The Conversion of Li 2 SnO 3 Li-Ion Hybrid Supercapacitors from Pastes Containing LiCl-SnCl 2 Liquid Precursors Using an Atmospheric-Pressure Plasma Jet

: We fabricate lithium tin-based oxide Li 2 SnO 3 on carbon cloth from a gel-state precursor containing LiCl and SnCl 2 · 2H 2 O using a nitrogen atmospheric-pressure plasma jet (APPJ). APPJ treatment provides both a high-temperature environment for the conversion of precursor into Li 2 SnO 3 and nitrogen plasma reactive species for electrode surface modification. Here, the best electrochemical performance for the Li 2 SnO 3 Li-ion hybrid supercapacitors (Li–HSCs) is achieved with 480 s of APPJ processing. The areal capacity of the 480 s APPJ-processed Li 2 SnO 3 Li–HSCs reached 46.113 mC/cm 2 . The results indicate that APPJ is an effective tool for the rapid conversion processing of Li 2 SnO 3 electrodes for Li–HSCs.


Introduction
As electrical energy storage (EES) systems progress, the focus of numerous researchers has turned to supercapacitors (SCs) and lithium-ion batteries (LIBs).These emerging technologies are driving a revolution across various domains, from small-scale portable electronics to hybrid electric vehicles [1][2][3][4].Although LIBs have high energy density, their power density is relatively low [5,6].By contrast, SCs have a much higher power density and a faster charging rate than LIBs, and thus can perfectly compensate for the shortcomings of LIBs [7,8].Therefore, Li-ion hybrid SCs (Li-HSCs), which combine the advantages of SCs and LIBs, have become attractive for use in next-generation EES devices [9,10].
The energy storage mechanism of supercapacitors (SCs) can be categorized as electrical double-layer capacitance (EDLC) and pseudocapacitance (PC).EDLC is mainly related to accumulating charges on the chemical reactive surface, and PC is related to reversible redox reactions [11][12][13].Li-HSCs need high-performance materials, and a high concentration of Li + ions can offer intercalation and deintercalation charge storage mechanisms [14,15].Various Li-containing materials, such as Li 2 SnO 3 , LiMn 2 O 4 , Li 2 MnO 3 , Li 2 MnSiO 4 , and Li 5 FeO 4 , are being rapidly developed for Li-HSCs because they are abundant, cost-effective, less polluting, and less harmful to humans [16][17][18].Among these, Li 2 SnO 3 has proven to be a promising material with great electrochemical performance.Li 2 SnO 3 crystalizes in a monoclinic layered structure with space group C2/c and consists of eight molecules per unit cell.Patterson and difference Fourier maps have been used to determine the atomic positions of all Li + , Sn 4+ and O 2-in a structure [19].Because Li 2 SnO 3 is sintered in high-temperature conditions, the medium-temperature APPJ technology can be applied.
Unlike low-pressure plasma (LPP), the atmospheric-pressure plasma jet (APPJ) can operate at regular atmospheric pressures without requiring vacuum systems.It contains highly reactive species and a high energy density, delivering rapid and cost-effective processing technology.The typical issues with APPJ technology, such as continuous arcing, instability, and high breakdown voltage problems, have been resolved, and the technology has become a suitable industrial processing method [20][21][22].Practical applications, such as material surface modification, sterilization and bacteria inactivation, rapid annealing, and the rapid processing of transition metal oxides, widely employ APPJs in various fields [23,24].Material processing utilizing medium-temperature atmospheric-pressure plasma jets (APPJs) relies on the combined impact of heat and reactive species from the plasma.This synergy results in the generation of practical medium-to-high temperatures within the plasma, along with diverse charge densities [25].Among the many kinds of gases available, nitrogen is abundant, economical, and environmentally friendly.In previous studies, nitrogen APP has been proven to be highly reactive to carbonaceous materials.When carbonaceous materials were treated by nitrogen APPJ in our experiment, the screenprinted pastes containing ethyl cellulose on carbon cloth were completely removed within ~90 s, and the Li 2 SnO 3 crystal was sintered within about 300 s.These results can be attributed to the synergetic effect of reactive plasma species and heat.In the present study, rapidly APPJ-processed Li 2 SnO 3 Li-HSCs are investigated.

