Synthesis of hierarchical conductive C/LiFePO 4 /carbon nanotubes composite with less antisite defects for high power lithium-ion batteries

Correlation Between Li-Fe Anti-Site and Memory Effect of LiFePO4 in Li-Ion Batteries

In Li-ion batteries, the origin of memory effect in Al-doped Li4Ti5O12 has been revealed as the reversible Al-ion switching between 8a and 16c sites in the spinel structure, but it is still not clear about that for olivine LiFePO4, which is one of the most important cathode materials. In this work, a series of Na-doped and Ti-doped LiFePO4 are prepared in a high-temperature solid-state method, electrochemically investigated in Li-ion batteries and characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS NMR). Compared with non-doped LiFePO4, the Ti doping can simultaneously suppress the memory effect and the Li-Fe anti-site, while they are simultaneously enhanced by the Na doping. Meanwhile, the Ti doping improves the electrochemical performance of LiFePO4, opposite to the Na doping. Accordingly, a schematic diagram of phase transition is proposed to interpret the memory effect of LiFePO4, in which the memory effect is attributed to the defect of Li-Fe anti-site.

Long-Life Regenerated LiFePO4 from Spent Cathode by Elevating the d-Band Center of Fe

A large amount of spent LiFePO₄ (LFP) has been produced in recent years because it is one of the most widely used cathode materials for electric vehicles. The traditional hydrometallurgical and pyrometallurgical recycling methods are doubted because of the economic and environmental benefits; the direct regeneration method is considered a promising way to recycle spent LFP. However, the performance of regenerated LFP by direct recycling is not ideal due to the migration of Fe ions during cycling and irreversible phase transition caused by sluggish Li⁺ diffusion. The key to addressing the challenge is to immobilize Fe atoms in the lattice and improve the Li⁺ migration capability during cycling. In this work, spent LFP is regenerated by using environmentally friendly ethanol, and its cycling stability is promoted by elevating the d-band center of Fe atoms via construction of a heterogeneous interface between LFP and nitrogen-doped carbon. The FeO bonding is strengthened and the migration of Fe ions during cycling is suppressed due to the elevated d-band center. The Li⁺ diffusion kinetics in the regenerated LFP are improved, leading to an excellent reversibility of the phase transition. Therefore,  the regenerated LFP exhibits an ultrastable cycling performance at a high rate of 10 C with ≈80% capacity retention after 1000 cycles.

Interlayer-Expanded MoS2 Nanoflowers Vertically Aligned on MXene@Dual-Phased TiO2 as High-Performance Anode for Sodium-Ion Batteries

As a promising energy-storage and conversion anode material for high-power sodium-ion batteries operated at room temperature, the practical application of layered molybdenum disulfide (MoS₂) is hindered by volumetric expansion during cycling. To address this issue, a rational design of MoS₂ with enlarged lattice spacing aligned vertically on hierarchically porous Ti₃C₂T_x MXene nanosheets with partially oxidized rutile and anatase dual-phased TiO₂ (MoS₂@MXene@D-TiO₂) composites via one-step hydrothermal method without following anneal process is reported. This unique "plane-to-surface" structure accomplishes hindering MoS₂ from aggregating and restacking, enabling sufficient electrode/electrolyte interaction simultaneously. Meanwhile, the heterogeneous structure among dual-phased TiO₂, MoS₂, and MXene could constitute a built-in electric field, promoting high Na⁺ transportation. As a result, the as-constructed 3D MoS₂@MXene@D-TiO₂ heterostructure delivers admirable high-rate reversible capacity (359.6 mAh g^-1 up to 5 A g^-1) at room temperature, excellent cycling stability (about 200 mAh g^-1) at a low temperature of -30 °C, and superior electrochemical performance in Na⁺ full batteries by coupling with a Na₃V₂(PO₄)₃ cathode. This ingenious design is clean and facile to inspire the potential of advanced low-dimensional heterogeneous structure electrode materials in the application of high-performance sodium-ion batteries.

Controlled Hydrothermal/Solvothermal Synthesis of High-Performance LiFePO4 for Li-Ion Batteries

The sluggish Li-ion diffusivity in LiFePO₄ , a famous cathode material, relies heavily on the employment of a broad spectrum of modifications to accelerate the slow kinetics, including size and orientation control, coating with electron-conducting layer, aliovalent ion doping, and defect control. These strategies are generally implemented by employing the hydrothermal/solvothermal synthesis, as reflected by the hundreds of publications on hydrothermal/solvothermal synthesis in recent years. However, LiFePO₄ is far from the level of controllable preparation, due to the lack of the understanding of the relations between the synthesis condition and the nucleation-and-growth of LiFePO₄ . In this paper, the recent progress in controlled hydrothermal/solvothermal synthesis of LiFePO₄ is first summarized, before an insight into the relations between the synthesis condition and the nucleation-and-growth of LiFePO₄ is obtained. Thereafter, a review over surface decoration, lattice substitution, and defect control is provided. Moreover, new research directions and future trends are also discussed.

NiO@MnO2 core–shell composite microtube arrays for high-performance lithium ion batteries

The NiO@MnO₂ core–shell microtube array electrode with excellent lithium storage performance is fabricated by self-corrosion and electrodeposition.

Enhancement of the Rate Capability of LiFePO4 by a New Highly Graphitic Carbon-Coating Method

Low lithium ion diffusivity and poor electronic conductivity are two major drawbacks for the wide application of LiFePO4 in high-power lithium ion batteries. In this work, we report a facile and efficient carbon-coating method to prepare LiFePO4/graphitic carbon composites by in situ carbonization of perylene-3,4,9,10-tetracarboxylic dianhydride during calcination. Perylene-3,4,9,10-tetracarboxylic dianhydride containing naphthalene rings can be easily converted to highly graphitic carbon during thermal treatment. The ultrathin layer of highly graphitic carbon coating drastically increased the electronic conductivity of LiFePO4. The short pathway along the [010] direction of LiFePO4 nanoplates could decrease the Li(+) ion diffusion path. In favor of the high electronic conductivity and short lithium ion diffusion distance, the LiFePO4/graphitic carbon composites exhibit an excellent cycling stability at high current rates at room temperature and superior performance at low temperature (-20 °C).