Liying Bao

Spinel/Layered Heterostructured Cathode Material for High-Capacity and High-Rate Li-Ion Batteries

Best of both worlds: A heterostructured material is synthesized that comprises a core of layered lithium-rich material and an outer layer of nanospinel material. This spinel/layered heterostructured material maximizes the inherent advantages of the 3D Li(+) insertion/extraction framework of the spinel structure and the high Li(+) storage capacity of the layered structure. The material exhibits super-high reversible capacities, outstanding rate capability and excellent cycling ability.

Ultrathin Spinel Membrane-Encapsulated Layered Lithium-Rich Cathode Material for Advanced Li-Ion Batteries

Lack of high-performance cathode materials has become a technological bottleneck for the commercial development of advanced Li-ion batteries. We have proposed a biomimetic design and versatile synthesis of ultrathin spinel membrane-encapsulated layered lithium-rich cathode, a modification by nanocoating. The ultrathin spinel membrane is attributed to the superior high reversible capacity (over 290 mAh g(-1)), outstanding rate capability, and excellent cycling ability of this cathode, and even the stubborn illnesses of the layered lithium-rich cathode, such as voltage decay and thermal instability, are found to be relieved as well. This cathode is feasible to construct high-energy and high-power Li-ion batteries.

Hierarchical Li1.2Ni0.2Mn0.6O2 Nanoplates with Exposed {010} Planes as High‐Performance Cathode Material for Lithium‐Ion Batteries

Hierarchical Li1.2 Ni0.2 Mn0.6 O2 nanoplates with exposed {010} planes are designed and synthesized. In combination with the advantages from the hierarchical archi-tecture and the exposed electrochemically active {010} planes of layered materials, this material satisfies both efficient ion and electron transport and thus shows superior rate capability and excellent cycling stability.

Can surface modification be more effective to enhance the electrochemical performance of lithium rich materials

Lithium rich materials Li[Ni0.2Li0.2Mn0.6]O2 have been successfully modified by coating a thick layer of electrochemical active delithiated oxides MnOx (1.5 < x ≤ 2). The morphology observations and XRD results show that the thickness of coating layer of the modified sample 0.10MnOx·0.90Li[Ni0.2Li0.2Mn0.6]O2 is about 20 nm and there is a tiny amount of spinel structure in the coating layer. The electrochemical performance results indicate that the thick coated materials 0.10MnOx·0.90Li[Ni0.2Li0.2Mn0.6]O2 exhibit higher reversible capacity (265 mAh g−1 after 30 cycles), higher initial coulombic efficiency (90.2%), better low rate discharge capability (above 238 mAh g−1 at 1 C, 222 mAh g−1 at 2 C) and superior cycle-ability (30 cycles: 88.9%, subsequent 50 cycles after rest: 92.4%) than those of the pristine sample and conventional coated sample, respectively. The cycle voltammograms show good reversibility of the 0.10MnOx·0.90Li[Ni0.2Li0.2Mn0.6]O2 sample. The EIS tests reveal the charge transfer resistance of 0.10MnOx·0.90Li[Ni0.2Li0.2Mn0.6]O2 is lower than that of the pristine sample and conventional coated sample, respectively. Our research findings may provide significant new insights on surface modification of lithium rich cathode materials for the next generation of lithium ion batteries.

Effect of Ni2+ Content on Lithium/Nickel Disorder for Ni-Rich Cathode Materials

Li excess LiNi0.8Co0.1Mn0.1O2 was produced by sintering the Ni0.8Co0.1Mn0.1(OH)2 precursor with different amounts of a lithium source. X-ray photoelectron spectroscopy confirmed that a greater excess of Li(+) leads to an increase in the number of Ni(2+) ions. Interestingly, the level of Li(+)/Ni(2+) disordering decreases with an increase in Ni(2+) content determined by the I003/I104 ratio in the X-ray diffraction patterns. The electrochemical measurement shows that the cycling stability and rate capability improve with an increase in Ni(2+) content. After cycling, electrochemical impedance spectroscopy shows decreased charge transfer resistance, and the XRD patterns exhibit an increased I003/I104 ratio with an increase in Ni(2+) content, reflecting the decrease in the level of Li(+)/Ni(2+) disorder during cycling.

3D coral-like nitrogen-sulfur co-doped carbon-sulfur composite for high performance lithium-sulfur batteries

3D coral-like, nitrogen and sulfur co-doped mesoporous carbon has been synthesized by a facile hydrothermal-nanocasting method to house sulfur for Li–S batteries. The primary doped species (pyridinic-N, pyrrolic-N, thiophenic-S and sulfonic-S) enable this carbon matrix to suppress the diffusion of polysulfides, while the interconnected mesoporous carbon network is favourable for rapid transport of both electrons and lithium ions. Based on the synergistic effect of N, S co-doping and the mesoporous conductive pathway, the as-fabricated C/S cathodes yield excellent cycling stability at a current rate of 4 C (1 C = 1675 mA g−1) with only 0.085% capacity decay per cycle for over 250 cycles and ultra-high rate capability (693 mAh g−1 at 10 C rate). These capabilities have rarely been reported before for Li-S batteries.

