Haiping Liu

Gold Immersion Deposition on Electroless Nickel Substrates Deposition Process and Influence Factor Analysis

An immersion gold-plating process on electroless nickel substrate was investigated. The effects of gold salt, trisodium citrate, bath temperature, and pH on the gold-immersion-deposition process are also discussed. The study was performed by measuring the mixed potential-time curves in situ and electrochemical impedance spectroscopy in combination with X-ray fluorescence spectrometry (XRF) and atomic force microscopy (AFM) surface analysis. Electrochemical measurements and XRF results show that both the deposition rate and the mixed potential changed during the gold-deposition process. These variations reflect the change of electrode surface state. AFM analysis shows that the morphology of nickel surface changed greatly at the initial stage of gold deposition. A model for understanding the gold-immersion-deposition process was proposed based on the experimental data. The effects of KAu(CN) 2 , trisodium citrate, pH, and temperature on gold-immersion deposition are significant, via affecting the gold film formation and the deposition rate. The optimal conditions of aqueous solution for the gold-immersion plating were determined. The experimental results support the explanation of the proposed model.

Effect of 3-S isothiuronium propyl sulfonate on electroless nickel deposition

The effects of organic additive, 3-S isothiuronium propyl sulfonate (UPS) on bath stability, deposition rate, reaction activation energy, and Ni-P coating composition in acidic electroless nickel (EN) plating were investigated. The study was performed by measuring the polarization curves and X-ray fluorescence spectrometer (XRF) in combination with X-ray photoelectron spectroscopy (XPS) analysis. The results show that UPS improves bath stability and increases the reaction activation energy. At lower concentration, UPS is an effective accelerator for EN deposition; whereas, at higher concentration, it decreases deposition rate. It also reveals that UPS inhibits the anodic oxidation of hypophosphite and accelerates the cathodic reduction. In addition, UPS decreases the phosphorus content in Ni-P deposit and can be adsorbed on the deposit surface and compound with Ni2+. On the basis of these results, the effect mechanism of UPS on electroless nickel deposition was deduced.

Synthesis and electrochemical performance of Sn-doped LiNi0.5Mn1.5O4 cathode material for high-voltage lithium-ion batteries

LiNi0.5Mn1.5−xSnxO4 (0 ≤ x ≤ 0.1) cathode materials with uniform and fine particle sizes were successfully synthesized by a two-step calcination of solid-state reaction method. As the cathode materials for lithium ion batteries, the LiNi0.5Mn1.48Sn0.02O4 shows the highest specific capacity and cycle stability. In the potential range of 3.5–4.9 V at room temperature, LiNi0.5Mn1.48Sn0.02O4 composite material shows a discharge capacity of more than 117 mA h g−1 at 0.1 C, while the corresponding discharge capacity of undoped LiNi0.5Mn1.5O4 is only 101 mA h g−1. Moreover, in cycle performance, all the LiNi0.5Mn1.5−xSnxO4 (0 ≤ x ≤ 0.1) samples show better capacity retention than the undoped LiNi0.5Mn1.5O4 at 1 C rate after 100 cycles. Especially, for the LiNi0.5Mn1.5O4, the discharge capacity after 100 cycles is 90 mA h g−1, while the corresponding discharge capacities of the undoped LiNi0.5Mn1.5O4 is only 56.1 mA h g−1. The significantly enhanced DLi+ and the enlarged electronic conductivity make the Sn-doped spinel LiNi0.5Mn1.5O4 material present even more excellent electrochemical performances. These results reveal that Sn-doping is an effective way to improve electrochemical performances of LiNi0.5Mn1.5O4.摘要本文采用两步烧结高温固相法成功制备了锡掺杂LiNi0.5Mn1.5−xSnxO4 (0 ≤ x ≤ 0.1)锂离子电池正极材料. x为0.02时, LiNi0.5Mn1.48Sn0.02O4的比容量和循环性能最好. 室温下, 在3.5–4.9 V电压范围内, 0.1 C放电倍率, LiNi0.5Mn1.48Sn0.02O4的首次放电比容量为117 mA h g−1, 而没有锡掺杂的LiNi0.5Mn1.5O4只有101 mA h g−1. 此外, 1 C放电100个循环后, 所有锡掺杂后的LiNi0.5Mn1.5O4材料均保持了较高的放电比容量; 尤其是LiNi0.5Mn1.48Sn0.02O4, 100个循环后, 放电比容量为90 mA h g−1, 而纯的LiNi0.5Mn1.5O4, 100个循环后其放电比容量仅为56.1 mA h g−1. 锡掺杂后的LiNi0.5Mn1.48Sn0.02O4材料具有比LiNi0.5Mn1.5O4材料及其他组材料更高的锂离子扩散效率, Sn离子的掺杂有利于锂离子的扩散和导电性的提高, 从而提高了LiNi0.5Mn1.5O4的电化学性能. 因此锡掺杂是一种有效的改善高电压锂离子电池材料LiNi0.5Mn1.5O4电化学性能的方法.

