Claims:CLAIMS:
I / We Claim:
1. A method of preparing one dimensional PbO nanofibers for lithium-ion batteries, comprising:
taking 1 g of Polyvinylpyrrolidone (PVP) powder in a first beaker and dispersing it in ethanol by stirring overnight to obtain a PVP solution;
taking 1 g of Lead acetate anhydrous powder (Pb(CH3COO)2) in a second beaker and dispersing it in dimethylformamide (DMF) and ethanol by stirring for 2 hours to obtain a lead acetate solution;
adding said lead acetate solution to said PVP solution and stirring overnight to obtain a homogeneous viscous PVP/PbAc solution;
injecting said homogeneous viscous PVP/PbAc solution into a 20mL glass syringe with a blunt-end needle;
applying a positive voltage of 20 kV with a distance of 15 cm between the needle end and a grounded foil collector drum and performing electrospinning to obtain composite PVP/PbAc nanofibers;
drying said composite PVP/PbAc nanofibers for 24 hours under vacuum at 80°C; and
subjecting said dried composite PVP/PbAc nanofibers to calcination at 550 °C for 3 hours to yield one dimensional PbO nanofibers (PbO NFs),
whereby said method yields lead monoxide (PbO) nanofibers (NFs) that possess high conductivity and low activation energy for applications in lithium-ion batteries as anode.
2. The method of preparing one dimensional PbO nanofibers for lithium-ion batteries as recited in claim 1, wherein said glass syringe with the blunt-end needle with an inner diameter of 0.4 mm is injected with viscous PVP/PbAc solution.
3. The method of preparing one dimensional PbO nanofibers for lithium-ion batteries as recited in claim 1, wherein said A4 size aluminium foil wrapped on the grounded foil collector drum serves as a counter electrode.
4. The method of preparing one dimensional PbO nanofibers for lithium-ion batteries as recited in claim 1, wherein constant feed rate of said homogeneous viscous PVP/PbAc solution of 0.4 ml/h is adjusted using a syringe pump and the rotation speed of the grounded foil collector drum is maintained at 150 rpm.
5. The method of preparing one dimensional PbO nanofibers for lithium-ion batteries as recited in claim 1, wherein said electrospinning is performed at room temperature with a relative humidity of 40-45%.
6. The method of preparing one dimensional PbO nanofibers for lithium-ion batteries as recited in claim 1, wherein said obtained PbO nanofibers (PbO NFs) are prepared as anode by combining 80 weight percentage of PbO nanofibers (PbO NFs), 10 weight percentage of polymer [Polyvinylidene fluoride (PVDF)] conductive binder, and 10 weight percentage of super-P carbon black conductive additives for electrode slurry preparation using N-methyl-2-pyrrolidone (NMP) solvent that is coated by copper foil and dried in a vacuum oven at 120 °C for 12 hours using doctor’s blade process and later pressed, followed by cutting it into a circular disk.
7. The method of preparing one dimensional PbO nanofibers for lithium-ion batteries as recited in claim 1, wherein said calcination is performed with a heating rate of 2 °C/min. , Description:DESCRIPTION:
Field of the invention:
The present disclosure generally relates to the technical field of anode materials, and in specific relates to a method of preparing one dimensional lead monoxide (PbO) nanofibers (NFs) that yields high conductivity and low activation energy for its applications in lithium-ion batteries as anode.
Background of the invention:
Global energy demand grew rapidly in the 21st century, and developments in energy supply including sources of renewable energy such as nuclear energy, fuel cells, and their environmental impacts are being focused in recent times. The energy demand is increasing day by day in an exponential manner and in future, this demand will be higher in comparison with the present day’s energy needs. Lithium-ion batteries (LIB) are one of the promising devices for the regulation of electronic gadgets due to their storage capacity for small mobile devices. Graphite is primarily used as a generic anode material in consumer LIBs applications because of its low price and ideal cycle properties.

