Effect of Electrolyte Concentration on the Electrochemical Performance of Spray Deposited LiFePO4

LiFePO4 is a common electrode cathode material that still needs some improvements regarding its electronic conductivity and the synthesis process in order to be easily scalable. In this work, a simple, multiple-pass deposition technique was utilized in which the spray-gun was moved across the substrate creating a “wet film”, in which—after thermal annealing at very mild temperatures (i.e., 65 °C)—a LiFePO4 cathode was formed on graphite. The growth of the LiFePO4 layer was confirmed via X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The layer was thick, consisting of agglomerated non-uniform flake-like particles with an average diameter of 1.5 to 3 μm. The cathode was tested in different LiOH concentrations of 0.5 M, 1 M, and 2 M, indicating an quasi-rectangular and nearly symmetric shape ascribed to non-faradaic charging processes, with the highest ion transfer for 2 M LiOH (i.e., 6.2 × 10−9 cm2/cm). Nevertheless, the 1 M aqueous LiOH electrolyte presented both satisfactory ion storage and stability. In particular, the diffusion coefficient was estimated to be 5.46 × 10−9 cm2/s, with 12 mAh/g and a 99% capacity retention rate after 100 cycles.


Introduction
Aqueous metal-ion (Li, Zn, Na, K, Mg, Ca, etc.) batteries and ammonium-ion batteries have exhibited extraordinary qualities for applications in energy storage, owing to their quality of security and the different electrode materials that can be utilized [1,2]. Lithium iron phosphate (LiFePO 4 ) is an excellent cathode material for Li-ion batteries (LIBs) because it is extremely safe, thermally stable, and low cost [1,2]. Nevertheless, the electronic conductivity is poor, and the diffusion coefficient is slow, which limit the development for high power devices [3]. Hence, there is a lot of space for research to explore ways to improve the material's performance. There is an increasing interest in the optimization of the synthesis route (doping modification, morphological regulation, nanosized particles) [4][5][6], the coating with electron-conducting layer and orientation control [7], and computational research on the understanding of the ionic dynamic properties of LiFePO 4 [8]. However, there is not sufficient information on the investigation of LiFePO 4 thin films as cathodes. Thin film manufacturing processes have significant advantages because the cost of scalable roll-to-roll processes is reduced. In addition, the thickness of the cathode can be altered to a value such that the deficient electronic conductivity does not affect the electrochemical performance of the electrode [9].

Spray Deposited LiFePO 4
The solution was prepared by dissolving the correct amount of LiOH, iron sulphate (FeSO 4 ), and phosphoric acid (H 3 PO 4 ) in distilled water in a stoichiometric ratio of 1:1:1. Following this procedure, LiOH was initially mixed with FeSO 4 , with the final addition of H 3 PO 4 . The concentrations of Li + , Fe 2+ , and PO 4 3+ were all 0.01 M and the volume of the final solution reached 60 mL. Then, 10 mL of the prepared solution were placed in the spray gun for the LiFePO 4 deposition on the graphite substrate ( Figure 1). The graphite substrate, with a size of 1 × 1 cm 2 , was placed on a hot plate at 65 • C. The distance between the spray gun and the substrate was kept at 13 cm, moving the spray gun (to the right and left) across the substrate for the deposition to take place. For each spray, 10 s was allowed to elapse for the solution to dry, and the subsequent spray was continued. After the completion of the spraying process, the LiFePO 4 /graphite remained on the hotplate for 15 more minutes.