Fabrication of Li-HSCs
Figure 1a shows the fabrication process of the Li 2 SnO 3 electrode.The LiCl-SnCl 2 pastes were applied to the carbon cloth (1.5 cm × 2 cm) through screen printing, repeated three times, and subsequently dried in an oven at 100 • C for 10 min.The screen-printed electrodes were then processed using a nitrogen APPJ.The nitrogen flow rate of the APPJ was 46 slm.The APPJ processing times were 0, 5, 30, 90, 180, 300, and 480 s for converting the LiCl-SnCl 2 precursor into Li 2 SnO 3 and for burning out the excess binders on the electrodes.The electrodes were then used for the Li-HSCs.Figure 1b shows the carbon cloth temperature, measured using a K-type thermocouple.The temperature rapidly increased to 500 • C and then gradually increased to 620 • C after the APPJ was turned on.Other detailed APPJ operation parameters were described in a previous study [26].Lastly, with a three-electrode configuration in a 1-M Li 2 SO 4 liquid electrolyte, the Li 2 SnO 3 Li-HSCs were used as the working electrode, and the reference and counter electrodes were represented by Ag/AgCl and Pt electrodes, respectively [27].

Characterizations of Li2SnO3 and Li-HSCs
A Sindetake Model 100SB goniometer measured the water contact angle of Li2SnO3 onto carbon cloth.The electrode surface morphology was inspected using a JEOL JSM-7800 F Prime scanning electron microscope (SEM) (Tokyo, Japan), equipped with the capacity to perform energy-dispersive X-ray spectroscopy (EDS).The crystallinity of Li2SnO3 was examined using a Bruker D2 Phaser X-ray diffractometer (Billerica, MA, USA) with a Cu-Kα source.Surface chemical components were analyzed using Thermo VG Scientific Sigma Probe X-ray photoelectron spectroscopy (XPS, Waltham, MA, USA) with an Al-Kα X-ray source.Cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD) were performed using a Metrohm Autolab PGSTAT204 electrochemical workstation (Utrecht, The Netherlands), with potential windows of 0−0.8 V for both, potential scan speeds ranging from 2 to 200 mV/s for CV, and constant currents of 4, 2, 1, and 0.5 mA for GCD.

Water Contact Angle
Figure 2 shows the water contact angle of the as-deposited LiCl-SnCl2•2H2O precursor on carbon cloth and those seen after APPJ treatment.Figure 2a shows that the pristine carbon cloth exhibited hydrophobic characteristics with a high contact angle of 133.18°; this value was consistent with our previous findings.However, the as-deposited samples and those after APPJ treatment were hydrophilic.Figure 2b shows that the water droplets completely penetrated the as-deposited sample surface within about 12 s.By contrast, it penetrated the APPJ-processed samples immediately after the droplet was dispensed.The enhanced hydrophilicity of the Li2SnO3 electrode surface could be attributed to the hydrophilic surface functional group containing nitrogen and oxygen conferred by the APPJ process in a nitrogen working environment [28,29].The improved hydrophilicity promoted contact between the Li2SnO3 Li-HSCs electrode surface and the 1-M Li2SO4 liquid electrolyte, delivering better electrochemical performance [30].

Characterizations of Li 2 SnO 3 and Li-HSCs
A Sindetake Model 100SB goniometer measured the water contact angle of Li 2 SnO 3 onto carbon cloth.The electrode surface morphology was inspected using a JEOL JSM-7800 F Prime scanning electron microscope (SEM) (Tokyo, Japan), equipped with the capacity to perform energy-dispersive X-ray spectroscopy (EDS).The crystallinity of Li 2 SnO 3 was examined using a Bruker D2 Phaser X-ray diffractometer (Billerica, MA, USA) with a Cu-Kα source.Surface chemical components were analyzed using Thermo VG Scientific Sigma Probe X-ray photoelectron spectroscopy (XPS, Waltham, MA, USA) with an Al-Kα X-ray source.Cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD) were performed using a Metrohm Autolab PGSTAT204 electrochemical workstation (Utrecht, The Netherlands), with potential windows of 0−0.8 V for both, potential scan speeds ranging from 2 to 200 mV/s for CV, and constant currents of 4, 2, 1, and 0.5 mA for GCD.