The limited theoretical capacity hinders graphite use over the next decade. Researchers need to develop new materials for LIB anode with properties such as high specific power, high energizing, high longevity, longer life-cycles, and that are available at cheap cost, to meet future energy storage requirements. As the anode material dominates the electrochemical output of LIBs, attempts have been made to create new anode materials that could potentially replace graphite with exceptional electrochemical results.

Metal oxides, including NiO, Co3O4, SnO2, and CuO are considered suitable anode materials for the application, due to their superior specific capacity. But, due to high costs, their use as commercial anode materials is limited. To meet the growing energy demand of modern electronics, other cheaper lithium-storage materials such as lead-based materials can be made with suitable metallic components. However, the low retention rate, poor cycling stability, and short life cycle caused during alloying or dealloying by the substantial shift in the volume of lead-based materials indicate a lack of durability and reduced life span.

Electrospinning is an industrially flexible, very simple, reliable and easy processing of nanofibers for the processing of organic and inorganic nanofibers with long lengths, uniform diameters, good mechanical strength, various compositions, large surface area, high porosity, low production costs, and easy access, making it extremely useful among many available techniques. The diameter of nanofibers obtained using electrospinning typically ranges between tens of nanometers to a few micrometres. One of the main advantages of the electrospinning technique is its versatility of processing that aids to create fibers with multiple arrangements and morphological structures. The popularity of the electrospinning technique has allowed multiple technologies such as tissue engineering, regenerative medicine, and encapsulation of bioactive molecules, to emerge and evolve over the past decade.

In existing technology, PbO nanoparticles for lithium batteries are synthesized using hydrothermal process. The crystallographic structure of the powders obtained is β-PbO which is a suitable material for Li-ion anodes. The cyclic voltammetry of the PbO nanoparticles embodied two major peaks related to the formation of Li2O during the reduction of PbO to Pb and SEI layers. However, the hydrothermal method has many disadvantages such as relatively long production cycle, rigid temperature, and pressure conditions thereof.

Conventional processes of preparing PbO nanoparticles for anode applications are tedious and time-consuming. There is no simple method that yields nanomaterial of lead monoxide with superior properties required for applications as anode in batteries. There is no low-cost anode material for lithium-ion batteries. An anode material with less activation energy is needed with high conductivity for lithium ion batteries.

Therefore, there is a need for a method of preparing lead monoxide (PbO) nanomaterial that yields high conductivity and low activation energy for applications in lithium-ion batteries as anode. There is a need for a low-cost material for anodes in lithium-ion batteries. There is a need for an anode material for batteries with enhanced mobility of carriers at low cost. An anode material with a large surface area is required to provide an effective contact area for electrode or electrolyte and faster ion or electron diffusion.
Objectives of the invention:
The primary objective of the invention is to provide a method of preparing one dimensional lead monoxide (PbO) nanofibers (NFs) that yields high conductivity and low activation energy for its applications in lithium-ion batteries as anode.

Another objective of the invention is to utilize electrospinning and calcination to prepare lead monoxide (PbO) nanofibers (NFs) for its utilization as Li-ion battery anode material at low cost.

The other objective of the invention is to evaluate various properties of lead monoxide (PbO) nanofibers (NFs) using TG-DTA, XRD, BET surface area analyzer, FTIR, Raman, FE-SEM, TEM, and EDX techniques.

Yet another objective of the invention is to obtain lead monoxide (PbO) nanofibers (NFs) with high conductivity and low activation energy due to the 1-D nanostructural properties that aids to enhance the mobility of the carriers.

Further objective of the invention is to provide lead monoxide (PbO) nanofibers that possess high crystallinity, electrical conductivity, mesoporosity and fibrous structure with large surface area thereby providing an effective contact area for electrode or electrolyte and faster ion or electron diffusion.