Basic Characterization
X-ray diffraction (XRD) analysis was performed to study the structure of LiFePO 4 using SmartLab ® SE (by Rigaku Europe SE-Hugenottenallee 167 Neu-Isenburg 63263, Germany) for processing parameters: power 46 kV, 50 mA, and speed time 8 min. Confocal micro-Raman measurements at room temperature were acquired with a system of Thermo Fisher Scientific model DXRxi. We used a 532 nm laser as the excitation beam with 20 mW power, exposure time 0.1 s, and objective lens long distance ×10. In addition, a monochromated Al-Kα source was utilized for X-ray photoelectron spectroscopy (XPS) measurements in FlexMod (SPECS-SPECS Surface Nano Analysis GmbH Voltastrasse 5, 13355 Berlin, Germany) with X-ray source XR-50 and 15 kV/200 W. Finally, field-emission scanning electron microscopy (FE-SEM) was used to analyze the morphology of the as-grown LiFePO 4 in JSM-IT700HR InTouchScope™ Field Emission SEM (by Thermo Fisher Scientific-Neuhofstrasse 11, 4153 Reinach TechCenter, 4153 Basel, Switzerland) for processing parameters: 20 kV power, 10 µm width.

Basic Characterization
X-ray diffraction (XRD) analysis was performed to study the structure of LiFePO4 using SmartLab ® SE (by Rigaku Europe SE-Hugenottenallee 167 Neu-Isenburg 63263, Germany) for processing parameters: power 46 kV, 50 mA, and speed time 8 min. Confocal micro-Raman measurements at room temperature were acquired with a system of Thermo Fisher Scientific model DXRxi. We used a 532 nm laser as the excitation beam with 20 mW power, exposure time 0.1 s, and objective lens long distance ×10. In addition, a monochromated Al-Kα source was utilized for X-ray photoelectron spectroscopy (XPS) measurements in FlexMod (SPECS-SPECS Surface Nano Analysis GmbH Voltastrasse 5, 13355 Berlin / Germany) with X-ray source XR-50 and 15 kV/200 W. Finally, field-emission scanning electron microscopy (FE-SEM) was used to analyze the morphology of the asgrown LiFePO4 in JSM-IT700HR InTouchScope™ Field Emission SEM (by Thermo Fisher Scientific-Neuhofstrasse 11, 4153 Reinach TechCenter, 4153 Basel, Switzerland) for processing parameters: 20 kV power, 10 μm width.

Electrochemical Evaluation of LiFePO4
For the electrochemical evaluation of LiFePO4 film cathodes, a three-electrode electrochemical cell was utilized [31,32]. The working electrode was the LiFePO4 film on graphite, the counter electrode was the graphite, and the reference electrode was Ag/AgCl. The measurements were performed in 0.5 M, 1 M, and 2 M aqueous solutions of LiOH with a scan rate of 50 mV/s and potential range of −0.7 V to +0.7 V. Measurements were also carried out at different scan rates of 10,20,30,40,50, and 100 mV/s. Finally, galvanostatic charge/discharge tests of LiFePO4 were performed at specific current 1.2 mA and ambient temperature (25 ± 1 °C). The electrochemical measurements took place in Autolab PGSTAT101 by Metrohm AG.

Electrochemical Evaluation of LiFePO 4
For the electrochemical evaluation of LiFePO 4 film cathodes, a three-electrode electrochemical cell was utilized [31,32]. The working electrode was the LiFePO 4 film on graphite, the counter electrode was the graphite, and the reference electrode was Ag/AgCl. The measurements were performed in 0.5 M, 1 M, and 2 M aqueous solutions of LiOH with a scan rate of 50 mV/s and potential range of −0.7 V to +0.7 V. Measurements were also carried out at different scan rates of 10, 20, 30, 40, 50, and 100 mV/s. Finally, galvanostatic charge/discharge tests of LiFePO 4 were performed at specific current 1.2 mA and ambient temperature (25 ± 1 • C). The electrochemical measurements took place in Autolab PGSTAT101 by Metrohm AG.  [33], in contrast with the strong signals from graphite (i.e., at 26.6 • and 54.5 • corresponding to (002) and (004) Miller indices) [34]. This behavior is due to the background intensities caused by the scattering from the substrate. Figure 2b shows the Raman spectra of the graphite substrate and LiFePO 4 film on graphite. The graphite spectrum is highly ordered, since it shows one in-plane vibration of the graphite lattice (G band) at 1575 cm −1 and a disorder band caused by the graphite edges at 1355 cm −1 [35]. Regarding the LiFePO 4 [36,37], two peaks can be identified at 1005 cm −1 and 1092 cm −1 , indicating the non-distorted PO 4 3− tetrahedral in the pristine LiFePO 4 . The mode at 425 cm −1 is assigned to O-P-O bending internal to the PO 4 3− anion. Finally, the mode at approximately 215 cm −1 is due to Fe-O vibrations.

