Taolin Zhao

Multifunctional AlPO4 coating for improving electrochemical properties of low-cost Li[Li0.2Fe0.1Ni0.15Mn0.55]O2 cathode materials for lithium-ion batteries.

Layered Li-rich, Fe- and Mn-based cathode material, Li[Li0.2Fe0.1Ni0.15Mn0.55]O2, has been successfully synthesized by a coprecipitation method and further modified with different coating amounts of AlPO4 (3, 5, and 7 wt %). The effects of AlPO4 coating on the structure, morphology and electrochemical properties of these materials are investigated systematically. XRD results show that the pristine sample is obtained with typical Li-rich layered structure and trace amount of Li3PO4 phase are observed for the coated samples. The morphology observations reveal that all the samples show spherical particles (3-4 μm in diameter) with hierarchical structure, composed of nanoplates and nanoparticles. XPS analysis confirms the existence of AlPO4 and Li3PO4 phases at the surface. The electrochemical performance results indicate that the sample coated with 5 wt % AlPO4 exhibits the highest reversible capacity (220.4 mA h g(-1) after 50 cycles at 0.1C), best cycling performance (capacity retention of 74.4% after 50 cycles at 0.1C) and rate capability (175.3 mA h g(-1) at 1C, and 120.2 mA h g(-1) at 10C after 100 cycles) among all the samples. Cycle voltammograms show good reversibility of the coated samples. EIS analysis reveals that charge transfer resistance after coating is much lower than that of the pristine sample. The excellent electrochemical performances can be attributed to the effects of multifunctional AlPO4 coating layer, including the suppression of surface side reaction and oxygen vacancies diffusion, the acceleration of lithium ions transport as well as the lower electrochemical resistance. Our research provides a new insight of surface modification on low-cost Li-rich material to achieve high energy as the next-generation cathode of lithium-ion batteries.

The Positive Roles of Integrated Layered-Spinel Structures Combined with Nanocoating in Low-Cost Li-Rich Cathode Li[Li0.2Fe0.1Ni0.15Mn0.55]O2 for Lithium-Ion Batteries

As the most promising cathodes of lithium-ion batteries, lithium-rich manganese-based layered oxides with high capacity suffer from poor cycle stability, poor rate capability, and fast voltage fading. Here we introduced AlF3 into the surface of layered lithium-rich cathode (Li[Li0.2Fe0.1Ni0.15Mn0.55]O2) as an artificial protective layer as well as an inducer of integrated layered-spinel structures to achieve both low cost and high capacity. The reduced irreversible capacity loss, improved cycling stability, and superior high-rate capability were ascribed to the combination of AlF3 nanocoating and the unique structures as well as the low charge transfer resistance. Besides, the intractable issue, fast voltage fading of the layered lithium-rich cathode was also alleviated. Such materials with both low cost and high capacity are considered to be promising candidate cathodes to achieve lithium-ion batteries with high energy and high power.

Hierarchical mesoporous/macroporous Co3O4 ultrathin nanosheets as free-standing catalysts for rechargeable lithium–oxygen batteries

Hierarchical mesoporous/macroporous Co3O4 ultrathin nanosheets were synthesized as free-standing catalysts for rechargeable Li–O2 batteries. The Co3O4 nanosheets were directly grown on nickel foam through a simple hydrothermal reaction, followed by a calcination process. The impact of solvents used in the hydrothermal reaction on the morphology of catalysts has been investigated. The results showed that the prepared Co3O4 catalyst synthesized with ethylene glycol and deionized water (1 : 1 in volume) presented a much better electrochemical performance with a capacity of 11 882 mA h g−1 under a current density of 100 mA g−1 during the initial discharge and good cycling stability (more than 80 cycles at 200 mA g−1 with the capacity limited to 500 mA h g−1). Meanwhile, the charge potential was significantly reduced to ca. 3.7 V. It is interesting to find that the morphology of the discharge product, Li2O2 could be changed by controlling the shape of catalysts. The impacts of the hierarchical mesoporous/macroporous nanosheet structure on the performance of Li–O2 batteries have been discussed.