The other objective of the invention is to provide lead monoxide (PbO) nanofibers that are ready to use, and exhibit excellent cycling performance compared to PbO nanoparticles and have potential use in low-power devices, such as mobile phone batteries.
Summary of the invention:
The present disclosure proposes PbO nanofibers for lithium-ion batteries and its preparation method thereof. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide a method of preparing one-dimensional lead monoxide (PbO) nanofibers (NFs) that yields high conductivity and low activation energy for its applications in lithium-ion batteries as anode.

According to an aspect, the invention provides a method of preparing one-dimensional PbO nanofibers for lithium-ion batteries. The method yields lead monoxide (PbO) nanofibers (NFs) that possess high conductivity and low activation energy for applications in lithium-ion batteries as an anode. The method includes the steps comprising of taking 1 g of Polyvinylpyrrolidone (PVP) powder in a first beaker and dispersing it in ethanol by stirring overnight to obtain a PVP solution. Then, 1 g of Lead acetate anhydrous powder (Pb(CH3COO)2) is taken in a second beaker and dispersed in dimethylformamide (DMF) and ethanol by stirring for 2 hours to obtain a lead acetate solution. Next, the lead acetate solution is added to the PVP solution and stirred overnight to obtain a homogeneous viscous PVP/PbAc solution.

Later, the homogeneous viscous PVP/PbAc solution is injected into a 20mL glass syringe with a blunt-end needle. In specific, the glass syringe with the blunt-end needle with an inner diameter of 0.4 mm is injected with viscous PVP/PbAc solution. The constant feed rate of the homogeneous viscous PVP/PbAc solution of 0.4 ml/h is adjusted using a syringe pump and the rotation speed of the grounded foil collector drum is maintained at 150 rpm. Then, a positive voltage of 20 kV is applied with a distance of 15 cm between the needle end and a grounded foil collector drum and electrospinning is performed to obtain composite PVP/PbAc nanofibers. The A4 size aluminium foil wrapped on the grounded foil collector drum serves as a counter electrode. In specific, the electrospinning is performed at room temperature with a relative humidity of 40-45%.

Next, composite PVP/PbAc nanofibers are dried for 24 hours under vacuum at 80°C. Later, the dried composite PVP/PbAc nanofibers are subjected to calcination at 550 °C for 3 hours to yield one-dimensional PbO nanofibers (PbO NFs). In specific, the calcination is performed with a heating rate of 2 °C/min.

The obtained PbO nanofibers (PbO NFs) are prepared as an anode by combining 80 weight percentage of PbO nanofibers (PbO NFs), 10 weight percentage of the polymer [Polyvinylidene fluoride (PVDF)] conductive binder, and 10 weight percentage of super-P carbon black conductive additives for electrode slurry preparation using N-methyl-2-pyrrolidone (NMP) solvent that is coated by copper foil and dried in a vacuum oven at 120 °C for 12 hours using doctor’s blade process and later pressed, and cut it into a circular disk.

Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.

FIG. 1 illustrates an exemplary method of preparing one-dimensional PbO nanofibers for lithium-ion batteries in accordance to an exemplary embodiment of the invention.

FIG. 2A illustrates TGA plots of as-spun (composite PVP/PbAc) Nanofibers and pure PVP nanofibers in accordance to an exemplary embodiment of the invention.

FIG. 2B illustrates the PVP/PbAc composite fibers sample in accordance to an exemplary embodiment of the invention.

FIG. 2C illustrates XRD patterns for PbO nanofibers along with standard JCPDS data in accordance to an exemplary embodiment of the invention.

FIG. 2D illustrates Raman spectrum of PbO nanofibers in accordance to an exemplary embodiment of the invention.

FIG. 3A illustrates nitrogen isothermic adsorption/desorption curves for 1-D PbO nanofibers at 77 K in accordance to an exemplary embodiment of the invention.

FIG. 3B illustrates pore size distribution of 1-D PbO nanofibers at 77 K in accordance to an exemplary embodiment of the invention.

FIG. 3C illustrates 1/[Q(P/Po-1)] vs. relative pressure (P/Po) plots 1-D PbO nanofibers at 77 K in accordance to an exemplary embodiment of the invention.