Structure and Morphology Evaluation
Raman spectra of the graphite substrate and LiFePO4 film on graphite. The graphite trum is highly ordered, since it shows one in-plane vibration of the graphite latti band) at 1575 cm −1 and a disorder band caused by the graphite edges at 1355 cm −1 Regarding the LiFePO4 [36,37], two peaks can be identified at 1005 cm −1 and 1092 indicating the non-distorted PO4 3-tetrahedral in the pristine LiFePO4. The mode a cm −1 is assigned to O-P-O bending internal to the PO4 3-anion. Finally, the mode at ap imately 215 cm −1 is due to Fe-O vibrations.  Figure 3a shows the O 1s spectrum with two deconvoluted peaks at 531.5 eV 534.1 eV, attributed to oxygen atoms of the PO4 3-phosphate groups in LiFePO4 [38] oxygenated species adsorbed on the electrode surface deriving possibly from electr degradation [39], respectively. In P 2p spectrum (Figure 3b), two peaks are observ 132.3 eV and 133.4 eV, which are fitted to 2p3/2 and 2p1/2 components, respectively, d PO4 3-phosphate group indicating that this is the only phosphorus environment [40,4 1s spectrum (Figure 3c) shows one deconvoluted peak at 54.4 eV assigned to LiFePO Finally, the Fe 2p spectrum (Figure 3d) shows two peaks at 710.5 eV and 722.4 eV, w correspond to 2p3/2 and 2p1/2 for Fe 3+ [43]. There is one additional peak at 714.7 eV, w is characteristic of Fe 2+ with a weaker signal than Fe 3+ [42,44]. The presence of this imp may be due to the air exposure of the LiFePO4 material. All the above analysis, inclu XRD and Raman spectroscopy, confirm the presence of LiFePO4.  Figure 3a shows the O 1s spectrum with two deconvoluted peaks at 531.5 eV and 534.1 eV, attributed to oxygen atoms of the PO 4 3− phosphate groups in LiFePO 4 [38], and oxygenated species adsorbed on the electrode surface deriving possibly from electrolyte degradation [39], respectively. In P 2p spectrum (Figure 3b), two peaks are observed at 132.3 eV and 133.4 eV, which are fitted to 2p 3/2 and 2p 1/2 components, respectively, due to PO 4 3− phosphate group indicating that this is the only phosphorus environment [40,41]. Li 1s spectrum (Figure 3c) shows one deconvoluted peak at 54.4 eV assigned to LiFePO 4 [42]. Finally, the Fe 2p spectrum (Figure 3d) shows two peaks at 710.5 eV and 722.4 eV, which correspond to 2p 3/2 and 2p 1/2 for Fe 3+ [43]. There is one additional peak at 714.7 eV, which is characteristic of Fe 2+ with a weaker signal than Fe 3+ [42,44]. The presence of this impurity may be due to the air exposure of the LiFePO 4 material. All the above analysis, including XRD and Raman spectroscopy, confirm the presence of LiFePO 4 . The surface morphology of the LiFePO4 film grown on graphite is presented in Figure  3e. Figure 3e indicates a thick LiFePO4 film consisting of FePO4 flake-like particles with large size distribution (200 nm to 1 μm) observed [44]. A similar microstructure was also indicated for LiFePO4 prepared by a high-energy balling system [45] and chemical fabrication [46]. This type of morphology is expected to positively affect the electrochemical performance of the material under investigation because of the high contact area between the electrolyte and the cathode favoring the Li + diffusion. ticles with large size distribution (200 nm to 1 µm) observed [44]. A similar microstructure was also indicated for LiFePO 4 prepared by a high-energy balling system [45] and chemical fabrication [46]. This type of morphology is expected to positively affect the electrochemical performance of the material under investigation because of the high contact area between the electrolyte and the cathode favoring the Li + diffusion.

