The performance of Sodium-Ion Battery, SIB, with NaFePO4 cathode prepared from local iron sand was investigated. The NaFePO4 was prepared through electrochemical sodiation to FePO4 layer on aluminium substrate. NaFePO4 prepared from local iron sand (from NTB, Indonesia) is named as NFP_A. The result is compared to the performance of SIB with NaFePO4 cathode prepared from a commercial FePO4, which is named as NFP_B. The SIB was fabricated in a split cell test type and a pouch type. Battery performance was measured by Cyclic Voltammetry (CV) analysis, Galvanostatic Charge-Discharge (GCD) testing, and Electrochemical Impedance Spectroscopy (EIS) measurements. CV analysis found that sodium intercalation and de-intercalation curve in NFP_A is similar to the CV curve of NFP_B. The reduction peak presents at -2.98 V and -2.99 V for NFP_A and NFP_B, respectively. Those peaks represent Na+ intercalation into FePO4 layer. The oxidation peaks, that represent deintercalation from NaFePO4 appears at 3.31 and 3.96 V. Split cell SIB with NFP_A as cathode provides 100 cycles under 1 C and 3 C current drawn. Meanwhile, the pouch type only provides 50 cycles before the capacity loss under 1 C current drawn. Each type has 100 % Coulombic efficiency indicates that all of the charged-ion can be completely discharged.
In this research, a cyclic voltammetry (CV) method was applied to intercalate Na + into an FePO4/Al substrate to produce NaFePO4/Al as a potential cathode material. The sodiation was conducted directly to FePO4 instead of applying delithiation to LiFePO4 followed by sodiation, as was done in previous research. CV was conducted within a potential window of 2.0-4.0 V using a scan rate of 0.05 mVs -1 . The result was compared to LiFePO4/Al treated with a similar method. The various scan rate was then applied to understand its effect on the electrochemical activity recorded in the voltammogram and its impedance profile. The results show that the CV product of FePO4/Al (NFP(A)) was crystallized in an orthorhombic olivine NaFePO4, as a result of Le Bail refinement. Orthorhombic Na0.7FePO4, trigonal FePO4, and monoclinic FePO4 were presented as secondary phases. Meanwhile, the CV product of LiFePO4/Al (NFP(B)) was also crystallized in olivine NaFePO4 and possessed secondary phases similar to NFP(A) with an additional Fe2O3 phase. NFP(A) showed two significant peaks at 2.442 V and 3.534 V, confirming sodiation/de-sodiation and Fe 3+ /Fe 2+ activity, respectively. Meanwhile, NFP(B) showed two peaks at 3.183 V and 3.04 V, corresponding to de-lithiation and sodiation, respectively. The Nyquist plots of both materials show a similar profile, with the impedance value of NFP(A) being lower than that of NFP(B). This confirms that the CV treatment of FePO4/Al is more facile than the treatment of the LiFePO4 layer, while also producing a cathode with higher electrical conductivity. Scan rate reduction to 0.04 mVs -1 produced a much lower impedance value, confirming higher electrical conductivity.
Research to prepare NaFePO4 cathode material from iron sand was conducted. The iron sand consists of ilmenite FeTiO3 and hematite Fe2O3. A caustic fusion method used to precipitate iron as Fe(OH)3 and it increased Fe content up to 94.71 %. Phosphate precipitation successfully produced trigonal FePO4 and monoclinic FePO4 comply with ICSD#412736 and ICSD#281079. The prepared-FePO4 was then used as a precursor for Na insertion by applying cyclic voltammetry mode within 2.0 – 4.0 V with 0.05 mVs-1 of the scan rate. It produced orthorhombic olivine NaFePO4 and a secondary phase of orthorhombic Na0.7FePO4. Impedance analysis at 20 Hz – 5 MHz found that the material provided a semicircle at 100 Hz peak point, indicating electrode-bulk interface with a resistance value of 1735W, comparable to the electrical conductivity of 5.36 x 10-6 Scm-1. Even though the conductivity value is quite lower than NaFePO4 prepared from a commercial FePO4 that has been conducted in our previous research, however the electrical conductivity still reliable for cathode.
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