FIG. 4A illustrates as-spun PVP/PbAc fibrous mat in accordance to an exemplary embodiment of the invention.

FIG. 4B illustrates optical microscopic images of as-spun PVP/PbAc fibrous mat in accordance to an exemplary embodiment of the invention.

FIG. 5A to 5G illustrate FE-SEM, TEM, HR-TEM, SAED and EDX elemental mappings of Pb and O elements in PbO nanofibers in accordance to an exemplary embodiment of the invention.

FIG. 6A and 6B illustrate Nyquist [imaginary (-Z″) vs. real (Z′)] plots obtained at different temperatures for the PbO Nanofibers along with Inset of equivalent circuit of the PbO nanofibers in accordance to an exemplary embodiment of the invention.

FIG. 6C illustrates Log (σT) versus 1000/T plot of the PbO nanofibers in accordance to an exemplary embodiment of the invention.

FIG. 6D illustrates AC conductivity versus frequency plots obtained at different temperatures of the PbO nanofibers in accordance to an exemplary embodiment of the invention.

FIG. 7A illustrates Electrochemical impedance spectra of mesoporous 1-D PbO nanofibers along with equivalent circuit model in inset figure in accordance to an exemplary embodiment of the invention.

FIG. 7B illustrates CV curves for the first three cycles in accordance to an exemplary embodiment of the invention.

FIG. 7C illustrates discharge-charge curves of mesoporous 1-D PbO Nanofibers electrode at 1st, 2nd, and 50th cycles at a constant current density of 100 mA g−1 (0.1 C rate) in accordance to an exemplary embodiment of the invention.

FIG. 7D illustrates cycling performance and corresponding coulombic efficiency of PbO nanofibers electrodes at 0.1 C rate in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.

The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide a method of preparing one dimensional lead monoxide (PbO) nanofibers (NFs) that yields high conductivity and low activation energy for its applications in lithium-ion batteries as anode.

According to an exemplary embodiment of the invention, FIG. 1 refers to a method 100 of preparing one-dimensional PbO nanofibers for lithium-ion batteries. The method 100 yields lead monoxide (PbO) nanofibers (NFs) that possess high conductivity and low activation energy for applications in lithium-ion batteries as an anode. The method 100 includes the steps comprising of taking 1 g of Polyvinylpyrrolidone (PVP) powder in a first beaker and dispersing it in ethanol by stirring overnight to obtain a PVP solution at step 101. Then at step 102, 1 g of Lead acetate anhydrous powder (Pb(CH3COO)2) is taken in a second beaker and dispersed in dimethylformamide (DMF) and ethanol by stirring for 2 hours to obtain a lead acetate solution. Next at step 103, the lead acetate solution is added to the PVP solution and stirred overnight to obtain a homogeneous viscous PVP/PbAc solution.

Later at step 104, the homogeneous viscous PVP/PbAc solution is injected into a 20mL glass syringe with a blunt-end needle. In specific, the glass syringe with the blunt-end needle with an inner diameter of 0.4 mm is injected with viscous PVP/PbAc solution. The constant feed rate of the homogeneous viscous PVP/PbAc solution of 0.4 ml/h is adjusted using a syringe pump and the rotation speed of the grounded foil collector drum is maintained at 150 rpm.

Then at step 105, a positive voltage of 20 kV is applied with a distance of 15 cm between the needle end and a grounded foil collector drum and electrospinning is performed to obtain composite PVP/PbAc nanofibers. The A4 size aluminium foil wrapped on the grounded foil collector drum serves as a counter electrode. In specific, the electrospinning is performed at room temperature with a relative humidity of 40-45%.

Next at step 106, composite PVP/PbAc nanofibers are dried for 24 hours under vacuum at 80°C. Finally at step 107, the dried composite PVP/PbAc nanofibers are subjected to calcination at 550 °C for 3 hours to yield one-dimensional PbO nanofibers (PbO NFs). In specific, the calcination is performed with a heating rate of 2 °C/min.

