Influence of Resorcinol to Sodium Carbonate Ratio on Carbon Xerogel Properties for Aluminium Ion Battery

Abstract

Carbon xerogels were synthesized using a soft-template route with resorcinol as the carbon source and sodium carbonate as the catalyst. The influence of the resorcinol to catalyst ratio in the range of 500-20,000 on pore structure, graphitic domains, and electronic conductivity of as-prepared carbon xerogels, as well as their performance in an aluminium ion battery (AIB), was investigated. After carbonization steps of the polymers up to 800 °C, all carbon samples exhibited similar specific volumes of micropores (0.7-0.8 cm³ g^-1), while samples obtained from mixtures with R/C ratios lower than 2000 led to carbon xerogels with significantly higher mesopore diameters up to 6 nm. The best results, in terms of specific surface (1000 m² g^-1), average pore size (6 nm) and reversible capacity in AIB cell (28 mAh g^-1 @ 0.1 A g^-1), were obtained with a carbon xerogel sample synthetized at a resorcinol to catalyst ratio of R/C = 500 (CXG₅₀₀). Though cyclic voltammograms of carbon xerogel samples did not exhibit any sharp peaks in the applied potential window, the presence of both oxidation and a quite wide reduction peak in CXG_500-2000 cyclic voltammograms indicated pseudocapacitance behaviour induced by diffusion-controlled intercalation/de-intercalation of AlCl₄^- ions into/from the carbon xerogel matrix. This was confirmed by shifting of the (002) peak towards lower 2θ angle values in the XRD pattern of the CXG₅₀₀ electrode after the charging step in AIB, whereas the contribution of pseudocapacitance, calculated from half-cell measurements, was limited to only 6% of overall capacitance.

Keywords: Raman; X-ray diffraction; aluminium-ion battery; carbon; conductivity; intercalation; pseudo-capacitance; resorcinol; soft-template; xerogel.

Figure A1

Long-term cycling of CXG₅₀₀ in AIB full-cell setup.

Figure A2

Scan-rate variation of cyclic voltammograms for CXG₅₀₀||Al (a) and natural graphite||Al (b).

Figure A3

Determination of b-values in CXG₅₀₀||Al at the anodic (a) and cathodic (b) CV scan and for natural graphite for intercalation peaks a_1–5 (c) and deintercalation peaks c_1–4 (d).

Figure A3

Determination of b-values in CXG₅₀₀||Al at the anodic (a) and cathodic (b) CV scan and for natural graphite for intercalation peaks a_1–5 (c) and deintercalation peaks c_1–4 (d).

Figure 1

As-prepared resorcinol-formaldehyde resins after drying step from high catalyst concentration (R/C = 50) on the left side to low concentration (R/C = 20,000) on the right side.

Figure 2

Characterisation of CXG by isotherms (a), pore size distribution with respect to V_sum (b), contribution of microporous and mesoporous pore volume and surface area (c) and repartition of relative mesopore and micropore volume (d).

Figure 3

XRD diffractogram of selected CXG and natural graphite (a). Stacking width L_A and stacking height L_C of graphene crystallites as a function of R/C ratio during CXG synthesis (b).

Figure 4

Raman spectra of selected CXG (a). Position of D and G-band as well as Γ_D- and Γ_G-band as a function of R/C value (b).

Figure 5

Conductivity and density values of CXG powders as a function of R/C ratio.

Figure 6

SEM images of CXG₅₀₀ (a), CXG₇₅₀ (b), CXG₁₀₀₀ (c), CXG₁₅₀₀ (d), CXG₂₀₀₀ (e), CXG₂₅₀₀ (f) and natural graphite powders (g) at 5 kV.

Figure 6

SEM images of CXG₅₀₀ (a), CXG₇₅₀ (b), CXG₁₀₀₀ (c), CXG₁₅₀₀ (d), CXG₂₀₀₀ (e), CXG₂₅₀₀ (f) and natural graphite powders (g) at 5 kV.

Figure 7

CVs of selected CXGs and natural graphite in 1:1.5 n(EmimCl):n(AlCl₃) electrolyte (a) and influence of average pore size on max. current density taken from CVs of selected CXG at 2.25V (b). Deconvoluted current contribution of non-diffusion limited (pseudo)capacitance and diffusion-limited Faradaic currents in CXG₅₀₀||Al (c) and in graphite||Al (d). “(pseudo)capacitance” designation comprises both EDLC and pseudocapacitance contribution.

Figure 7

CVs of selected CXGs and natural graphite in 1:1.5 n(EmimCl):n(AlCl₃) electrolyte (a) and influence of average pore size on max. current density taken from CVs of selected CXG at 2.25V (b). Deconvoluted current contribution of non-diffusion limited (pseudo)capacitance and diffusion-limited Faradaic currents in CXG₅₀₀||Al (c) and in graphite||Al (d). “(pseudo)capacitance” designation comprises both EDLC and pseudocapacitance contribution.

Figure 8

Charging/discharging experiments of CXG₅₀₀ (a), CXG₇₅₀ (b), CXG₁₀₀₀ (c), CXG₁₅₀₀ (d), CXG₂₅₀₀ (e) and natural graphite (f) in Swagelok-type straight-cells with tungsten as cathodic current collector and aluminium rod as anode in n(EMimCl):n(AlCl₃) 1:1.5 electrolyte.

Figure 9

Charging and discharging curves of AIBs equipped with CXG_500–2500 (a) and natural graphite for comparison (b).

Figure 10

Ex situ XRD analysis of pristine and fully charged natural graphite and CXG₅₀₀ electrodes. Peaks marked with (*) indicate position of (002) peak in both pristine electrodes. The peak marked with (∆) is assumed to be associated with the (002) peak shift due to intercalated species in CXG₅₀₀. Peaks indexed with (◊) are related to GIC-induced peaks in natural graphite sample.