Effects of organic additives on the immersion gold depositing from a sulfite–thiosulfate solution in an electroless nickel immersion gold process

An immersion gold-plating process on electroless Ni–P alloy substrate was investigated. The immersion Au coating was deposited from a thiosulfate–sulfite mixed ligand bath based on Ni–P alloy substrate. The effects of three organic additives, such as polyethylenimine (PEI), hexamethylene tetramine (HET) and benzotriazole (BTA) on the depositing process and the performance of Au coating were investigated. The study was performed by measuring the open circuit potential–time curves in situ and Tafel tests in combination with X-ray fluorescence spectrometry (XRF), scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) analysis techniques. The results show that PEI, HET and BTA could adsorb and desorb on the surface of Au coating and they had the similar influences on the open circuit potential. With these organic compounds adding, the plateau potential shifts to the positive direction, and the time for the potential to reach the plateau value decreases with increasing additive concentration. The XRF, XRD and SEM studies indicated that these three additives decreased the initial deposition rate, decreased the size of Au particles, and thus changed the morphology of Au deposits. Tafel studies demonstrated that the corrosion resistance of Au coating could be improved by adding PEI, HET or BTA to immersion gold bath. A cause for understanding these additives was indicated based on the above experiments.

Enhanced rate performance of nanosized RGO-LiNi 0.5 Mn 1.5 O 4 composites as cathode material by a solid-state assembly method

In this paper, LiNi0.5Mn1.5O4 (LNMO) coated with various amount of RGO (0, 0.5, 1, and 2xa0wt%) were successfully synthesized by solid-state assembly method. The physical properties of LNMO and RGO-LNMO were investigated by x-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), and transmission electron microscope (TEM). XRD and Raman spectrum exhibit all samples that are well crystallized in P4332 space group; SEM and TEM results show the uniform size of the particles is 1u2009~u20092xa0μm with octahedral structure, and LNMO is successfully wrapped by RGO. The electrochemical properties of RGO-LNMO visibly improved compared with the bared LNMO, especially at high current rate, which has been proven by galvanostatic charge-discharge test, cycle performance test, and rate capacity test. For example, the bared LNMO delivers a discharge capacity of 39.2xa0mAhxa0g−1 at 10xa0C rate, while that of 1-wt% RGO-LNMO was 86.2xa0mAhxa0g−1, which was approximately 2.5 times more than that of the bared LNMO. At 10xa0C rate after 1000xa0cycles, 2-wt% RGO-LNMO delivers a discharge capacity of 50.6xa0mAhxa0g−1 with a capacity retention of 86.7%, while the bared LNMO delivers a discharge capacity of 27.6xa0mAhxa0g−1 with a capacity retention of 52.5%, only about 54% of the 2-wt% RGO-LNMO. EIS results show the charge transfer resistance of LNMO decreased after coating with RGO, which was favorable for improving electrochemical performance.

Synthesis and characterization of high-performance RGO-modified LiNi0.5Mn1.5O4 nanorods as a high power density cathode material for Li-ion batteries

Micronanosized LiNi0.5Mn1.5O4 nanorods coated with reduced graphene oxide is successfully synthesized by a hydrothermal-assembly method. The as-prepared samples are characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscope, and electrochemical tests. The XRD and Raman results show that the LiNi0.5Mn1.5O4 nanorods have disordered structure of Fd-3m space group. The SEM characterization exhibits that LiNi0.5Mn1.5O4 nanorods are about 200–400xa0nm in diameter, and the RGO is well dispersed on the surface of LiNi0.5Mn1.5O4 nanorods. Moreover, a RGO layer coated on the surface of LiNi0.5Mn1.5O4 can suppress the interfacial side reactions. The electrochemical tests show that the RGO-LNMO composites reveal high specific capacity and excellent cyclic stability at high rates. The 1%-RGO-LNMO composite can still possess the capacity of 71.4xa0mAhxa0g−1 and excellent capacity retention about 99% after 1000xa0cycles at 10xa0C rate. The excellent performance of RGO-LNMO composites makes it a promising candidate as lithium-ion battery cathode materials.