Mesoporous LiFePO4 Microspheres Embedded Homogeneously with 3D CNT Conductive Networks for Enhanced Electrochemical Performance

Design of LiFePO4 and porous carbon composites with excellent High-Rate charging performance for Lithium-Ion secondary battery

Lithium iron phosphate (LFP) is one of the promising cathode materials of lithium ion battery (LIB), but poor electrical conductivity restricts its electrochemical performance. Carbon coating can improve electrical conductivity of LFP without changing its intrinsic property. Uniform coating of carbon on LFP is significant to avoid charge congregation and unpreferable redox reactions. It is the first time to apply the commercial organic binder, Super P® (SP), as carbon source to achieve uniform coating on LFP as cathode material of LIB. The simple and economical mechanofusion method is firstly applied to coat different amounts of SP on LFP. The LIB with the cathode material of optimized SP-coated LFP shows the highest capacity of 165.6 mAh/g at 0.1C and 59.8 mAh/g at 10C, indicating its high capacity and excellent high-rate charge/discharge capability. SP is applied on other commercial LFP materials, M121 and M23, for carbon coating. Enhanced high-rate charge/discharge capabilities are also achieved for LIB with SP-coated M121 and M23 as cathode materials. This new material and technique for carbon coating is verified to be applicable on different LFP materials. This novel carbon coating method is expected to apply on other cathode materials of LIB with outstanding electrochemical performances.

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.

Superior electrochemical performance of a novel LiFePO4/C/CNTs composite for aqueous rechargeable lithium-ion batteries

Olivine LiFePO₄ covered flocculent carbon layers wrapped with carbon nanotubes (CNTs) prepared by sol-gel method and calcination is used as the cathode material for aqueous rechargeable lithium-ion batteries (ARLBs). The phase structures and morphologies of the composite material are characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), and transmission electron microscopy (TEM). The mechanism and method through which CNTs and flocculent carbon improve the electrochemical performance are investigated in an aqueous lithium-ion battery by setting up a comparative experiment. The ARLB system is assembled using a LiFePO₄/C/CNTs cathode and a zinc anode in 1 mol L^-1 ZnSO₄·7H₂O and saturated LiNO₃ aqueous solution (pH = 6), which can deliver a capacity of 158 mA h g^-1 at a rate of 1C. Even at a rate of 50C, it still has a capacity of 110 mA h g^-1 after 250 cycles with fantastic capacity retention (95.7%). The lithium-ion diffusion coefficient increases by an order of magnitude due to the addition of CNTs together with flocculent carbon. Four LEDs are successfully powered by the ARLBs for more than one minute to demonstrate the practical application. The excellent rate capabilities and thrilling discharge capacity at a high rate indicate that this cathode material possesses excellent electrochemical performance, and this ARLB system exhibits excellent potential as a power source for environmental applications.

Rapid preparation of high electrochemical performance LiFePO4/C composite cathode material with an ultrasonic-intensified micro-impinging jetting reactor

A joint chemical reactor system referred to as an ultrasonic-intensified micro-impinging jetting reactor (UIJR), which possesses the feature of fast micro-mixing, was proposed and has been employed for rapid preparation of FePO₄ particles that are amalgamated by nanoscale primary crystals. As one of the important precursors for the fabrication of lithium iron phosphate cathode, the properties of FePO₄ nano particles significantly affect the performance of the lithium iron phosphate cathode. Thus, the effects of joint use of impinging stream and ultrasonic irradiation on the formation of mesoporous structure of FePO₄ nano precursor particles and the electrochemical properties of amalgamated LiFePO₄/C have been investigated. Additionally, the effects of the reactant concentration (C=0.5, 1.0 and 1.5molL^-1), and volumetric flow rate (V=17.15, 51.44, and 85.74mLmin^-1) on synthesis of FePO₄·2H₂O nucleus have been studied when the impinging jetting reactor (IJR) and UIJR are to operate in nonsubmerged mode. It was affirmed from the experiments that the FePO₄ nano precursor particles prepared using UIJR have well-formed mesoporous structures with the primary crystal size of 44.6nm, an average pore size of 15.2nm, and a specific surface area of 134.54m²g^-1 when the reactant concentration and volumetric flow rate are 1.0molL^-1 and 85.74mLmin^-1 respectively. The amalgamated LiFePO₄/C composites can deliver good electrochemical performance with discharge capacities of 156.7mAhg^-1 at 0.1C, and exhibit 138.0mAhg^-1 after 100 cycles at 0.5C, which is 95.3% of the initial discharge capacity.

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).

In situ catalytic synthesis of high-graphitized carbon-coated LiFePO4 nanoplates for superior Li-ion battery cathodes

The low electronic conductivity and one-dimensional diffusion channel along the b axis for Li ions are two major obstacles to achieving high power density of LiFePO4 material. Coating carbon with excellent conductivity on the tailored LiFePO4 nanoparticles therefore plays an important role for efficient charge and mass transport within this material. We report here the in situ catalytic synthesis of high-graphitized carbon-coated LiFePO4 nanoplates with highly oriented (010) facets by introducing ferrocene as a catalyst during thermal treatment. The as-obtained material exhibits superior performances for Li-ion batteries at high rate (100 C) and low temperature (-20 °C), mainly because of fast electron transport through the graphitic carbon layer and efficient Li(+)-ion diffusion through the thin nanoplates.

Nitrogen-doped carbon coated LiFePO4/carbon nanotube interconnected nanocomposites for high performance lithium ion batteries

High performance conductive networks, which were fabricated from a nitrogen-doped carbon layer and 3D CNT networks, have been prepared.