Graphite-Phosphate Composites: Structure and Voltammetric Investigations

Abstract

The utilization of lithium-ion batteries (LIBs) is increasing sharply with the increasing use of mobile phones, laptops, tablets, and electric vehicles worldwide. Technologies are required for the recycling and recovery of spent LIBs. In the context of the circular economy, it is urgent to search for new methods to recycle waste graphite that comes from the retired electrode of LIBs. The conversion of waste graphite into other products, such as new electrodes, in the field of energy devices is attractive because it reduces resource waste and processing costs, as well as preventing environmental pollution. In this paper, new electrode materials were prepared using waste anode graphite originating from a spent mobile phone battery with an xBT·0.1C₁₂H₂₂O₁₁·(0.9-x)(NH₄)₂HPO₄ composition, where x = 0-50 weight% BT from the anodic active mass of the spent phone battery (labeled as BT), using the melt quenching method. Analysis of the diffractograms shows the graphite crystalline phase with a hexagonal structure in all prepared samples. The particle sizes decrease by adding a higher BT amount in the composites. The average band gap is 1.32 eV (±0.3 eV). A higher disorder degree in the host network is the main factor responsible for lower band gap values. The prepared composites were tested as electrodes in an LIB or a fuel cell, achieving an excellent electrochemical performance. The voltammetric studies indicate that doping with 50% BT is the most suitable for applications as electrodes in LIBs and fuel cells.

Keywords: cyclic voltammetry; graphite composites; impedance; spent mobile phone battery; structure.

Figure 1

(a) Spent phone battery; (b) punctured phone battery; (c,d) the disassembled components of the spent phone battery; (e) images of the obtained samples in the xBT·0.1C₁₂H₂₂O₁₁·(0.9-x) (NH₄)₂HPO₄ composition, where x = 0–50 weight% BT.

Figure 2

X-ray diffractograms of the (a) spent anodic powder (noted with BT) and (NH₄)₂HPO₄ glassy; (b–d) prepared samples in the xBT·0.1C₁₂H₂₂O₁₁·(0.9-x)(NH₄)₂HPO₄ composition, where x = 0–50 weight% BT.

Figure 3

FTIR spectra of the prepared composites in the region between (a,b) 450 and 4000 cm⁻¹; (c) 400 and 1500 cm⁻¹.

Figure 4

EPR spectra of the spent BT and of the graphite–phosphate composites. (a) Spent BT, x = 15 and 20% BT; (b) x = 30 and 50% BT; (c) x = 15–50% BT; (d) x = 15% BT.

Figure 5

(a) The UV-Vis data of the spent BT powder and prepared samples; (b) the compositional evolution of optical gap energy, E_g, for direct transitions with n = 1/2 of the prepared samples.

Figure 6

Cyclic voltammograms of the electrode materials with xBT·0.1C₁₂H₂₂O₁₁·(0.9-x) (NH₄)₂HPO₄ chemical formula, where (a) x = 20, 30, and 50 weight% BT (BT—cathodic active mass of the spent phone battery) in 0.15 M Li₂CO₃ and 0.1 M Na₂CO₃ mix solution and (b) x = 30 and 50 weight% BT in 1 M KOH solution.

Figure 7

Cyclic voltammograms of the electrode materials with x = 50 weight% BT in (a) a 1 M KOH electrolyte solution at varied scan rates and (b) in KOH (1 M concentration) and Li₂CO₃/Na₂CO₃ electrolyte solutions.

Figure 8

(a) Cyclic voltammograms scanned after two cycles for the prepared electrode materials in KOH and Li₂CO₃/Na₂CO₃ electrolyte solutions; (b) Nyquist plot of the complex impedance of the electrode material with x = 50% BT obtained in the KOH electrolyte solution.