Water Contact Angle
Figure 2 shows the water contact angle of the as-deposited LiCl-SnCl 2 •2H 2 O precursor on carbon cloth and those seen after APPJ treatment.Figure 2a shows that the pristine carbon cloth exhibited hydrophobic characteristics with a high contact angle of 133.18 • ; this value was consistent with our previous findings.However, the as-deposited samples and those after APPJ treatment were hydrophilic.Figure 2b shows that the water droplets completely penetrated the as-deposited sample surface within about 12 s.By contrast, it penetrated the APPJ-processed samples immediately after the droplet was dispensed.The enhanced hydrophilicity of the Li 2 SnO 3 electrode surface could be attributed to the hydrophilic surface functional group containing nitrogen and oxygen conferred by the APPJ process in a nitrogen working environment [28,29].The improved hydrophilicity promoted contact between the Li 2 SnO 3 Li-HSCs electrode surface and the 1-M Li 2 SO 4 liquid electrolyte, delivering better electrochemical performance [30].

SEM
Figure 3 shows SEM images with a magnification rate (5000×).Figure 3b shows that the ethyl cellulose mostly wrapped the as-deposited LiCl-SnCl2•2H2O pastes.The thermal decomposition temperature of ethyl cellulose is about 312 °C [31]; therefore, it is burned out during APPJ treatment (620 °C).The attachment of the residual ethyl cellulose to the electrode surface hinders the ion adsorption and desorption capacity of the liquid electrolyte [32].Figure 3h shows that ethyl cellulose was completely removed after APPJ processing time of 480 s; however, the carbon fibers became rough due to the plasma treatment.Figure 4 shows SEM images with a higher magnification rate (50,000×).As the APPJ processing time increased, we observed that a large amount of Li2SnO3 crystals had grown on the carbon fibers.Figure 4h shows that the 480 s APPJ-processed sample exhibited the best crystallinity.The results demonstrate that high-temperature nitrogen APPJ treatment can be used for the rapid conversion of Li2SnO3.

SEM
Figure 3 shows SEM images with a magnification rate (5000×).Figure 3b shows that the ethyl cellulose mostly wrapped the as-deposited LiCl-SnCl 2 •2H 2 O pastes.The thermal decomposition temperature of ethyl cellulose is about 312 • C [31]; therefore, it is burned out during APPJ treatment (620 • C).The attachment of the residual ethyl cellulose to the electrode surface hinders the ion adsorption and desorption capacity of the liquid electrolyte [32].Figure 3h shows that ethyl cellulose was completely removed after APPJ processing time of 480 s; however, the carbon fibers became rough due to the plasma treatment.Figure 4 shows SEM images with a higher magnification rate (50,000×).As the APPJ processing time increased, we observed that a large amount of Li 2 SnO 3 crystals had grown on the carbon fibers.Figure 4h shows that the 480 s APPJ-processed sample exhibited the best crystallinity.The results demonstrate that high-temperature nitrogen APPJ treatment can be used for the rapid conversion of Li 2 SnO 3 .

SEM
Figure 3 shows SEM images with a magnification rate (5000×).Figure 3b shows that the ethyl cellulose mostly wrapped the as-deposited LiCl-SnCl2•2H2O pastes.The thermal decomposition temperature of ethyl cellulose is about 312 °C [31]; therefore, it is burned out during APPJ treatment (620 °C).The attachment of the residual ethyl cellulose to the electrode surface hinders the ion adsorption and desorption capacity of the liquid electrolyte [32].Figure 3h shows that ethyl cellulose was completely removed after APPJ processing time of 480 s; however, the carbon fibers became rough due to the plasma treatment.Figure 4 shows SEM images with a higher magnification rate (50,000×).As the APPJ processing time increased, we observed that a large amount of Li2SnO3 crystals had grown on the carbon fibers.Figure 4h shows that the 480 s APPJ-processed sample exhibited the best crystallinity.The results demonstrate that high-temperature nitrogen APPJ treatment can be used for the rapid conversion of Li2SnO3.

