高比能LiFePO4的制备及性能研究

应用液相沉淀法-固相烧结法制备高密度的LiFePO4/C及纯相LiFePO4.X射线衍射、扫描电镜、傅立叶红外光谱仪、电化学性能测试表明:该样品具有单一的橄榄石结构和3.4 V左右的放电平台,掺碳的LiFe-PO4具有更优良的性能,粒度较小粒径分布均匀,振实密度达1.46 g/cm3,0.1C首次放电比容量为144.6mAh/g,循环20次后容量保持率为93.2%,1C倍率首次放电比容量为133.5 mAh/g,循环20次后容量下降8.76%.     

Magnetite/carbon core-shell nanorods as anode materials for lithium-ion batteries

Carbon coated magnetite (Fe₃O₄) core-shell nanorods were synthesized by a hydrothermal method using Fe₂O₃ nanorods as the precursor. Transmission electron spectroscopy (TEM) and high resolution TEM (HRTEM) analysis indicated that a carbon layer was coated on the surfaces of the individual Fe₃O₄ nanorods. The electrochemical properties of Fe₃O₄/carbon nanorods as anodes in lithium-ion cells were evaluated by cyclic voltammetry, ac impedance spectroscopy, and galvanostatic charge/discharge techniques. The as-prepared Fe₃O₄/C core-shell nanorods show an initial lithium storage capacity of 1120 mAh/g and a reversible capacity of 394 mAh/g after 100 cycles, demonstrating better performance than that of the commercial graphite anode material.     

SnS2–graphene nanocomposites as anodes of lithium-ion batteries

SnS₂–graphene nanocomposites are synthesized by a hydrothermal method, and their application as anodes of lithium-ion batteries has been investigated. SnS₂ nanosheets are uniformly coating on the surface of graphene. SnS₂–graphene nanocomposites exhibit high cyclability and capacity. The reversible capacity is 766 mAh/g at 0.2C rate and maintains at 570 mAh/g after 30 cycles. Such a high performance can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect between graphene and SnS₂ nanostructures. The present results indicate that SnS₂–graphene nanocomposites have potential applications in lithium-ion battery anodes.     

A sodium vanadium three-fluorophosphate cathode for rechargeable batteries synthesized by carbothermal reduction

Na₃V₂(PO₄)₂F₃, which could be used as cathode in Na-ion or Li-ion rechargeable batteries, was synthesized by carbothermal reduction (CTR) method at 700 °C with coralline structure by SEM analysis. The Na₃V₂(PO₄)₂F₃ cathode in Li-ion battery displayed an appreciable capacity of 188 mAh/g with a discharge plateau at 3.7 V under close-to-equilibrium galvanostatic conditions illuminating the feasible extraction of three Na ions per unit, and 130 mAh/g with retention of 96.8% after 37 cycles at 0.1 C. The NASICON-type structure could produce a large diffusion coefficient due to the three-dimensional framework, but cause a low conductivity and OCV around 3 V. The cathode could reach 188 mAh/g at 0.1 C, with a more 20 mAh/g at 3.7 V after washing by distilled water.     

Preparation and characterization of high-rate and long-cycle LiFePO4/C nanocomposite as cathode material for lithium-ion battery

Olivine LiFePO₄/C nanocomposite cathode materials with small-sized particles and a unique electrochemical performance were successfully prepared by a simple solid-state reaction using oxalic acid and citric acid as the chelating reagent and carbon source. The structure and electrochemical properties of the samples were investigated. The results show that LiFePO₄/C nanocomposite with oxalic acid (oxalic acid: Fe²⁺= 0.75:1) and a small quantity of citric acid are single phase and deliver initial discharge capacity of 122.1 mAh/g at 1 C with little capacity loss up to 500 cycles at room temperature. The rate capability and cyclability are also outstanding at elevated temperature. When charged/discharged at 60 °C, this materials present excellent initial discharge capacity of 148.8 mAh/g at 1 C, 128.6 mAh/g at 5 C, and 115.0 mAh/g at 10 C, respectively. The extraordinarily high performance of LiFePO₄/C cathode materials can be exploited suitably for practical lithium-ion batteries.     