The obtained PbO nanofibers (PbO NFs) are prepared as an anode by combining 80 weight percentage of PbO nanofibers (PbO NFs), 10 weight percentage of the polymer [Polyvinylidene fluoride (PVDF)] conductive binder, and 10 weight percentage of super-P carbon black conductive additives for electrode slurry preparation using N-methyl-2-pyrrolidone (NMP) solvent that is coated by copper foil and dried in a vacuum oven at 120 °C for 12 hours using doctor’s blade process.

The dried copper foil is later pressed and cut it into a circular disk. Lithium metallic foil is used as an auxiliary electrode and a Whatman glass microfiber (GF/D) paper filter is used as a separator. The PbO nanofibers are directly used as an anode material in the half coin-type CR-2032 lithium cells and their electrochemical tests. An electrochemical workstation is used for the measurement of galvanostatic charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectrum (EIS).

According to another exemplary embodiment of the invention, FIG. 2A refers to TGA plots of as-spun (composite PVP/PbAc) nanofibers and pure PVP nanofibers. The decomposition of pure PVP nanofibers takes place in two steps while for as-spun nanofibers it is in three steps. For PVP, the initial weight loss is about ~9% under 83°C that corresponds to the evaporation of solvents such as water and ethanol present in the PVP nanofibers. The relatively flat portion in the temperature range 85°C to 383°C of PVP indicates the slow intramolecular decomposition of PVP while the rapid weight loss started at 385°C corresponds to the intramolecular decomposition and evaporation of PVP.

The flat portion after 480°C corresponds to the complete elimination of PVP. In the case of PVP/PbAc as-spun fibers, the initial weight loss of ~18% in the temperature range 60°C to 130°C could be ascribed to the evaporation of solvents and partial decomposition (melt) of PbAc with the dehydration of crystal water from PbAc. Additional weight loss in the temperature range 260°C to 370°C could be attributed to the complete dehydration and decomposition of PbAc with formation of PbO.

The intramolecular decomposition of PVP is well accompanied during this temperature. When the temperature exceeds around 450°C, no more weight loss occurs, indicating whole removal of the organic species. After 450°C, there is no change in weight loss, indicating the creation of pure inorganic oxides. This thermal analysis shows the temperature of the synthesis above 450°C is needed to produce high-quality PbO nanofibers.

According to another exemplary embodiment of the invention, FIG. 2B refers to PVP/PbAc composite fibers sample. The PVP/PbAc composite fibers sample exhibited almost peak free XRD pattern, except one peak around at 2θ = 24°, that confirms the formation of the amorphous phase of PVP/PbAc composite fibers.

According to another exemplary embodiment of the invention, FIG. 2C refers to XRD patterns for PbO nanofibers along with standard JCPDS data. The XRD peaks are compared with standard JCPDS data and the formation of pure orthorhombic lead oxide (PbO) is observed. During refinement, the value of the crystallite size and the lattice parameters of the PbO nanofibers are determined as ~68 nm, and a = 5.4428 Å, b = 4.7278 Å, and c = 5.848 Å respectively. Thus, the formulation of the nanocrystalline orthorhombic PbO phase is successfully synthesized using electrospinning technique based on XRD findings.

According to another exemplary embodiment of the invention, FIG. 2D refers to the PbO nanofibers Raman spectrum. The orthorhombic PbO nanofibers sample consists of twelve active Raman optical vibration modes (i.e., 4 Ag + 4 B1g + 2 B2g + 2 B3g). Four strong Raman peaks of 71, 88, 144 and 288 cm-1 are observed. The highest peak, centred at 144 cm-1 is ascribed to the Ag mode. The remaining low Raman intensity peaks observed at 56, 98, 166, 221, 221, 248, 344, and 388 cm-1 are ascribed to mode B3g, B2g, Ag, B3g, B2g, Ag, B1g and Ag, respectively. Theoretically predicted difference in frequency between the peaks at 216 and 217 cm-1 (orthorhombic PbO nanofibers) is more important but it is not easy to distinguish relatively low intensity and typical peak width of about 1 cm-1 separately. The phonon frequency mode acquired experimentally is observed at 221 cm-1.