XRD
Figure 5 shows the XRD patterns of Li2SnO3 electrodes when processed by APPJ for 0 s, 5 s, 30 s, 90 s, 180 s, 300 s, and 480 s. Figure 5a shows the obvious diffraction peaks at 2θ = 26°, which can be attributed to the presence of the carbon cloth [33].The intensity of the diffraction peak was particularly weak in the as-deposited sample because of the covering of the electrode surface with unburned ethyl cellulose.Furthermore, additional diffraction peaks corresponding to the (200) lattice plane of Li2SnO3 were found at 2θ = 34.1°[34].These peaks could be attributed to a monoclinic-layered structure.Figure 5b shows a magnified view of the XRD pattern of the (200) Li2SnO3 lattice plane.No significant peaks were observed in the samples after APPJ processing for 0 s, 5 s, 30 s, 90 s, and 180 s.By contrast, diffraction peaks were observed in the 300 s and 480 s APPJ-processed samples.This phenomenon demonstrates that the monoclinic Li2SnO3 gradually grew on the carbon cloth fiber surface due to the high temperature of the nitrogen APPJ processing and its presence increased with processing time.Furthermore, the better crystallinity of Li2SnO3 helped to improve the electrochemical performance of Li-HSCs.These XRD results of crystallinity are also in good agreement with the SEM results.

XPS
Figure 6 shows the XPS results of Li2SnO3 electrodes processed by APPJ.The chemical configurations of C1s, O1s, and Sn3d, as well as Li1s XPS spectra of Li2SnO3, were

XRD
Figure 5 shows the XRD patterns of Li 2 SnO 3 electrodes when processed by APPJ for 0 s, 5 s, 30 s, 90 s, 180 s, 300 s, and 480 s. Figure 5a shows the obvious diffraction peaks at 2θ = 26 • , which can be attributed to the presence of the carbon cloth [33].The intensity of the diffraction peak was particularly weak in the as-deposited sample because of the covering of the electrode surface with unburned ethyl cellulose.Furthermore, additional diffraction peaks corresponding to the (200) lattice plane of Li 2 SnO 3 were found at 2θ = 34.1 • [34].These peaks could be attributed to a monoclinic-layered structure.Figure 5b shows a magnified view of the XRD pattern of the (200) Li 2 SnO 3 lattice plane.No significant peaks were observed in the samples after APPJ processing for 0 s, 5 s, 30 s, 90 s, and 180 s.By contrast, diffraction peaks were observed in the 300 s and 480 s APPJ-processed samples.This phenomenon demonstrates that the monoclinic Li 2 SnO 3 gradually grew on the carbon cloth fiber surface due to the high temperature of the nitrogen APPJ processing and its presence increased with processing time.Furthermore, the better crystallinity of Li 2 SnO 3 helped to improve the electrochemical performance of Li-HSCs.These XRD results of crystallinity are also in good agreement with the SEM results.

XRD
Figure 5 shows the XRD patterns of Li2SnO3 electrodes when processed by APPJ for 0 s, 5 s, 30 s, 90 s, 180 s, 300 s, and 480 s. Figure 5a shows the obvious diffraction peaks at 2θ = 26°, which can be attributed to the presence of the carbon cloth [33].The intensity of the diffraction peak was particularly weak in the as-deposited sample because of the covering of the electrode surface with unburned ethyl cellulose.Furthermore, additional diffraction peaks corresponding to the (200) lattice plane of Li2SnO3 were found at 2θ = 34.1°[34].These peaks could be attributed to a monoclinic-layered structure.Figure 5b shows a magnified view of the XRD pattern of the (200) Li2SnO3 lattice plane.No significant peaks were observed in the samples after APPJ processing for 0 s, 5 s, 30 s, 90 s, and 180 s.By contrast, diffraction peaks were observed in the 300 s and 480 s APPJ-processed samples.This phenomenon demonstrates that the monoclinic Li2SnO3 gradually grew on the carbon cloth fiber surface due to the high temperature of the nitrogen APPJ processing and its presence increased with processing time.Furthermore, the better crystallinity of Li2SnO3 helped to improve the electrochemical performance of Li-HSCs.These XRD results of crystallinity are also in good agreement with the SEM results.