Advanced cathode materials for lithium-ion batteries using nanoarchitectonics

In recent years, the global climate has further deteriorated because of the excessive consumption of traditional energy sources. The replacement of traditional fossil fuels with limited reserves by alternative energy sources has become one of the main strategies to alleviate the increasingly serious environmental issues. As a sustainable and promising store of renewable energy, lithium-ion batteries have replaced other types of batteries for many small-scale consumer devices. Notwithstanding their worldwide applications, it has become abundantly clear that the design and fabrication of electrode materials is urgently required to adapt to meet the growing global demand for energy and the power densities needed to make electric vehicles fully commercially viable. To dramatically enhance battery performance, further advances in materials chemistry are essential, especially in novel nanomaterials chemistry. The construction of nanostructured cathode materials by reducing particle size can boost electrochemical performance. The present review is intended to provide readers with a better understanding of the unique contribution of various nanoarchitectures to lithium-ion batteries over the last decade. Nanostructured cathode materials with different dimensions (0D, 1D, 2D, and 3D), morphologies (hollow, core-shell, etc.), and composites (mainly graphene-based composites) are highlighted, aiming to unravel the opportunities for the development of future-generation lithium-ion batteries. The advantages and challenges of nanomaterials are also addressed in this review. We hope to simulate many more extensive and insightful studies on nanoarchitectonic cathode materials for advanced lithium-ion batteries with desirable performance.

Surface modification of a cobalt-free layered Li[Li0.2Fe0.1Ni0.15Mn0.55]O2 oxide with the FePO4/Li3PO4 composite as the cathode for lithium-ion batteries

A low-cost, layered Li[Li0.2Fe0.1Ni0.15Mn0.55]O2 oxide is successfully coated with the FePO4/Li3PO4 composite by an aqueous solution method to achieve high electrochemical performance. X-ray diffraction (XRD) patterns indicate that the modified sample is a hexagonal phase with a minor crystalline Li3PO4 phase inside. Compared with the pristine sample, the modified ones show no change in morphology characterized by scanning electron microscopy (SEM) analysis. However, a uniform coating layer of the FePO4/Li3PO4 composite can be observed clearly in the transmission electron microscopy (TEM) images. By electrochemical characterization, the composite coating layer is proved to be beneficial for improving the reversible capacity and cycling stability of the modified sample (a higher reversible discharge capacity of 192 mA h g−1 after 50 cycles with a 3 wt% coating amount). Surprisingly, the high-rate capability is also observed to be improved with a 3 wt% coating amount (125.3 mA h g−1 after 100 cycles at 10 C). Furthermore, the voltage decay phenomenon during cycling is slowed down greatly and thus phase transformation is suppressed by the composite coating layer. These results are attributed to the suppression of the bulk material from direct exposure to the electrolyte by the amorphous FePO4 coating component and the good Li+ transport through the Li3PO4 coating component. The prepared modified materials can meet the requirements of low cost and high performance in various applications for lithium-ion batteries.

Organic-Acid-Assisted Fabrication of Low-Cost Li-Rich Cathode Material (Li[Li1/6Fe1/6Ni1/6Mn1/2]O2) for Lithium–Ion Battery