According to another exemplary embodiment of the invention, FIG. 3A to 3C refer to nitrogen isothermic adsorption/desorption curves, pore size distribution, and 1/[Q(P/Po-1)] versus relative pressure (P/Po) plots for 1-D PbO nanofibers at 77 K. N2 isothermic adsorption-desorption behaviours are referred to the IUPAC standards, and the isothermic pattern is very well observed to fit type-IV isothermic activity with H3 hysteresis, suggesting that the nanofibers obtained may be mesoporous form material.

The electrospinning technique is found to be effective in the preparation of the larger surface area and smaller particle sizes of mesoporous PbO nanofibers. The specific surface area, pore size, and volume of the pores are 61.23 m2g-1, 9 nm, and 0.2493 cm3g-1, respectively. PbO nanofibers have a specific surface area of 61.20 m2g-1, which is 10 times greater than the literature values reported.

According to another exemplary embodiment of the invention, FIG. 4A refers to as-spun PVP/PbAc nanofibers. Optical microscopic images are used to observe the formation and size of PVP/PbAc electrospun composite nanofiber mats for initial examination. The optical microscopic result in FIG. 4B depicts that the nanofibers have relatively uniform size.

According to another exemplary embodiment of the invention, FIG. 5A refers to FE-SEM micrographs of the PbO nanofibers. The diameter of the PbO fibers ranges between 100 to 150 nm. The FE-SEM micrographs clearly show the rough surface PbO nanofibers. This effect may potentially have a beneficial impact by using the nanofibers as a catalyst as opposed to the smooth nanofibers, the rough surface nanofibers have a large surface area.

FIG. 5B to FIG. 5G refer to TEM, HR-TEM, SAED and EDX elemental mappings of Pb and O elements in PbO nanofibers. The TEM micrograph showed that the diameter of PbO nanofiber is found to be 150 nm that is strongly consistent with the FE-SEM micrographs. From FIG. 5C it is observed that the interplanar lattice (311) spacing of the plane is found to be 0.306 nm, which is in good agreement with the JCPDS (01-076-1796) orthorhombic PbO phase. From FIG. 5D, the results of the SAED pattern support the formation of orthorhombic polycrystalline PbO nanofibers. From FIG. 5E, FIG. 5F and FIG 5G, it is clearly observed that the EDX mapping images exhibit the Pb and O elements, which agrees well with the designed composition of PbO nanofibers. The TEM, HR-TEM, SAED micrographs, and EDX spectrum analysis verify pure crystalline 1-D PbO nanofibers.

FIG. 6A and FIG. 6B refer to Nyquist (imaginary (-Zʹʹ) vs. real (Zʹ)) plots obtained at different temperatures for the PbO nanofibers pellet sample. It is observed that the Nyquist plots of PbO nanofibers depict the single semicircle for all temperatures in the measured frequency range. Further, it is also observed that the radius of the semicircle decreases with increasing temperature, which indicates the decrease in resistance with the increase of temperature which in turn, increases the conductivity of PbO nanofibers.

The measured impedance data of PbO nanofibers is analyzed using winfit software. The obtained resistance (R) and electrical behavior, in terms of equivalent circuit, shown in the inset of FIG. 6A. The formation of single semicircle corresponds to the parallel combination of constant phase element (CPE) and resistance of the PbO nanofibers. The obtained total resistance from the impedance plot is used to calculate the electrical conductivity (σ) of the PbO nanofibers sample, by using the following equation:
σ=1t\RA
Where t is the thickness of the PbO nanofibers sample and A is the area of the sample. The observed electrical conductivity of the PbO nanofibers samples is found to be 5.40 x 10-6 S cm-1 and 3.38 x 10-5 S cm-1 respectively at 298 K and 423 K.