XPS
Figure 6 shows the XPS results of Li2SnO3 electrodes processed by APPJ.The chemical configurations of C1s, O1s, and Sn3d, as well as Li1s XPS spectra of Li2SnO3, were

XPS
Figure 6 shows the XPS results of Li 2 SnO 3 electrodes processed by APPJ.The chemical configurations of C1s, O1s, and Sn3d, as well as Li1s XPS spectra of Li 2 SnO 3 , were identified.Figure S1 shows the Sn3d 5/2 spectrum, which can be deconvoluted into three peaks at 485.8, 486.9, and 487.6 eV, corresponding to Sn 0+ , Sn 2+ , and Sn 4+ [35,36].Table S1 shows the relative bonding contents obtained from XPS analysis of Sn3d 5/2 .The highest Sn 4+ bonding content arose in the APPJ 480 s case, which indicates that most of the precursors on the electrode surface were transformed into Li 2 SnO 3 crystals via APPJ.This is in good agreement with the SEM and XRD results.Figure S2 shows the Li1s spectra at 54.5-55.5 eV, which proves that the electrode surface really contained Li elements [37].
J. Compos.Sci.2024, 8, x FOR PEER REVIEW 6 of 13 identified.Figure S1 shows the Sn3d 5/2 spectrum, which can be deconvoluted into three peaks at 485.8, 486.9, and 487.6 eV, corresponding to Sn 0+ , Sn 2+ , and Sn 4+ [35,36].Table S1 shows the relative bonding contents obtained from XPS analysis of Sn3d 5/2 .The highest Sn 4+ bonding content arose in the APPJ 480 s case, which indicates that most of the precursors on the electrode surface were transformed into Li2SnO3 crystals via APPJ.This is in good agreement with the SEM and XRD results.Figure S2 shows the Li1s spectra at 54.5-55.5 eV, which proves that the electrode surface really contained Li elements [37].

CV of Li-HSCs s
Figure 7 shows the areal capacity of Li2SnO3 Li-HSCs under various APPJ processing times.The CV results were conducted using potential scan rates of 200, 20, and 2 mV/s within a three-electrode system.The areal capacity Qc (mC/cm 2 ) was calculated using Equation (1): where A is the screen-printed area of the electrode (1.5 cm × 2 cm), v is the potential scan rate, and S is the total area enclosed by the CV curve.Figure S3 shows the CV results measured in the two-electrode symmetric system, and Table 1 shows that the 480 s APPJprocessed Li2SnO3 Li-HSCs had the largest area of those enclosed by the CV curve, with a corresponding areal capacity of 46.113 mC/cm 2 at a scan rate of 2 mV/s.As the APPJ processing time increased, the areal capacity gradually increased because of the removal of ethyl cellulose and the successful conversion of Li2SnO3 crystals.The results also showed

CV of Li-HSCs s
Figure 7 shows the areal capacity of Li 2 SnO 3 Li-HSCs under various APPJ processing times.The CV results were conducted using potential scan rates of 200, 20, and 2 mV/s within a three-electrode system.The areal capacity Q c (mC/cm 2 ) was calculated using Equation (1): where A is the screen-printed area of the electrode (1.5 cm × 2 cm), v is the potential scan rate, and S is the total area enclosed by the CV curve.Figure S3 shows the CV results measured in the two-electrode symmetric system, and Table 1 shows that the 480 s APPJprocessed Li 2 SnO 3 Li-HSCs had the largest area of those enclosed by the CV curve, with a corresponding areal capacity of 46.113 mC/cm 2 at a scan rate of 2 mV/s.As the APPJ processing time increased, the areal capacity gradually increased because of the removal of ethyl cellulose and the successful conversion of Li 2 SnO 3 crystals.The results also showed that the areal capacity was higher under a low potential scan rate owing to the fact that Li-ions of 1-M Li 2 SO 4 liquid electrolyte were available for sufficient time to complete the redox reactions and intercalate/deintercalate effectively on the electrode surface [38].
J. Compos.Sci.2024, 8, x FOR PEER REVIEW 7 of 13 that the areal capacity was higher under a low potential scan rate owing to the fact that Li-ions of 1-M Li2SO4 liquid electrolyte were available for sufficient time to complete the redox reactions and intercalate/deintercalate effectively on the electrode surface [38].

