinetics by reducing charge transfer resistance and increasing lithium ion diffusion coefficient.The present work provides a viable strategy for facilely synthesizing silicon-tin-carbon composite anode with long life.     

A controllable and byproduct-free synthesis method of carbon-coated silicon nanoparticles by induction thermal plasma for lithium ion battery

Carbon coated silicon nanoparticle is regarded as a promising anode material for the next generation of lithium ion batteries, while the development of a cost-effective and environmental-friendly preparation method is still difficult and hinders the practical implementation. In this research, a controllable and byproduct-free synthesis method is proposed for the preparation of silicon nanoparticles with amorphous hydrogenated carbon coating. The current apparatus is operated based on the application of induction thermal plasma. Plasma properties are tunable by adjusting the ratio of tangential and radial gas flow rates (T/R), which compose the plasma sheath gas. Obtained results reveal the plasma shape is shrunk with higher T/R values, which will lead to a steeper temperature gradient and lower temperature distributions in reaction chamber. Consequently, the compositions and properties of synthesized particles can be modified with T/R values. The formation of SiC, which was an intractable issue before, can be vanished at higher tangential gas flow rates in current research and the capacity of silicon anode for batteries will be improved in predict. This research is significant for a deep understanding of plasma synthesis processing and design of batteries with excellent performance.     

Enhancing the safety of lithium ion batteries by 4-isopropyl phenyl diphenyl phosphate

To enhance the safety of lithium ion batteries, 4-isopropyl phenyl diphenyl phosphate (IPPP) was explored as an additive in 1.0 M LiPF₆/ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 wt.%). The electrochemical performances of LiCoO₂/IPPP electrolyte/C cells were tested. And then the LiCoO₂/IPPP electrolyte/C cells were disassembled and wrapped to detect the thermal behaviors using a C80 microcalorimeter. The results indicated that 5% and 10% IPPP content in the electrolyte can enhance the safety of lithium ion batteries. Furthermore, the electrochemical performances of LiCoO₂/IPPP electrolyte/C cells become slightly worse by using 5% and 10% IPPP content electrolyte. Therefore, 5-10% IPPP content in electrolyte can enhance the safety of lithium ion batteries with minimum sacrifice in electrochemical performance.     

Evaluation of Si/Ge multi-layered negative film electrodes using magnetron sputtering for rechargeable lithium ion batteries

The capacity of a silicon anode diminishes during repeated lithium ion intercalation and extraction as the volume changes cause the active material to internally crack. In this study, electrodes are prepared by a deposition method, and silicon and germanium are deposited on the copper current collector in sequence. The number of layers is varied and we find evidence that a multi-layered structure is capable of improving cyclic ability. It is expected that germanium would act as a buffer against the volume change of the silicon and contribute to the elevating lithium ion diffusion. The morphologic changes and cyclic performances of the multi-layered electrodes prepared by the deposition method are observed. Deposited electrodes are verified by X-ray diffractometry, Raman spectroscopy, field-emission scanning electron microscopy and transmission electron microscopy. Si―Ge bonding at the interface is analyzed using extended X-ray absorption fine structure.     

Understanding of the capacity contribution of carbon in phosphorus-carbon composites for high-performance anodes in lithium ion batteries

Phosphorus has recently received extensive attention as a promising anode for lithium ion batteries (LIBs) due to its high theoretical capacity of 2,596 mAh·g-1.To develop high-performance phosphorus anodes for LIBs,carbon materials have been hybridized with phosphorus (P-C) to improve dispersion and conductivity.However,the specific capacity,rate capability,and cycling stability of P-C anodes are still less than satisfactory for practical applications.Furthermore,the exact effects of the carbon support on the electrochemical performance of the P-C anodes are not fully understood.Herein,a series of xP-yC anode materials for LIBs were prepared by a simple and efficient ball-milling method.6P-4C and 3P-7C were found to be optimum mass ratios of x/y,and delivered initial discharge capacities of 1,803.5 and 1,585.3.mAh.g-1,respectively,at 0.1 C in the voltage range 0.02-2 V,with an initial capacity retention of 68.3％ over 200 cycles (more than 4 months cycling life) and 40.8％ over 450 cycles.The excellent electrochemical performance of the 6P-4C and 3P-7C samples was attributed to a synergistic effect from both the adsorbed P and carbon.     