Electrochemical Analysis
In order to find the appropriate electrolyte concentration, the cyclic voltammetry (CV) curves were evaluated in 0.5 M, 1 M, and 2 M LiOH electrolytes (Figure 4a-c). The curves exhibit an almost rectangular shape, with two inconspicuous peaks in the redox processes (i.e., at approximately −0.5 V (cathode) and +0.3 V (anode)) indicating a non-faradaic charging process [47]. This process is based on the formation of a double layer at the electrode-electrolyte interface during the adsorption of Li + on LiFePO 4 film surface, as proposed in Equation (1) [47][48][49].
Nanomaterials 2023, 13, x FOR PEER REVIEW 6 of 13 In that case, the charge is mainly stored in the electrolyte and the electrolyte concentration is therefore expected to affect the cathode's performance [50]. The effect of LiOH concentration was studied, keeping the scan rate (i.e., 50 mV/s) and the potential window (i.e., −0.7 V to +0.7 V) constant for different scan numbers. In aqueous electrolytes with high salt concentration (2 M), the ion transfer is larger, resulting in higher specific current In that case, the charge is mainly stored in the electrolyte and the electrolyte concentration is therefore expected to affect the cathode's performance [50]. The effect of LiOH concentration was studied, keeping the scan rate (i.e., 50 mV/s) and the potential window (i.e., −0.7 V to +0.7 V) constant for different scan numbers. In aqueous electrolytes with high salt concentration (2 M), the ion transfer is larger, resulting in higher specific current as confirmed in Figure 4c. The ionic conductivity of LiOH for different concentrations is illustrated in Figure 3f, indicating that the enhanced electrochemical performance in 2 M LiOH is attributed to the high conductivity [51]. However, the stability of the cathode in highly concentrated LiOH electrolyte is poor after 100 scans, as one can observe from Figure 4c, which is also confirmed from the peeling of the sample in the electrochemical cell. In order to substantiate this performance, the specific capacity for each scan number was calculated from the cyclic voltammograms using Equation (2) [52] where Idv is the area of the CV curve, m is the mass of the active material in g, and v is the scan rate in V/s. In addition, the percentage change of specific capacity was estimated from Equation (3) where final is the specific capacity at 100 scans and initial is the respective value for the first scan.
The % change was found to be 16% (0.5 M LiOH), 11% (1 M LiOH), and 45% (2 M LiOH), verifying the enhanced stability of LiFePO 4 film tested in 1 M LiOH aqueous electrolyte. The ion mobility reduction with time under strong alkaline conditions is not in agreement with the results reported by Luo et al., who suggest that LiFePO 4 can be used over a range from 7 to 14 in aqueous solutions [53]. In that perspective, we could consider for future work the pH adjustment, the elimination of O 2 (placing the electrochemical cell in a glove box), and the coating (e.g., TiO 2 ) on the top of LiFePO 4 as a protective layer.
The performance of the LiFePO 4 film was also studied for scan rates of 10, 20, 30, 40, 50, and 100 mV/s in the different LiOH electrolyte concentrations (Figure 4d-f). All curves indicate the almost rectangular shape. In all cases, the specific current increases with the scan rate and the shape of the curves remains unchanged, demonstrating an excellent behavior for the LiFePO 4 film electrode. Figure 4g-i present the variation of specific capacity as estimated from Equation (2), with scan rate for the different electrolyte concentration investigated showing a decreasing trend for higher scan rates. This is due to the fact that the fast scan rates do not give sufficient time to the ions to intercalate into the LiFePO 4 film, resulting in lower specific capacities [54][55][56].