Synthesis and characterization of core–shell F-doped LiFePO<Subscript>4</Subscript>/C composite for lithium-ion batteries

Core–shell LiFePO₄/C composite was synthesized via a sol–gel method and doped by fluorine to improve its electrochemical performance. Structural characterization shows that F⁻ ions were successfully introduced into the LiFePO₄ matrix. Transmission electron microscopy verifies that F-doped LiFePO₄/C composite was composed of nanosized particles with a ~3 nm thick carbon shell coating on the surface. As a cathode material for lithium-ion batteries, the F-doped LiFePO₄/C nanocomposite delivers a discharge capacity of 162 mAh/g at 0.1 C rate. Moreover, the material also shows good high-rate capability, with discharge capacities reaching 113 and 78 mAh/g at 10 and 40 C current rates, respectively. When cycled at 20 C, the cell retains 86% of its initial discharge capacity after 400 cycles, demonstrating excellent high-rate cycling performance.     

NiSe2 nanoparticles encapsulated in CNTs covered and N-doped TiN/carbon nanofibers as a binder-free anode for advanced sodium-ion batteries

Metal selenides are promising anodes for sodium-ion batteries (SIBs) due to the high theoretical capacity through conversion reaction mechanism. However, developing metal selenides with superior electrochemical sodium-ion storage performance is still a great challenge. In this work, a novel composite material of free-standing NiSe₂ nanoparticles encapsulated in N-doped TiN/carbon composite nanofibers with carbon nanotubes (CNTs) in-situ grown on the surface (NiSe₂@N-TCF/CNTs) is prepared by electrospinning and pyrolysis technique. In this composite materials, NiSe₂ nanoparticles on the surface of carbon nanofibers were encapsulated into CNTs, thus avoiding aggregation. The in-situ grown CNTs not only improve the conductivity but also act as a buffer to accommodate the volume expansion. TiN inside the nanofibers further enhances the conductivity and structural stability of carbon-based nanofibers. When directly used as anode for SIBs, the NiSe₂@N-TCF/CNT electrode delivered a reversible capacity of 392.1 mAh/g after 1000 cycles and still maintained 334.4 mAh/g even at a high rate of 2 A/g. The excellent sodium-ion storage performance can be attributed to the fast Na⁺ diffusion and transfer rate and the pseudocapacitance dominated charge storage mechanism, as is evidenced by kinetic analysis. The work provides a novel approach to the fabrication of high-performance anode materials for other batteries.     

Synthesis, characterization, and electrochemical performance of LiFePO4/C cathode materials for lithium ion batteries using various carbon sources: best results by using polystyrene nano-spheres

Olivine LiFePO₄/C cathode materials for lithium ion batteries were synthesized using monodisperse polystyrene (PS) nano-spheres and other carbon sources. The structure, morphology, and electrochemical performance of LiFePO₄/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge tests, electrochemical impedance spectroscopy (EIS) measurements, and Raman spectroscopy measurements. The results demonstrated that LiFePO₄/C materials have an ordered olivine-type structure with small particle sizes. Electrochemical analyses showed that the LiFePO₄/C cathode material synthesized from 7 wt.% PS nano-spheres delivers an initial discharge capacity of 167 mAh g^-1 (very close to the theoretical capacity of 170 mAh g^-1) at 0.1 C rate cycled between 2.5 and 4.1 V with excellent capacity retention after 50 cycles. According to Raman spectroscopy and EIS analysis, this composite had a lower I _D/I _G, sp ³/sp ² peak ratio, charge transfer resistance, and a higher exchange current density, indicating an improved electrochemical performance, due to the increased proportion of graphite-like carbon formed during pyrolysis of PS nano-spheres, containing functionalized aromatic groups.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Agar-derived nitrogen-doped porous carbon as anode for construction of cost-effective lithium-ion batteries