The obtained electrical conductivity of the PbO nanofibers sample at different temperatures are fitted to the following Arrhenius equation using the least square fit:
σt=σ0 exp⁡(-Ea/T)
Where, σ is the conductivity, T is the absolute temperature, σ0 is the temperature independent conductivity, K is the Boltzmann constant and Ea is the activation energy.

According to another exemplary embodiment of the invention, FIG. 6C refers to Log (σT) versus 1000/T plot of the PbO nanofibers. All the symbols are measured data and straight line indicates the fitted data. The activation energy (Ea) is calculated from the slope of the log (σT) versus 1000/T plot in the temperature range 298K to 423K. The calculated activation energy (Ea) for the migration of the charge carriers in the PbO nanofibers sample is found to be 0.24 eV.

According to another exemplary embodiment of the invention, FIG. 6C refers to σac vs. log (ω) plots obtained at different temperatures ranging from 298 K to 423 K for PbO nanofibers sample. The frequency dependence of conductivity plots showed two distinct regions within the measured frequency window such as the low frequency plateau region and the high frequency dispersion region.

The plateau region corresponds to frequency independent conductivity σ(0) or dc conductivity (σdc) and is evaluated by extrapolating the plateau region to the zero frequency (Y-axis). The frequency independent conductivity may be attributed to the long range transport of free charge carriers with the applied field in the PbO nanofibers. The observed a.c. conductivity in the high frequency dispersion region is fitted to the following Jonscher’s universal power law (JUPL) using a non-linear regression analysis.
σ(ω) = σ(0) + Aωs
Where σ (ω) is the ac conductivity, σ (0) is the zero frequency limit of σ (ω), A is a constant, and s is the power law exponent (0 < s < 1). From FIG. 6D, it is observed that the frequency at which the dispersion region deviated from the plateau is defined as the hopping frequency (ωp), where, the relaxation effect starts. An increase of a.c. conductivity at high frequency in the PbO nanofibers is due to hopping of electrons between adjacent sites, results in local displacement of charge carriers in the direction of the applied frequency.

FIG. 7A displays the electrochemical impedance spectra (EIS) of LIBs produced by the mesoporous 1-D PbO nanofibers electrode (inset figure shows the equivalent circuit model) during the 1st and 50th cycle charging processes. From FIG. 7A, Nyquist (real Z′ vs. imaginary Z′′) plot shapes for the 1st and 50th cycle of mesoporous PbO nanofibers electrode are the same. From the plots it is observed that there is a consisted of a small high-frequency intercept, a high to medium frequency semicircle, and an inclined straight line at low frequencies.

A fitting equivalent circuit is inserted in FIG. 8B. The impedance of interception is approximately the same, corresponding to the resistance of the manufactured cell (RΩ). Depressed semicircle intermediate frequency connected to the electrical/electrolyte interface's charging transfer resistance (Rct), and double-layer capacitance (Cdl). The inclined straight line at low-frequency corresponds to the Warburg impedance (Zw). From FIG. 7A, it can be seen that the Li-ion battery developed using the 1-D PbO nanofibers 1st cycle has a lower resistance (30.36 Ω), which means that the charging impedance is much lower than the Li-ion battery produced using the 1-D PbO anode 100th cycle (225.3 Ω). The 100th cycle reduced Rct of 1-D PbO nanofibers is believed to have been attributed to the number of cycling processes.

FIG. 7B refers to cyclic voltammogram (CV) curves of the Li-ion battery developed as an anode using the 1-D PbO nanofibers. The Li/PbO nanofiber cells are conducted between 0.01 to 3 V, CV studies at a scan rate of 0.1 mV s-1 over the first 3 cycles. The initial CV curve shows the 10 reduction peaks in the lithiation cycle at 1.59, 1.39, 1.34, 1.14, 1.05, 0.52, 0.47 0.31, 0.25, 0.18 V and the six oxidation peaks in the 0.35, 0.45, 0.51, 0.64, 1.26, 1.34 V delithiation cycle.