Based on Randles-Sevcik Equations (4) and (5) [55] I p = D 1/2 2.72 × 10 5 n 3/2 ACν 1/2 (4) where I p is the peak current in A, n is the number of electrons involved in the process, A is the area of the cathode in cm 2 , D is the diffusion coefficient in cm 2 /s, c is the concentration in mol cm −3 , v is the scan rate in V s −1 , and a is the slope as obtained in Figure 5 (left). To estimate the diffusion coefficient of the sample, the plot of the peak current as a function with the square root of the scan rate (υ 1/2 ) ( Figure 5 (right)) is initially obtained for the determination of the slope in each LiOH concentration. Following this procedure, the values are substituted on Equation (5) for the calculation of the diffusion coefficient. The highest value was 6.2 × 10 −9 cm 2 /s for the 2 M LiOH, which can be attributed to the highest ionic conductivity facilitating electron transfer within the cathode material and contributing to its overall enhanced performance [57,58]. Based on Table 1, one can also realize that it is one of the highest values reported in the literature, possibly due to the appropriate combination of electrode-electrolyte characteristics. Since LiOH is an electrolyte that has not been studied extensively for LiFePO 4 , it is worth investigating it further through the careful addition of other salts, such as Li 2 SO 4 [59], acting as conductive additives to optimize its conductivity.  The power law model can be used to estimate the charge storage mechanism. The peak current and the scan rate follow the power law as shown in Equations (6) and (7) [56] i = av b (6) log(i) = blog(v) + log(a) (7) Figure 5 (right) presents the variation of log (peak current) as a function with log(scan rate) and the fitted lines of LiFePO4 studied in 1 M and 2 M LiOH aqueous electrolyte. The data obtained from the 0.5 M electrolyte were not further studied due to the general low performance. The slope of the fitted line is the b-value. If it is equal to 0.5, the process is diffusion-controlled, while for the case of 1.0, the surface-induced capacitive process is valid [60][61][62]. In this work, the b-value was estimated to be 0.67 for both cases, which is very close to 1.0, exhibiting a domination of non-faradaic process (i.e., Li + adsorption on the surface of LiFePO4 film). Figure 6 presents the galvanostatic charge/discharge tests in the absolute potential range between −0.7 V to +0.7 V (vs. Ag/AgCl) using graphite as a counter electrode in 0.5 M, 1 M, and 2 M LiOH aqueous electrolytes. The highest specific capacity of the cathode studied in 2 M LiOH is expected, as discussed above, due to the higher conductivity of the electrolyte. One can observe plateaus during the discharging process, which may be

Cathode Diffusion Coefficient (cm 2 /s) Aqueous Electrolytes
LiFePO 4 /C (gel-combustion synthesis) [59] 0.8 × 10 −14 Saturated LiNO 3 LiFePO 4 (commercial powder) [60] 2.020 × 10 −9 Saturated LiNO 3 LiFePO 4 (in situ synthesis technique) [61] 1.5 × 10 −11 1 M Li 2 SO 4 LiFePO 4 /C (spraying drying process) [62] 1 The power law model can be used to estimate the charge storage mechanism. The peak current and the scan rate follow the power law as shown in Equations (6) and (7) [56] i = av b (6) log(i) = blog(v) + log(a) (7) Figure 5 (right) presents the variation of log (peak current) as a function with log(scan rate) and the fitted lines of LiFePO 4 studied in 1 M and 2 M LiOH aqueous electrolyte. The data obtained from the 0.5 M electrolyte were not further studied due to the general low performance. The slope of the fitted line is the b-value. If it is equal to 0.5, the process is diffusion-controlled, while for the case of 1.0, the surface-induced capacitive process is valid [60][61][62]. In this work, the b-value was estimated to be 0.67 for both cases, which is very close to 1.0, exhibiting a domination of non-faradaic process (i.e., Li + adsorption on the surface of LiFePO 4 film). Figure 6 presents the galvanostatic charge/discharge tests in the absolute potential range between −0.7 V to +0.7 V (vs. Ag/AgCl) using graphite as a counter electrode in 0.5 M, 1 M, and 2 M LiOH aqueous electrolytes. The highest specific capacity of the cathode studied in 2 M LiOH is expected, as discussed above, due to the higher conductivity of the electrolyte. One can observe plateaus during the discharging process, which may be due to the electrochemical properties of the cathode rising between a combination of Li + intercalation/deintercalation into the LiFePO 4 and the adsorption on the cathode surface as supported from power law. The cathode evaluated in 1 M LiOH aqueous electrolyte presented a specific capacity of 12 mAh/g with a capacity retention rate of 99% after 100 cycles, as estimated from the difference between the specific capacity at 100 scans and the first scan divided by the specific capacity at the first scan. The curves after 100 cycles are not included since they coincide with those of the first scan. Nanomaterials 2023, 13, x FOR PEER REVIEW 9 of 13 due to the electrochemical properties of the cathode rising between a combination of Li + intercalation/deintercalation into the LiFePO4 and the adsorption on the cathode surface as supported from power law. The cathode evaluated in 1 M LiOH aqueous electrolyte presented a specific capacity of 12 mAh/g with a capacity retention rate of 99% after 100 cycles, as estimated from the difference between the specific capacity at 100 scans and the first scan divided by the specific capacity at the first scan. The curves after 100 cycles are not included since they coincide with those of the first scan.
(a) (b) (c) Additionally, in Figure 6, a FE-SEM of spray deposited LiFePO4 film on graphite utilizing 10 mL spraying solution after cycling is shown. It presents the flake-like behavior, along with particle agglomerations and some cracks [63,64]. This is probably due to the volume changes taking place during the cycling process.
Regarding the Raman spectra of LiFePO4 after cycling, there are FePO4 Raman modes, which are similar to LiFePO4. However, delithiation of LiFePO4 or lithiation of FePO4 leads to changes in both peaks' amplitude and position [34]. Specifically, the G, D bands peaks are in lower wavenumbers (i.e., 1346 cm −1 , 1588 cm −1 ) as those presented in Figure 2. There are three peaks at 946 cm −1 , 1025 cm −1 , 1061 cm −1 corresponding to asymmetric stretching of PO4 3-, which appears due to the formation of FePO4 after the delithiation process. The lower peaks at 164 cm −1 and 387 cm −1 indicate the Fe-O and O-P-O bonds, as before cycling. From the above results it is confirmed that lithium ions insert in LiFePO4 during the lithiation process and that FePO4 is the second phase that is present on the delithiation from LiFePO4. The extraction of lithium ion from LiFePO4 to charge the cathode is presented as reaction (8), and the insertion of lithium into FePO4 on discharge as reaction (9) The specific capacity of the cathode reported in this work is higher than the solidstate reaction process [54] and hydrothermal growth [60], while it is lower (one order of magnitude) than the direct recovery of scrapped LiFePO4 [4], the commercial powder [48], the mechanochemical activation of LiFePO4 [59], along with sol-gel [63] and spray-drying of LiFePO4/C [62] (Table 2). Overall, the growth methods utilized for the deposition of LiFePO4 are not practically feasible on a large scale for commercial applications. In that Additionally, in Figure 6, a FE-SEM of spray deposited LiFePO 4 film on graphite utilizing 10 mL spraying solution after cycling is shown. It presents the flake-like behavior, along with particle agglomerations and some cracks [63,64]. This is probably due to the volume changes taking place during the cycling process.