Balancing cost and performance of porous carbon (PC) as anode for lithium-ion battery (LIBs) is the key to effectively promote commercial application. Herein, low-cost N-doped PC (NPC-Ts, T = 600, 750 and 900 °C) were facilely prepared in batches via one-pot pyrolysis of agar with different carbonization temperature. The NPC-750 with specific surface area of 2914 m²/g and N content of 2.84% exhibits an ultrahigh reversible capacity of 1019 mAh/g at 0.1 A/g after 100 cycles and 837 mAh/g at 1 A/g after 500 cycles. Remarkably, the resulting LIBs exhibit an ultrafast charge-discharge feature with a remarkable capacity of 281 mAh/g at 10 A/g and a superlong cycle life with a capacity retention of 87% after 5000 cycles at 10 A/g. Coupling with LiFePO₄ cathode, the fabricated lithium-ion full cells possess high capacity, excellent rate and cycling performances (125 mAh/g at 100 mA/g, capacity retention of 95%, after 220 cycles), highlighting the practicability of this NPC-750 as the anode materials.     

Electrochemical performance of LiVPO<Subscript>4</Subscript>F/C composite cathode prepared through amorphous vanadium phosphorus oxide intermediate

LiVPO₄F/C composites with better electrochemical performance were prepared by calcination of LiF and amorphous vanadium phosphorus oxide (VPO) intermediate synthesized by a sol–gel method using H₃PO₄, V₂O₅ and citric acid as raw materials. The properties of LiVPO₄F/C composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. The analysis of XRD patterns and Fourier transform infrared spectra (FTIR) reveal that VPO intermediate prepared by sol–gel method is amorphous and VPO₄ may exist in VPO intermediate. The compositions of LiVPO₄F/C composites are related to the calcination temperature for preparation of amorphous VPO/C intermediate and LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C consists of a single crystal phase of LiVPO₄F. The electrochemical tests show that LiVPO₄F/C composite prepared by VPO/C synthesized at 700°C exhibits higher discharge capacity and excellent cycle performance. This LiVPO₄F/C composite displays discharge capacity of 133 mAh g⁻¹ at 0.5 C (78 mA g⁻¹) and remains capacity retention of 96.8% after 30 cycles, even at a high rate of 5 C, the composite exhibits high discharge capacity of 115 mAh g⁻¹ and capacity retention of 97% after 100 cycles.     

Facile fabrication of porous NiO films for lithium-ion batteries with high reversibility and rate capability

We report the high-rate capability and good cyclability of three-dimension nanoporous NiO films as the anodes of lithium-ion batteries. The NiO films are fabricated by immersing foam nickel substrates in an 80 °C aqueous solution containing ammonia and potassium peroxydisulfate, and subsequent heat treatment at 500 °C. At a rate of 1.0 C, the film electrodes maintain a capacity of 560 mAh g⁻¹ as well as capacity retention of 97% after 100 discharge/charge cycles. When the current density is increased to 14C, 42% of the capacity can be retained. Owing to the ease of large-scale fabrication and superior electrochemical performance, these NiO films will be promising anodes for high-energy-density lithium-ion batteries.     

Ether-based electrolyte enabled Na/FeS2 rechargeable batteries

We demonstrate for the first time that by simply substituting ether-based electrolyte (1.0 M NaCF₃SO₃ in diglyme) for the commonly used carbonate-based electrolyte, the cyclability of FeS₂ towards sodium storage can be significantly improved. A sodiation capacity over 600 mAh/g and a discharge energy density higher than 750 Wh/kg are obtained for FeS₂ at 20 mA/g. When tested at 60 mA/g, FeS₂ presents a sodiation capacity of 530 mAh/g and retains 450 mAh/g after 100 cycles, much better than the cycling performance of Na/FeS₂ tested in carbonate-based electrolyte.     

