Hongyuan Zhao

Er-Doped LiNi0.5Mn1.5O4 Cathode Material with Enhanced Cycling Stability for Lithium-Ion Batteries

The Er-doped LiNi0.5Mn1.5O4 (LiNi0.495Mn1.495Er0.01O4) sample was successfully prepared by citric acid-assisted sol-gel method with erbium oxide as an erbium source for the first time. Compared with the undoped sample, the Er-doped LiNi0.5Mn1.5O4 sample maintained the basic spinel structure, suggesting that the substitution of Er3+ ions for partial nickel and manganese ions did not change the intrinsic structure of LiNi0.5Mn1.5O4. Moreover, the Er-doped LiNi0.5Mn1.5O4 sample showed better size distribution and regular octahedral morphology. Electrochemical measurements indicated that the Er-doping could have a positive impact on the electrochemical properties. When cycled at 0.5 C, the Er-doped LiNi0.5Mn1.5O4 sample exhibited an initial discharge capacity of 120.6 mAh·g−1, and the capacity retention of this sample reached up to 92.9% after 100 cycles. As the charge/discharge rate restored from 2.0 C to 0.2 C, the discharge capacity of this sample still exhibited 123.7 mAh·g−1 with excellent recovery rate. Since the bonding energy of Er-O (615 kJ·mol−1) was higher than that of Mn-O (402 kJ·mol −1) and Ni-O (392 kJ·mol−1), these outstanding performance could be attributed to the increased structure stability as well as the reduced aggregation behavior and small charge transfer resistance of the Er-doped LiNi0.5Mn1.5O4.

Enhanced Cycling Stability of LiCuxMn1.95−xSi0.05O4 Cathode Material Obtained by Solid-State Method

The LiCuxMn1.95−xSi0.05O4 (x = 0, 0.02, 0.05, 0.08) samples have been obtained by a simple solid-state method. XRD and SEM characterization results indicate that the Cu-Si co-doped spinels retain the inherent structure of LiMn2O4 and possess uniform particle size distribution. Electrochemical tests show that the optimal Cu-doping amount produces an obvious improvement effect on the cycling stability of LiMn1.95Si0.05O4. When cycled at 0.5 C, the optimal LiCu0.05Mn1.90Si0.05O4 sample exhibits an initial capacity of 127.3 mAh g−1 with excellent retention of 95.7% after 200 cycles. Moreover, when the cycling rate climbs to 10 C, the LiCu0.05Mn1.90Si0.05O4 sample exhibits 82.3 mAh g−1 with satisfactory cycling performance. In particular, when cycled at 55 °C, this co-doped sample can show an outstanding retention of 94.0% after 100 cycles, whiles the LiMn1.95Si0.05O4 only exhibits low retention of 79.1%. Such impressive performance shows that the addition of copper ions in the Si-doped spinel effectively remedy the shortcomings of the single Si-doping strategy and the Cu-Si co-doped spinel can show excellent cycling stability.

A Simple, Quick and Eco-Friendly Strategy of Synthesis Nanosized α-LiFeO2 Cathode with Excellent Electrochemical Performance for Lithium-Ion Batteries

Nanosized α-LiFeO2 samples were successfully synthesized via a simple, quick and eco-friendly strategy at ambient temperature followed by a low temperature calcined process. X-ray diffraction (XRD), scanning electronic microscopy (SEM) and transmission electron microscopy (TEM) measurements revealed that the optimal α-LiFeO2 sample was composed of extremely small nanoparticles. The electrochemical properties were tested at 0.1 C in the cut-off voltage of 1.5–4.8 V. The sample obtained at 150 °C for 6 h exhibited the best cycling stability with high initial discharge capacity of 223.2 mAh/g, which was extremely high for pristine α-LiFeO2 without any modification process. After 50 cycles, the discharge capacity could still maintain 194.5 mAh/g with good capacity retention. When the charge–discharge rate increased to 0.2 C and 0.5 C, the initial discharge capacities were 216.6 mAh/g and 171.5 mAh/g, respectively. Furthermore, the optimal sample showed low charge transfer resistance and high lithium-ion diffusion coefficients, which facilitated the excellent electrochemical performance.

Sol-Gel Synthesis of Silicon-Doped Lithium Manganese Oxide with Enhanced Reversible Capacity and Cycling Stability

A series of silicon-doped lithium manganese oxides were obtained via a sol-gel process. XRD characterization results indicate that the silicon-doped samples retain the spinel structure of LiMn2O4. Electrochemical tests show that introducing silicon ions into the spinel structure can have a great effect on reversible capacity and cycling stability. When cycled at 0.5 C, the optimal Si-doped LiMn2O4 can exhibit a pretty high initial capacity of 140.8 mAh g−1 with excellent retention of 91.1% after 100 cycles, which is higher than that of the LiMn2O4, LiMn1.975Si0.025O4, and LiMn1.925Si0.075O4 samples. Moreover, the optimal Si-doped LiMn2O4 can exhibit 88.3 mAh g−1 with satisfactory cycling performance at 10 C. These satisfactory results are mainly contributed by the more regular and increased MnO6 octahedra and even size distribution in the silicon-doped samples obtained by sol-gel technology.

Enhanced Cycling Stability through Erbium Doping of LiMn2O4 Cathode Material Synthesized by Sol-Gel Technique

In this work, LiMn2−xErxO4 (x ≤ 0.05) samples were obtained by sol-gel processing with erbium nitrate as the erbium source. XRD measurements showed that the Er-doping had no substantial impact on the crystalline structure of the sample. The optimal LiMn1.97Er0.03O4 sample exhibited an intrinsic spinel structure and a narrow particle size distribution. The introduction of Er3+ ions reduced the content of Mn3+ ions, which seemed to efficiently suppress the Jahn–Teller distortion. Moreover, the decreased lattice parameters suggested that a more stable spinel structure was obtained, because the Er3+ ions in a ErO6 octahedra have stronger bonding energy (615 kJ/mol) than that of the Mn3+ ions in a MnO6 octahedra (402 kJ/mol). The present results suggest that the excellent cycling life of the optimal LiMn1.97Er0.03O4 sample is because of the inhibition of the Jahn-Teller distortion and the improvement of the structural stability. When cycled at 0.5 C, the optimal LiMn1.97Er0.03O4 sample exhibited a high initial capacity of 130.2 mAh g−1 with an excellent retention of 95.2% after 100 cycles. More significantly, this sample showed 83.1 mAh g−1 at 10 C, while the undoped sample showed a much lower capacity. Additionally, when cycled at 55 °C, a satisfactory retention of 91.4% could be achieved at 0.5 C after 100 cycles with a first reversible capacity of 130.1 mAh g−1.

Wear Resistance Mechanism of Alumina Ceramics Containing Gd2O3

Excellent wear resistance of alumina ceramics is a desirable quality for many products. The purpose of this work was to improve the wear resistance of 99% alumina ceramics in an Al2O3–Gd2O3–SiO2–CaO–MgO (AGSCM) system. The content of Gd2O3 varied from 0.01% to 1%. A test of wear rate was performed in a ball milling apparatus in a water environment according to the Chinese industry standard. The compositions and microstructure of this material, as well as the effect of bulk density on wear rate, were studied. The effect of Gd2O3 on phases, grain growth mode, and grain boundary cohesion was investigated. It was found that Gd2O3 could refine grain size, form compressive stress of the grain boundary, and promote the crystallization of CaAl12O19. The wear rate of this material was as low as 0.00052‰ (the Chinese industry standard wear rate is ≤0.15‰). The mechanisms for wear resistance of AGSCM ceramics were also determined.