Trasatti Plots of Li-HSCs
Trasatti analysis can assess the respective contributions of EDLC and PC.Its theoretical framework revolves around surface charges and diffusion-controlled charges.We can analyze the differences in the contribution of surface charge (Qout), EDLC, diffusion-controlled charge (Qin), and PC by applying various scan rates in the CV test (Figure 8a-g).As the scan rate decreases towards zero, sufficient time is provided for the enhanced diffusion of charges across both the inner and outer surfaces of the electrode, thereby attaining maximum capacity.By contrast, when the scan rate approaches infinity, only the surface charges contribute to the charge storage mechanism.Figure 8h shows the Qout, the intercept of the vertical axis (when v −1/2 = 0, the scanning rate is infinity), in the plot of Qc versus the horizontal axis v −1/2 .Figure 8i shows the Qtotal (= Qin + Qout), the intercept of the fitted line, and the vertical axis 1/Qc (when v 1/2 = 0).Table 2 shows the calculated capacity contribution of Li2SnO3 Li-HSCs.It exhibited the highest PC in the APPJ 480 s case.As PC is mainly related to redox reactions, the results can be explained by the formation of better Li2SnO3 crystals [39].This outcome was also in good agreement with the previous SEM and XRD analyses.Further, we observed a decrease in EDLC values with 300 s and 480 s APPJ processing.Given that EDLC is mainly related to surface charges, this outcome can be attributed to the damage to the material by the high-temperature APPJ during extended processing periods.

Trasatti Plots of Li-HSCs
Trasatti analysis can assess the respective contributions of EDLC and PC.Its theoretical framework revolves around surface charges and diffusion-controlled charges.We can analyze the differences in the contribution of surface charge (Q out ), EDLC, diffusioncontrolled charge (Q in ), and PC by applying various scan rates in the CV test (Figure 8a-g).As the scan rate decreases towards zero, sufficient time is provided for the enhanced diffusion of charges across both the inner and outer surfaces of the electrode, thereby attaining maximum capacity.By contrast, when the scan rate approaches infinity, only the surface charges contribute to the charge storage mechanism.Figure 8h shows the Q out , the intercept of the vertical axis (when v −1/2 = 0, the scanning rate is infinity), in the plot of Qc versus the horizontal axis v −1/2 .Figure 8i shows the Q total (= Q in + Q out ), the intercept of the fitted line, and the vertical axis 1/Qc (when v 1/2 = 0).Table 2 shows the calculated capacity contribution of Li 2 SnO 3 Li-HSCs.It exhibited the highest PC in the APPJ 480 s case.As PC is mainly related to redox reactions, the results can be explained by the formation of better Li 2 SnO 3 crystals [39].This outcome was also in good agreement with the previous SEM and XRD analyses.Further, we observed a decrease in EDLC values with 300 s and 480 s APPJ processing.Given that EDLC is mainly related to surface charges, this outcome can be attributed to the damage to the material by the high-temperature APPJ during extended processing periods.

𝑄 𝐼 𝑇 𝐴
(2 where A is the area of the electrode (1.5 cm × 2 cm), I is the charging/discharging current, and T is the discharging time [31].Figure 9 and Table 3 show the GCD results in the threeelectrode system.Figure S4 and Table S3 show the GCD results in the two-electrode symmetric system.Together, these findings demonstrate that the Li2SnO3 Li-HSCs processed by APPJ for 480 s had the best performance in terms of areal capacity out of the two types