Hierarchically structured MoO2/dopamine-derived carbon spheres as intercalation electrodes for lithium-ion batteries

A hydrogen peroxide initiated sol-gel process involving molybdenum transformation in the presence of dopamine (Dopa) hydrochloride excess produced the metastable precipitate composed of polydopamine (PDopa) spheres coated with Dopa preintercalated molybdenum oxide, (Dopa)_xMoO_y@PDopa. The hydrothermal treatment (HT) of the (Dopa)_xMoO_y@PDopa precursor resulted in the simultaneous carbonization of Dopa and molybdenum reduction generating MoO₂ nanoplatelets distributed and confined on the surface of the Dopa-derived carbon matrix (HT-MoO₂/C). The consecutive annealing (An) of the HT-MoO₂/C sample at 600 °C under Ar atmosphere led to the formation of MoO₂ with increased Mo oxidation state and improved structural stability (AnHT-MoO₂/C). Annealing had also further facilitated interaction between the molybdenum-derived and Dopa-derived components resulting in the modification of the carbon matrix confirmed by Raman spectroscopy. Morphology of both materials is best described as Dopa-derived carbon spheres decorated with MoO₂ nanoplatelets. These integrated metal oxide and carbon structures were tested as electrodes for lithium-ion batteries in the potential window that corresponds to the intercalation mechanism of charge storage. The AnHT-MoO₂/C electrode showed enhanced electrochemical activity, with an initial specific discharge capacity of 260 mAh/g and capacity retention of 67% after 50 cycles, compared to the HT-MoO₂/C electrode which exhibited an initial specific discharge capacity of 235 mAh g^?1 and capacity retention of 47% after 50 cycles. The rate capability experiments revealed that the capacity of 93 mAh/g and 120 mAh/g was delivered by the HT-MoO₂/C and AnHT-MoO₂/C electrodes, respectively, when the current density was increased to 100 mA/g. The improved specific capacity, electrochemical stability, and rate capability achieved after annealing were attributed to higher crystallinity of MoO₂, increased oxidation state of Mo, and formation of the tighter MoO₂/carbon contact accompanied by the annealing assisted interaction between MoO₂ and Dopa-derived carbon.     

Continuous supercritical hydrothermal synthesis: lithium secondary ion battery applications

Nanosized lithium iron phosphate (LiFePO₄) and transition metal oxide (MO, where M is Cu, Ni, Mn, Co, and Fe) particles are synthesized continuously in supercritical water at 25?C30?MPa and 400??C under various conditions for active material application in lithium secondary ion batteries. The properties of the nanoparticles, including crystallinity, particle size, surface area, and electrochemical performance, are characterized in detail. The discharge capacity of LiFePO₄ was enhanced up to 140?mAh/g using a simple carbon coating method. The LiFePO₄ particles prepared using supercritical hydrothermal synthesis (SHS) deliver the reversible and stable capacity at a current density of 0.1?C rate during ten cycles. The initial discharge capacity of the MO is in the range of 800?C1,100?mAh/g, values much higher than that of graphite. However, rapid capacity fading is observed after the first few cycles. The continuous SHS can be a promising method to produce nanosized cathode and anode materials.     

Li0.93[Li0.21Co0.28Mn0.51]O2 nanoparticles for lithium battery cathode material made by cationic exchange from K-birnessite

Li_0.93[Li_0.21Co_0.28Mn _0.51]O₂ nanoparticles with an R-3m space group is hydrothermally prepared from Co_0.35Mn_0.65O₂ obtained from an ion-exchange reaction with K-birnessite K_0.32MnO₂ at 200 °C. Even at a hydrothermal reaction temperature of 150 °C, the spinel (Fd3m) phase is dominant, and a layered phase became dominant by combining an increase in the temperature to 200 °C with an increase in lithium concentration. The as-prepared cathode particle has plate-like hexagonal morphology with a size of 100 nm and thickness of 20 nm. The first discharge capacity of the cathode is 258 mAh/g with an irreversible capacity ratio of 22%, and the capacity retention after 30 cycles is 95% without developing a plateau at ∼3 V. Capacity retention of the cathode discharge is 84% at 4C rate (=1000 mA/g) and shows full capacity recovery when decreasing the C rate to 0.1 C.     

