Electrospun LiCoPO4@C Composite Nanofibers As High-Voltage Cathode Materials for Lithium-Ion Batteries
Authors: Berikbaikyzy Samal , Bakenov Zhumabay , Belgibayeva Ayaulym 
Published: December 2024

Lithium-ion batteries (LIBs) have revolutionized modern technology with their high energy density allowing longer use in portable electronic devices. Their long cycle life and negligible memory effect further enhance their appeal [1]. However, there are challenges such as lower power density, safety risks including thermal runaway, and an aging effect requiring further development [2].

Lithium cobalt phosphate (LCP) offers a possibility of high energy density, owing to its high working potential of 4.8 V vs. Li/Li+ and moderate theoretical capacity of 167 mAh g-1. Furthermore, good thermal stability of LCP can further contribute to the efficient use of LIBs [3]. Despite these advantages, the electrochemical performance of LCP is affected by low ionic and electrical conductivities which cause poor cycle life and rate capability [4]. These limitations could also be accompanied by electrolyte selection and its decomposition at high voltages during delithiation-lithiation of LCP [2] . Thus, this research aims to improve the overall characterizations of LCP@C cathode materials by synthesizing continuous, free-standing nanofibers using the environmentally friendly electrospinning method and implementing nanosize structure enhancing ionic diffusivity [4]. The effect of pre-oxidation temperatures on electrochemical performance of LCP@C cathode materials is studied as well.

The electrospinning solution was prepared as previously reported [5] but with a difference of adding a stoichiometric amount of lithium nitrate and electrospun at specified electrospinning parameters. The fibers underwent heat treatment at 700 ℃ in a nitrogen environment after being dried at 150 ℃ and pre-oxidized at various temperatures, indicated in samples’ names. By using scanning electron microscopy (SEM, Crossbeam500, Zeiss) and X-ray diffraction (XRD, Miniflex, Rigaku), the crystal structure and morphology of nanofibers were investigated, respectively.

Using CR2032 coin-type cells built in a glove box with 99.9995% pure Ar gas, the electrochemical performance was tested. The cells were equipped with Li chips as reference electrodes, polypropylene separators, ~50 μL of an electrolyte solution comprising 1 M LiPF6 in a mixture of ethylene carbonate and dimethyl carbonate (EC:DMC=1:1 vol.) solvents, and LCP@C composite nanofibers as free-standing cathodes with mass loading of ~2 mg cm-2. At a current density of 0.1 C, the cells were tested in the potential range of 3.5 – 5.3 V vs. Li/Li+.

Formation of LCP in the samples have been verified via XRD analysis given in Fig. 1 a, showing a similar pattern for all six samples pre-oxidized at 280-380 ℃. The peak around 22-23 ℃ corresponds to the presence of lithium phosphate for the LCP@C-280 sample. The SEM image in Fig. 1 b shows the formation of nanofibers with beads on materials, the average diameter of fibers is 280-330 nm.

Electrochemical performance of prepared LCP@C nanofibers will be presented at the conference.

Acknowledgements

This research was funded by the projects AP19675260 “Development of nanofibrous electrode materials for next-generation lithium-ion batteries”and AP13068219 “Development of multifunctional free-standing carbon composite nanofiber mats” from the Ministry of Education and Science of the Republic of Kazakhstan.

References

[1] Y. Chen et al., Journal of Energy Chemistry 59 (2021) 83-99. DOI:10.1016/j.jechem.2020.10.017

[2] J. Liu et al., Journal of Cleaner Production 423 (2023) 138678.DOI:10.1016/j.jclepro.2023.138678

[3] T. A. Hamdalla et al., Ceramics International 49 (2023) 1214–1219 DOI:10.1016/j.ceramint.2022.09.099.

[4] A. Belgibayeva et al., Electrochimica Acta 419 (2022) DOI:10.1016/j.electacta.2022.140400.

[5] A. Belgibayeva et al., ChemElectroChem. 9 (2022) DOI:10.1002/celc.202200458

Figure 1