Electrochemical characterization of a Ge-based composite film fabricated as an anode material using magnetron sputtering for lithium ion batteries

Amorphous germanium and germanium-based films are sputter-deposited as anodes for lithium ion batteries. The structures of Ge and Ge-Mo composites are investigated using an X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The surface morphologies of the electrodes are observed using a field emission scanning electron microscope (FESEM). In order to determine the influence of inactive material in the anode, cell tests are carried out on half cells (Ge/Li metal and Ge_xMo_1 − x/Li metal) and full cells (Ge/LiCoO₂ and Ge_xMo_1 − x/LiCoO₂). The Ge film electrodes prepared on rough copper foil substrates showed stable capacities of 1000 mA h g⁻¹ over 50 cycles. The Ge_0.88Mo_0.12 composite film electrode showed reversible gravimetric capacities of up to 1000 mA h g⁻¹ with 77.9% capacity retention rates of the half-cell test after 100 cycles. Therefore, it may be possible to fabricate Ge-based anode materials with high capacity and improved capacity retention. The results of this study suggest that sputtered Ge-based electrodes are promising anode materials for next generation lithium ion batteries.     

Effects of annealing temperature on electrochemical performance of SnSx embedded in hierarchical porous carbon with N-carbon coating by in-situ structural phase transformation as anodes for lithium ion batteries

Tuned tin chalcogenides rooted in hierarchical porous carbon(HPC)with N-carbon coating layers are prepared by thermal shock under various temperatures(denoted as HPC-SnS2-PAN-Various T).With the increase of annealing temperature,the morphology and phase structure of SnS2,as well as the cyclization degree of polyacrylonitrile(PAN),are significantly changed,which leads to the formation of rod-like SnS and ordered structure of conductive N-carbon layer.By combining HPC,N-carbon coating derived from the cyclization of PAN,with 1D SnS nanorods generated from structural phase transformation of SnS2,the optimized composite(HPC-SnS2-PAN-500)as anode for lithium ion batteries(LIBs)provides buffer space for volume changes during alloying/dealloying process,builds a highly conductive network as well as decreases irreversible capacity from solid electrolyte interphase and enhances the ion/electron transport.Attributed to the above merits from composition regulation and architecture modification by sulfur depletion and PAN cyclization,this target anode exhibits an extraordinary cycling stability with a high specific capacity of 652.5 mA h/g at 0.5 A/g after 900 cycles.It suggests that rod-like SnS embedded in HPC with cyclized PAN layers by thermal treatment approach renders a potential structural design of anode materials for LIBs.     

Effect of impinging ion energy on the substrates during deposition of SiOx films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO_x films on bell metal substrates using Ar/hexamethyldisiloxane/O₂ glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO_x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si-O-Si chemical structure in the deposited SiO_x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO_x films is further confirmed from XPS analysis. The growth of SiO_x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO_x films for surface protection of bell metal is also explored.     

Characterization of TiO2 thin films prepared by electrolytic deposition for lithium ion battery anodes

The electrolytic deposition of TiO₂ thin films on platinum for lithium batteries is carried out in TiCl₄ alcoholic solution and the films are subsequently annealed. The as-prepared films are amorphous TiO(OH)₂·H₂O, transformed into anatase TiO₂ at 350 °C, and then gradually into rutile TiO₂ at 500 °C. Cyclic voltammograms show oxidation and reduction peaks at 2.20 and 1.61 V, respectively, corresponding to charge and discharge plateaus at 1.98 and 1.75 V vs. Li⁺/Li. The specific capacity decreases with increasing current density for film of 128-nm thickness in the initial discharge. It is observed that the diffusion flux of Li⁺ insertion/extraction into/from TiO₂ controls the reaction rate at higher current densities. Consequently, at low film thickness, high discharge capacity (per weight) is found for the initial cycle at a current density of 10 μA cm^− 2. However, the capacity of prepared films in various thicknesses approach 103 ± 5 mAh g^− 1 after 50 cycles, since the formation of cracks for thicker films offers shorter diffusion paths for Li⁺. In addition, TiO₂ films show electrochromic properties during lithiation and delithiation.     

High rate performance of novel cathode material Li1.33Ni1/3Co1/3Mn1/3O2 for lithium ion batteries

Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ with highly ordered structure has been successfully synthesized via a simple co-precipitation process. Charge–discharge tests showed that the initial discharge capacities are 153.0 mAh g⁻¹ and 128.9 mAh g⁻¹ at 5 C (1000 mA g⁻¹) and 10 C (2000 mA g⁻¹) between 2.5 and 4.5 V, respectively. The average full-charge time of this material is less than 12 min at 5 C and 6 min at 10 C. The electrode material composed of the prepared showed a better cyclability. The excellent high rate performance is attributed to the improved ordered layered structure and the electrical conductivity. The excess Li shorten Li⁺ diffusion distance between these submicron and nano-scaled particles. The results show that Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ cathode material has potential application in lithium ion batteries.     