The reduction peaks at 1.59 to 1.05 V mainly attribute to the formation of SEI film. The strong reduction peak at 1.35 V is due to the reaction of Li to PbO (i.e., the formation of Pb and Li2O). This peak disappears in subsequent cycles, indicating the irreversibility of the reaction. The reduction peak ranges at 0.52 to 0.18 V corresponds to the formation of specific LixPb alloys (0 < x < 4.5). The two oxidation peaks are assigned to the dealloy process using LixPb alloys. The CV curves exhibit high reproducibility after the initial cycle. The first cycle reaction process can be summed up as follows:
PbO + 2Li+ + 2e- → Pb + Li2O
Pb + xLi+ +xe- ↔ LixPb (0 ≤ x ≤ 4.5)
FIG. 7C represents the discharge/charge anode curves at 1st, 2nd, and 50th cycles of PbO NFs electrode at 0.1 C rate in the voltage range of 0.0 to 3 V. The 1st discharge capacity of the mesoporous 1-D PbO NFs anode is found to be 1271 mAh g-1, which is much higher than the PbO nanoparticles. It is also more than the theoretical capacity of PbO (768 mAh g-1). The excess capacity of 503 mAh g-1 could be due to the formation of a Li2O and a solid electrolyte interface (SEI) at the electrode and electrolyte interface due to electrolyte reduction during initial discharge process. In the 2nd cycle, the discharge and charge specific capacity of the samples are 575 mAh g-1 and 458 mAh g-1, respectively.

From the initial cycle to the 2nd cycle, the phenomenon of capacity loss is also remarkable due to irreversible reactions. In the 50th cycle, the reversible discharge capacity of the PbO NFs electrode remained at 372 mAh g-1. These preliminary data illustrate that the cycle performance of PbO nanofibers electrode is useful as a anode material for Li-ion batteries.

FIG. 7D displays the cycling performance and coulombic efficiency of electrospun mesoporous 1-D PbO nanofibers at a 0.1 C rate. Apparently, the capacity decay rapidly in the first three to five cycles. This behaviour may be caused by the complicated side-reactions and irreversible reactions [45]. Then the decay speed gradually lowers until the capacity becoming relatively stable. The reversible discharge capacity maintains at 372 mAh g-1 after 50 cycles with a stable coulombic efficiency of around 98%.

The capacity retention of the PbO nanofibers is better than that of commercial carbonaceous materials and some PbO samples. The superior lithium storage properties of the PbO nanofibers electrode may be related to the unique continuous fibrous morphologies, nanostructured architectures, porous structures, and large specific surface area, which provide an easily Li+ diffusion path and promote electron transfer. As a result, the newly developed mesoporous 1-D electrospun PbO NFs anode using the electrospinning and calcination processes can be a better anode material for the LIB applications.

Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, a method of preparing one dimensional lead monoxide (PbO) nanofibers (NFs) is disclosed that yields high conductivity and low activation energy for its applications in lithium-ion batteries as anode. The method utilizes electrospinning and calcination to prepare lead monoxide (PbO) nanofibers (NFs) for its utilization as Li-ion battery anode material at low cost.

The present disclosure evaluates various properties of lead monoxide (PbO) nanofibers (NFs) using TG-DTA, XRD, BET surface area analyzer, FTIR, Raman, FE-SEM, TEM, and EDX techniques. The proposed method aids to obtain lead monoxide (PbO) nanofibers (NFs) with high conductivity and low activation energy due to the 1-D nanostructural properties that aids to enhance the mobility of the carriers.

The obtained lead monoxide (PbO) nanofibers possess high crystallinity, electrical conductivity, mesoporosity and fibrous structure with large surface area thereby providing an effective contact area for electrode or electrolyte and faster ion or electron diffusion. The lead monoxide (PbO) nanofibers are ready to use, and exhibit excellent cycling performance compared to PbO nanoparticles and have potential use in low-power devices, such as mobile phone batteries.

It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.