Regarding the Raman spectra of LiFePO 4 after cycling, there are FePO 4 Raman modes, which are similar to LiFePO 4 . However, delithiation of LiFePO 4 or lithiation of FePO 4 leads to changes in both peaks' amplitude and position [34]. Specifically, the G, D bands peaks are in lower wavenumbers (i.e., 1346 cm −1 , 1588 cm −1 ) as those presented in Figure 2. There are three peaks at 946 cm −1 , 1025 cm −1 , 1061 cm −1 corresponding to asymmetric stretching of PO 4 3− , which appears due to the formation of FePO 4 after the delithiation process. The lower peaks at 164 cm −1 and 387 cm −1 indicate the Fe-O and O-P-O bonds, as before cycling. From the above results it is confirmed that lithium ions insert in LiFePO 4 during the lithiation process and that FePO 4 is the second phase that is present on the delithiation from LiFePO 4 . The extraction of lithium ion from LiFePO 4 to charge the cathode is presented as reaction (8), and the insertion of lithium into FePO 4 on discharge as reaction (9) [65,66].
The specific capacity of the cathode reported in this work is higher than the solidstate reaction process [54] and hydrothermal growth [60], while it is lower (one order of magnitude) than the direct recovery of scrapped LiFePO 4 [4], the commercial powder [48], the mechanochemical activation of LiFePO 4 [59], along with sol-gel [63] and spray-drying of LiFePO 4 /C [62] (Table 2). Overall, the growth methods utilized for the deposition of LiFePO 4 are not practically feasible on a large scale for commercial applications. In that perspective, the combination of liquid-based chemistry with spray-coating can result in high quality films at a low temperature of approximately 65 • C, as indicated from the cathode characterization. In particular, it combines the advantages of low cost and low-complexity environments (i.e., in ambient air, low temperature processing, binder-and surfactant-free materials). Nevertheless, there is space for future work, including the involvement of a conductive material as a suspension in the spraying solution of LiFePO 4 to enhance the cathode's conductivity and as a consequence the overall electrochemical performance. Last but not least, restrictions for scaling-up results can be overcome through computational fluid dynamics (CFD) studies of the spray-gun process as a prospective work. Theoretical predictions of the lab-scale experimental process will be directly compared with experimental measurements to validate the developed computational model. Upon its validation, the model will be applicable for experimental set-ups and conditions corresponding to the scaled-up process.

Conclusions
A simple, multiple-pass deposition technique was utilized after thermal annealing at very mild temperatures (i.e., 65 • C) for the growth of a LiFePO 4 layer on graphite as a cathode. The growth of the LiFePO 4 layer was successfully confirmed via XRD, Raman spectroscopy, and XPS. When the cathode was tested in different LiOH concentrations, the highest electrolyte concentration resulted in an enhanced electrochemical performance due to its high conductivity, with, however, poor stability strengthening the importance of 1 M LiOH. The behavior of the LiFePO 4 film was evaluated for different scan rates ranging from 10 mV/s to 100 mV/s, showing an excellent performance of the cathode with an almost rectangular shape of the CV curves and an increasing specific current with the scan rate. The specific capacity decreased with increasing scan rate, demonstrating that fast scan rates do not give sufficient time for the ions to intercalate into the LiFePO 4 film, resulting in lower specific capacities. Overall, the cathode electrode studied in an aqueous solution of 1 M LiOH showed a specific capacity of 12 mAh/g with a capacity retention rate of 99% after 100 cycles and a diffusion coefficient of 5.46 × 10 −9 cm 2 /s. This work gives a good basis and promising results for the future, focusing on the increase in the specific capacity of the cathode through pH adjustment (i.e., electrolyte solution), coating of a protective layer on the top of LiFePO 4 , and a controlled environment for the electrochemical evaluation to avoid the changes that may occur to the electrolytes, such as the possible conversion of LiOH to Li 2 CO 3 . From that perspective, further cycles need to be carried out along with structural/morphological analysis to understand the Li + intercalation mechanisms.