锂离子电池正极材料LiNi0.5Mn1.5O4的固相法制备及性能研究

以Ni(CH3COO)2·4H2O和Mn(CH3COO)2·4H2O为原料,分别在400、500℃分解3、7h得到镍锰复合氧化物前驱体,再与锂源Li2CO3混匀,在800℃煅烧12h,600℃退火24h得到LiNi0.5Mn1.5O4正极材料。XRD、SEM、EIS和恒流充放电测试结果表明,在400℃、7h制备的前驱体与Li2CO3合成的LiNi0.5Mn1.5O4性能最佳。室温下以0.1C倍率充放电,首次放电比容量达到141.5mAh/g,循环30次后容量保持率为98.55%;以1C倍率充放电,首次放电比容量为120.34mAh/g,循环30次后放电比容量为112.09mAh/g。     

Impact of hydrogen dilution on optical properties of intrinsic hydrogenated amorphous silicon films prepared by high density plasma chemical vapor deposition for solar cell applications

P-i-n single-junction hydrogenated amorphous silicon (a-Si:H) thin film solar cells were successfully fabricated in this study on a glass substrate by high density plasma chemical vapor deposition (HDP-CVD) at low power of 50 W, low temperature of 200°C and various hydrogen dilution ratios (R). The open circuit voltage (V_oc ), short circuit current density (J_sc ), fill factor (FF) and conversion efficiency (η) of the solar cell as well as the refractive index (n) and absorption coefficient (α) of the i-layer at 600 nm wavelength rise with increasing R until an abrupt drop at high hydrogen dilution, i.e. R > 0.95. However, the optical energy bandgap (E_g ) of the i-layer decreases with the R increase. V_oc and α are inversely correlated with E_g . The hydrogen content affects the i-layer and p/i interface quality of the a-Si:H thin film solar cell with an optimal value of R = 0.95, which corresponds to solar cell conversion efficiency of 3.85%. The proposed a-Si:H thin film solar cell is expected to be improved in performance.     

Effects of double passivation for optimize DC properties in gamma-gate AlGaN/GaN high electron mobility transistor by plasma enhanced chemical vapor deposition

Two different materials for double passivation layers have been implemented to an AlGaN/GaN high electron mobility transistor on Si (111) substrate and the improved DC properties are demonstrated. Si₃N₄ and SiO₂ passivation materials are deposited on the gamma gate upper and bottom layers by plasma enhanced chemical vapor deposition. The gamma shape gate can be made by selectively accurate Si₃N₄ or SiO₂ first passivation dry etching with wet etching. The second passivation on gamma gate effectively increases the DC properties. The effects of DC properties of Si₃N₄ or SiO₂ single passivation and Si₃N₄/Si₃N₄ or SiO₂/SiO₂ double passivations are compared. The Si₃N₄/Si₃N₄ double passivation shows the maximum saturation current density and the peak extrinsic transconductance which increases up to 72% and 18%, respectively, more than Si₃N₄ single passivation and also up to 18% and 5% than SiO₂/SiO₂ double passivation.     

Structural, electrochemical and thermal properties of LiNi0.8−xCo0.2CexO2 as cathode materials for lithium ion batteries

A series of cathode materials for lithium ion batteries with the formula LiNi_0.8−xCo_0.2Ce_xO₂ (0 ≤ x ≤ 0.03) were synthesized by sol–gel method using citric acid as a chelating agent. The effects of cerium substitution on the structural, electrochemical and thermal properties of the cathode materials are investigated through X-ray diffraction (XRD), charge–discharge cycling, cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS) experiments and differential scanning calorimetry (DSC). Results show that the Ce substitution made the layered structure of materials more regular and less cation-ion mixing. An effective improved cycling performance is observed for cerium-doped cathode materials, which is interpreted to a significant suppression of phase transitions and charge-transfer impedance increasing during cycling. The thermal stability of cerium-doped materials is also improved, which can be attributed to its lower oxidation ability and enhanced structural stability at delithiated state.     

Electrochemical behaviors of Li[Li(1−x)/3Mn(2−x)/3Nix/3Cox/3]O2 cathode series (0 < x < 1) synthesized by sucrose combustion process for high capacity lithium ion batteries

A mixed cathode material between Li₂MnO₃ and Li[Mn_1/3Ni_1/3Co_1/3]O₂ for high capacity lithium secondary batteries was introduced in this study. It was prepared using the sucrose combustion process because this is a simple process. The oxidation states of Mn, Co and Ni ions in the pristine Li[Li_(1−x)/3Mn_(2−x)/3Ni_x/3Co_x/3]O₂ compounds were confirmed to be tetravalent, trivalent and divalent, respectively, via XANES measurements. Electrochemical charge/discharge studies showed that the highest first discharge capacity of 224 mAh/g was obtained in composition of x = 0.5 at a 0.2 C rate. The oxidation state of the Co and Ni ions in the Li[Li_1/6Mn_1/2Ni_1/6Co_1/6]O₂ changed to higher oxidation states, but that of the Mn ions did not change.