GCD of Li-HSCs
Figure 9 shows the GCD results of Li 2 SnO 3 Li-HSCs processed by APPJ for 0 s, 5 s, 30 s, 90 s, 180 s, 300 s, and 480 s under constant currents of 4, 2, 1, and 0.5 mA.Equation (2) was used to calculate the areal capacity Qc (µA h/cm 2 ): where A is the area of the electrode (1.5 cm × 2 cm), I is the charging/discharging current, and T is the discharging time [31].Figure 9 and Table 3 show the GCD results in the three-electrode system.Figure S4 and Table S3 show the GCD results in the two-electrode symmetric system.Together, these findings demonstrate that the Li 2 SnO 3 Li-HSCs processed by APPJ for 480 s had the best performance in terms of areal capacity out of the two types of systems.These results also agree with the CV results.Additionally, the change in the slope of the GCD curve under constant currents of 1 and 0.5 mA indicates that Li 2 SnO 3 performed a more obvious redox reaction for a low-discharging current in the three-electrode system [40].This phenomenon was not observed in a two-electrode system because of the measurement inaccuracy caused by polarization currents.Figure 9h shows the Ragone plot, analyzed based on the GCD results.Ragone plots were used to evaluate the energy and power density of the Li 2 SnO 3 Li-HSCs.The energy density E A and power density P A are, respectively, calculated using Equations ( 3) and ( 4): where C A is the areal capacitance obtained from the GCD results, ∆V is the scanning potential window, and T is the discharging time.Table 4 shows that the 480 s APPJprocessed Li 2 SnO 3 Li-HSCs exhibited the best energy density of 5.59 µWh/cm 2 under a discharging current of 0.25 mA.This result indicates that the energy density increased with an increase in APPJ treatment time.Tables 4 and 5 list the energy density and power density of the fabricated Li-HSCs.
of systems.These results also agree with the CV results.Additionally, the change in the slope of the GCD curve under constant currents of 1 and 0.5 mA indicates that Li2SnO3 performed a more obvious redox reaction for a low-discharging current in the three-electrode system [40].This phenomenon was not observed in a two-electrode system because of the measurement inaccuracy caused by polarization currents.Figure 9h shows the Ragone plot, analyzed based on the GCD results.Ragone plots were used to evaluate the energy and power density of the Li2SnO3 Li-HSCs.The energy density EA and power density PA are, respectively, calculated using Equations ( 3) and ( 4): where CA is the areal capacitance obtained from the GCD results, ∆V is the scanning potential window, and T is the discharging time.Table 4 shows that the 480 s APPJ-processed Li2SnO3 Li-HSCs exhibited the best energy density of 5.59 µWh/cm 2 under a discharging current of 0.25 mA.This result indicates that the energy density increased with an increase in APPJ treatment time.Tables 4 and 5

Stability of Li-HSCs
Figure 10 and Table 6 show the results of the 1000-cycle CV stability test in the threeelectrode system (potential scan rate = 20 mV/s) of the 480 s APPJ-processed Li 2 SnO 3 Li-HSCs.The areal capacity of the electrode decreased to 24.72% of the initial performance after 1000 cycles.By contrast, Figure S5 and Table S4 show the results in the two-electrode system; the areal capacity of the electrode decreased to 63.56%.The differences between these two measurement results can be attributed to the polarization current generated by the two-electrode system during the measurement process, resulting in a larger current value being measured and the distortion of the capacity retention rate [41].

Figure 1 .
Figure 1.(a) Fabrication process of the Li2SnO3 Li-HSCs.(b) Evolution of carbon cloth temperature during APPJ processing.

Table 1 .
Areal capacity of Li2SnO3 Li-HSCs calculated based on CV results.

Table 1 .
Areal capacity of Li 2 SnO 3 Li-HSCs calculated based on CV results.

Table 2 .
Capacity contribution of Li2SnO3 Li-HSCs as analyzed using Trasatti method.

Table 2 .
Capacity contribution of Li 2 SnO 3 Li-HSCs as analyzed using Trasatti method.

Table 3 .
Areal capacity of Li 2 SnO 3 Li-HSCs calculated based on GCD results.

Table 4 .
Energy density of Li 2 SnO 3 Li-HSCs calculated based on GCD results.

Table 5 .
Power density of Li 2 SnO 3 Li-HSCs calculated based on GCD results.