A novel Li-rich cathode Li[Li1/6Fe1/6Ni1/6Mn1/2]O2 (0.4Li2MnO3-0.6LiFe1/3Ni1/3Mn1/3O2) was synthesized by a sol-gel method, which uses citric acid (SC), tartaric acid (ST), or adipic acid (SA) as a chelating agent. The structural, morphological, and electrochemical properties of the prepared samples were characterized by various methods. X-ray diffraction showed that single-phase materials are formed mainly with typical α-NaFeO2 layered structure (R3̅m), and the SC sample has the lowest Li/Ni cation disorder. The morphological study indicated homogeneous primary particles in good distribution size (100 nm) with small aggregates. The Fe, Ni, and Mn valences were determined by X-ray absorption near-edge structure analysis. In coin cell tests, the initial reversible discharge capacity of an SA electrode was 289.7 mAh g(-1) at the 0.1C rate in the 1.5-4.8 V voltage range, while an SC electrode showed a better cycling stability with relatively high capacity retention. At the 2C rate, the SC electrode can deliver a discharge capacity of 150 mAh g(-1) after 50 cycles. Differential capacity vs voltage curves were employed to further investigate the electrochemical reactions and the structural change process during cycling. This low-cost, Fe-based compound prepared by the sol-gel method has the potential to be used as the high capacity cathode material for Li-ion batteries.

Template-Assisted Hydrothermal Synthesis of Li2MnSiO4 as a Cathode Material for Lithium Ion Batteries

Lithium manganese silicate (Li2MnSiO4) is an attractive cathode material with a potential capacity above 300 mA h g(-1) if both lithium ions can be extracted reversibly. Two drawbacks of low electronic conductivity and structural collapse could be overcome by a conductive surface coating and a porous structure. Porous morphology with inner mesopores offers larger surface area and shorter ions diffusion pathways and also buffers the volume changes during lithium insertion and extraction. In this paper, mesoporous Li2MnSiO4 (M-Li2MnSiO4) prepared using MCM-41 as template through a hydrothermal route is compared to a sample of bulk Li2MnSiO4 (B-Li2MnSiO4) using silica as template under the same conditions. Also, in situ carbon coating technique was used to improve the electronic conductivity of M-Li2MnSiO4. The physical properties of these cathode materials were further characterized by SEM, XRD, FTIR, and N2 adsorption-desorption. It is shown that M-Li2MnSiO4 exhibits porous structure with pore sizes distributed in the range 9-12 nm, and when used as cathode electrode material, M-Li2MnSiO4 exhibits enhanced specific discharge capacity of 193 mA h g(-1) at a constant current of 20 mA g(-1) compared with 120.1 mA h g(-1) of B-Li2MnSiO4. This is attributed to the porous structure which allows the electrolyte to penetrate into the particles easily. And carbon-coated M-Li2MnSiO4 shows smaller charge transfer resistance and higher capacity of 217 mA h g(-1) because carbon coating retains the porous structure and enhances the electrical conductivity.

Structure Evolution from Layered to Spinel during Synthetic Control and Cycling Process of Fe-Containing Li-Rich Cathode Materials for Lithium-Ion Batteries

As promising cathode materials for lithium-ion batteries (LIBs), Fe-containing Li-rich compounds of Li1+xFe0.1Ni0.15Mn0.55Oy (0 ≤ x ≤ 0.3 and 1.9 ≤ y ≤ 2.05) have been successfully synthesized by calcining the spherical precursors with appropriate amounts of lithium carbonate. The structures, morphologies, and chemical states of these compounds are characterized to better understand the corresponding electrochemical performances. With an increase of lithium content, Li1+xFe0.1Ni0.15Mn0.55Oy evolves from a complex layered-spinel structure to a layered structure. The lithium content also affects the average size and adhesion of the primary particles. At 0.1 C, sample x = 0.1 shows the highest first charge/discharge specific capacities (338.7 and 254.3 mA h g–1), the highest first Coulombic efficiency (75.1%), the lowest first irreversible capacity loss (84.4 mA h g–1), the highest reversible discharge specific capacity, and good rate capability. Notably, voltage fading can be alleviated through the adjustment of structural features. Such superior electrochemical performances of sample x = 0.1 are ascribed to the hierarchical micro-/nanostructure, the harmonious existence of complex layered-spinel phase, and the low charge-transfer resistance. An integral view of structure evolution from layered to spinel during synthetic control and cycling process is provided to broaden the performance scope of Li–Fe–Ni–Mn–O cathodes for LIBs.