The role of yttrium content in improving electrochemical performance of layered lithium-rich cathode materials for Li-ion batteries

The promising layered lithium-rich cathode materials, Li1.2Mn0.6−xNi0.2YxO2 (0 ≤ x ≤ 0.05), have been synthesized by substituting Mn4+ in Li1.2Mn0.6Ni0.2O2 with unusually large Y3+ ions, in order to improve their cycling performance and rate capability. An oxalate co-precipitation method is adopted in the synthetic process. X-ray diffraction (XRD) patterns show that, other than as a dopant, the yttrium element is found to become Y2O3 or LiYO2 in excess Y3+-doped samples. The effects of yttrium content on the electrochemical properties of the lithium-rich materials are investigated by electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge tests as well. It demonstrates that the high capacity retention (240.7 mA h g−1 after 40 cycles at 0.1 C rate) and superior rate capability (184.5 mA h g−1 after 40 cycles at 1 C rate) have been achieved by the lithium-rich materials with a suitable amount of Y3+ doping. The “super-large” Y3+ can expand Li+-diffusing channels in the layered structure and stabilize the material structure.

Role of Cobalt Content in Improving the Low-Temperature Performance of Layered Lithium-Rich Cathode Materials for Lithium-Ion Batteries.

Layered lithium-rich cathode material, Li1.2Ni0.2-xCo2xMn0.6-xO2 (x = 0-0.05) was successfully synthesized using a sol-gel method, followed by heat treatment. The effects of trace amount of cobalt doping on the structure, morphology, and low-temperature (-20 °C) electrochemical properties of these materials are investigated systematically. X-ray diffraction (XRD) results confirm that the Co has been doped into the Ni/Mn sites in the transition-metal layers without destroying the pristine layered structure. The morphological observations reveal that there are no changes of morphology or particle size after Co doping. The electrochemical performance results indicate that the discharge capacities and operation voltages are drastically lowered along with the decreasing temperature, but their fading rate becomes slower when increasing the Co contents. At -20 °C, the initial discharge capacity of sample with x = 0 could retain only 22.1% (57.3/259.2 mAh g(-1)) of that at 30 °C, while sample with x = 0.05 could maintain 39.4% (111.3/282.2 mAh g(-1)). Activation energy analysis and electrochemical impedance spectroscopy (EIS) results reveal that such an enhancement of low-temperature discharge capacity is originated from the easier interface reduction reaction of Ni(4+) or Co(4+) after doping trace amounts of Co, which decreases the activation energy of the charge transfer process above 3.5 V during discharging.

Enhanced Electrochemical Performance of Layered Lithium-Rich Cathode Materials by Constructing Spinel-Structure Skin and Ferric Oxide Islands

Layered lithium-rich cathode materials have been considered as competitive candidates for advanced lithium-ion batteries because they are environmentally benign, high capacity (more than 250 mAh·g-1), and low cost. However, they still suffer from poor rate capability and modest cycling performance. To address these issues, we have proposed and constructed a spinel-structure skin and ferric oxide islands on the surface of layered lithium-rich cathode materials through a facile wet chemical method. During the surface modification, Li ions in the surface area of pristine particles could be partially extracted by H+, along with the depositing process of ferric hydrogen. After calcination, the surface structure transformed to spinel structure, and ferric hydrogen was oxidized to ferric oxide. The as-designed surface structure was verified by EDX, HRTEM, XPS, and CV. The experimental results demonstrated that the rate performance and capacity retentions were significantly enhanced after such surface modification. The modified sample displayed a high discharge capacity of 166 mAh·g-1 at a current density of 1250 mA·g-1 and much more stable capacity retention of 84.0% after 50 cycles at 0.1C rate in contrast to 60.6% for pristine material. Our surface modification strategy, which combines the advantages of spinel structure and chemically inert ferric oxide nanoparticles, has been shown to be effective for realizing the layered lithium-rich cathodes with surface construction of fast ion diffusing capability as well as robust electrolyte corroding durability.

High performance FeFx/C composites as cathode materials for lithium-ion batteries

FeFx precursors were synthesized by a simplified one-step hydrothermal synthesis route with commercial Fe(OH)3 and HF as raw materials; then the as-prepared precursor was calcined in different temperature and obtained FeF3, FeF2, and amorphous mixture FeF3-FeF2. These materials were characterized by X-ray diffraction, scanning electron microscope, and X-ray photoelectron spectroscopy and used as cathode materials for lithium-ion batteries. The electrochemical tests show that the initial discharge capacities of FeF3, FeF2, and amorphous mixture FeF3-FeF2 are as high as 204.6 mAh/g, 162 mAh/g, and 208.6 mAh/g, respectively, at the rate of 0.1 C in the range 2.0-4.5 V at 25 °C, and display very excellent discharge capacity retention rate after the first discharge process. Furthermore, the cyclic voltammogram test was used to illustrate the reaction mechanisms of the nanocomposites.