Drastically enhanced cycle life of Co-B alloy electrode by 8-hydroxyquinoline at elevated temperature

The effect 8-hydroxyquinoline (8-HQ) additive in electrolyte on the cyclic stability of Co-B alloy electrode was investigated at elevated temperature (55 °C). Charge–discharge measurements show that 8-HQ can drastically enhance the cycle life of Co-B alloy electrode. Specifically, in the electrolyte containing 0.028 M 8-HQ additive, the discharge capacity of Co-B alloy electrode after 100 cycles are still up to 385.8 mAh/g at 55 °C. However, for the electrode in 8-HQ-free electrolyte, its discharge capacity is sharply decreased to only 138.5 mAh/g after 100 cycles. ICP-OES, XRD and ATR/FT-IR measurements were used to clarify the reason of the improvement in the cyclic stability. These results show that beneficial effect of 8-HQ on cycle life of Co-B alloy electrode can be attributed to the formation of insoluble complex (8-HQ)₂Co(II)·2H₂O protective layer that can suppress the dissolution of Co(OH)₂ into electrolyte at elevated temperature.     

High-performance Na1.25V3O8 nanosheets for aqueous zinc-ion battery by electrochemical induced de-sodium at high voltage

Aqueous rechargeable zinc-ion batteries (ARZIBs) are expected to replace organic electrolyte batteries owing to its low price, safe and environmentally friendly characteristics. Herein, we fabricated vanadium-based Na_1.25V₃O₈ nanosheets as a cathode material for ARZIBs, which present a high performance by electrochemical de-sodium at high voltage to form Na₂V₆O₁₆ phase in the first cycle: high capacity of 390 mAh/g at 0.1 A/g, high rate performance (162 mAh/g at 10 A/g) and superior cycle stability (179 mAh/g with a high capacity retention of 88.2% of the maximum capacity after 2000 cycles). In addition, the cell exhibits a high energy density of 416.9 Wh/kg at 143.6 W/kg, suggesting great potential of the as-prepared Na_1.25V₃O₈ nanosheets for ARZIBs     

Rational design of Prussian blue analogue-derived manganese-iron oxides-based hybrids as high-performance Li-ion-battery anodes

The unique components and architecture of Prussian blue analogous (PBAs) offer great potential for the construction of various functional nanostructures. Herein, we reported the preparation of a series of Mn–Fe oxides-based hybrids using Mn–Fe PBA as a template and an organic carbon source by calcination. The study focuses on revealing the interaction between the microstructure and electrochemical performance of the products obtained at different calcination temperatures. Notably, the as-derived porous Fe–Fe_0.33Mn_0.67O/C nanocubes (i.e., M600) exhibited the best rate capability and cycle life compared with other samples (～890 mAh/g at 0.1 A/g, 626.8 mAh/g after 1000 cycles at 1.0 A/g with a 99% capacity retention). These can be attributed to the fact that the porous structure provides shorter Li⁺ diffusion path and promotes the penetration of electrolyte. Besides, the N?doped C formed by the carbonization of organic ligands can buffer the volume change and prevent the aggregation of Fe_0.33Mn_0.67O nanoparticles during the discharge/charge cycles. Moreover, the presence of metallic Fe enhances the conductivity and the electrochemical activity, which accelerates the electrochemical reactions. Therefore, reasonable design of microstructure and compositions of functional nanocomposites is the key to obtain ideal electrochemical properties.     

Effect of fullerene coating on silicon thin film anodes for lithium rechargeable batteries

To improve the electrochemical performances of Si thin film anodes for lithium rechargeable batteries, fullerene thin films are prepared by plasma-assisted evaporation methods to be used as coating materials. Analyses via Raman and X-ray photoelectron spectroscopy indicate that amorphous polymeric films originated from fullerene are formed on the surface of the silicon thin film. The electrochemical performance of these fullerene-coated silicon thin film as an anode material for rechargeable lithium batteries has been investigated by cyclic voltammetry, charge/discharge tests, and electrochemical impedance spectroscopy. The fullerene-coated Si thin films demonstrated a high specific capacity of above 3,000 mAh g⁻¹ as well as good capacity retention for 40 cycles. In comparison with bare silicon anodes, the fullerene-coated silicon thin film showed superior and stable cycle performance which can be attributed to the fullerene coating layer which enhances the Li-ion kinetic property at the electrode/electrolyte interface.