Long-Cycle Stability of In Situ Ultraviolet Curable Organic/Inorganic Composite Electrolyte for Solid-State Batteries

Lithium-ion solid-state batteries with spinel Li4Ti5O12 (LTO) electrodes have significant advantages, such as stability, long life, and good multiplication performance. In this work, the LTO electrode was obtained by the atmospheric plasma spraying method, and a composite solid electrolyte was prepared by in situ ultraviolet (UV) curing on the LTO electrode. The composite solid electrolyte was designed using a soft–hard combination strategy, and the electrolyte was prepared into a composite of a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) flexible structure and high-conductivity Li1.3Al0.3Ti1.7(PO4)3 (LATP) hard particles. The composite electrolyte exhibited a good ionic conductivity up to 0.35 mS cm−1 at 30 °C and an electrochemical window above 4.0 V. In situ and ex situ electrolytes were assembled into LTO//electrolyte//Li solid-state batteries to investigate their impact on the electrochemical performance of the batteries. As a result, the assembled Li4Ti5O12//in situ electrolytes//Li batteries exhibited excellent rate of performance, and their capacity retention rate was 90% at 0.2 mA/cm2 after 300 cycles. This work provides a new method for the fabrication of novel advanced solid-state electrolytes and electrodes for applications in solid-state batteries.


Introduction
Since the 20th century, lithium-ion batteries have been widely used in smartphones, laptops, and other portable electronic devices.Currently, lithium-ion batteries are also used as the main power source in electric vehicles, which require lithium batteries to have a long cycle life, high rate of performance, safety, reliability, durability, and low cost [1][2][3].Spinelstructured lithium titanate (Li 4 Ti 5 O 12 , LTO), as a new type of anode material, does not produce lithium dendrites during cycling because of its highly embedded and dislodged lithium potentials (1.55 V vs. Li/Li + ), and its almost zero volume change during charging and discharging (<0.2%) is why it is known as a zero-strain material, which means that this battery has a long cycle life [4][5][6].Due to these properties, LTO is used as an anode material with potential applications in electrochemical energy storage, electric vehicles, and grid stabilization.
However, a series of safety issues arising from a thermal runaway caused by the use of liquid electrolytes in lithium-ion batteries have hindered their future development [7,8].As a result, solid-state batteries are considered the preferred choice for electric vehicles, mobile electronic devices, and other fields.However, solid-state batteries still face many challenges Polymers 2024, 16,55 3 of 11 showed that the stability of the battery was improved and the energy density was also improved to a certain extent.Although much progress has been made, the interface problem between the electrolyte and the positive electrode has not been effectively solved.The interface problems of solid-state batteries still hinder the future development of solid-state batteries.
In this work, we provide a new strategy to reduce the interface impedance between solid electrolytes and electrodes and improve the ion conductivity and high electrochemical performance of the electrolytes.LTO electrodes were prepared by atmospheric plasma spraying, and then a polymer/oxide composite electrolyte precursor solution was directly cast onto the surface of the LTO electrode to prepare an electrolyte layer through an in situ UV curing process.The electrolyte layer was assembled with a metal lithium negative electrode to form an LTO//in situ electrolyte//Li solid-state battery.This solid-state battery exhibits better electrochemical performance.This work provides feasible strategies and process methods for preparing flexible, ultra-thin, and large-area solid-state batteries.

Preparation of LTO Electrodes
LTO powder (Figure 1d,e) was sprayed onto the perforated copper foil at high speed using plasma spraying technology.The perforated copper foil with a thickness of 15 µm was fixed on a copper plate with good heat dissipation.The main gas in the plasma was argon, and hydrogen was used as an auxiliary gas.Spraying parameters are shown in Table 1.The spraying distance was 100 mm, and the plasma current was varied between 500 and 600 A. The macroscopic view of the LTO electrode with a schematic diagram of the preparation process is shown in Figure 1.
all-solid-state electrode/electrolyte stack upon UV irradiation.Rate performance in creased with increasing ionic conductivity, decreased with increasing polymer conten and decreased with increasing oxygen content in the polyacrylate matrix.Shi et al. [2 prepared a thin ZnO layer in situ on both sides of a double-layer Ta-LLZO.Experimen were conducted in order to improve the wettability between the lithium metal and T LLZO (on the anode side), and the results showed that the stability of the battery wa improved and the energy density was also improved to a certain extent.Although muc progress has been made, the interface problem between the electrolyte and the positiv electrode has not been effectively solved.The interface problems of solid-state batterie still hinder the future development of solid-state batteries.
In this work, we provide a new strategy to reduce the interface impedance betwee solid electrolytes and electrodes and improve the ion conductivity and high electrochem ical performance of the electrolytes.LTO electrodes were prepared by atmospheric plasm spraying, and then a polymer/oxide composite electrolyte precursor solution was direct cast onto the surface of the LTO electrode to prepare an electrolyte layer through an in sit UV curing process.The electrolyte layer was assembled with a metal lithium negativ electrode to form an LTO//in situ electrolyte//Li solid-state battery.This solid-state batter exhibits better electrochemical performance.This work provides feasible strategies an process methods for preparing flexible, ultra-thin, and large-area solid-state batteries.

Preparation of LTO Electrodes
LTO powder (Figure 1d,e) was sprayed onto the perforated copper foil at high spee using plasma spraying technology.The perforated copper foil with a thickness of 15 μm was fixed on a copper plate with good heat dissipation.The main gas in the plasma wa argon, and hydrogen was used as an auxiliary gas.Spraying parameters are shown i Table 1.The spraying distance was 100 mm, and the plasma current was varied betwee 500 and 600 A. The macroscopic view of the LTO electrode with a schematic diagram o the preparation process is shown in Figure 1.

Preparation of Composite Solid State Electrolyte
The composite solid electrolyte was prepared by UV solidification method, and the preparation process is shown in Figure 2. 2 g of PVDF-HFP was dissolved in 8 g of DMF, and after dissolving into a transparent viscous solution with stirring at 45 • C, 0.2 g of LATP was added to continue heating and stirring for 6 h.After stirring, 0.5 g of PUA and 0.8 g of ETPTA and HMPP (the concentration of HMPP was fixed at 0.1 wt% of ETPTA) were added.Stirring was continued for 5 min, and the obtained electrolyte precursor solution was poured onto the electrode sheet in a small amount uniformly.The electrolyte precursor solution was uniformly applied to the electrode sheet with a 150 µm spatula, and the remaining electrolyte precursor solution was poured onto the polytetrafluoroethylene (PTFE) plate, after which the electrolyte-stained electrode sheet and the PTFE plate with precursor solution were put into a UV curing machine for 5 min of light solidification and then placed into a drying oven at 60 • C for 30 min.The dried composite electrode sheet and solid electrolyte were cut into Φ18 discs; the solid electrolyte was named USPE as the control.
roscopic diagram of solid electrolyte membrane.

Preparation of Composite Solid State Electrolyte
The composite solid electrolyte was prepared by UV solidification method, and the preparation process is shown in Figure 2. 2 g of PVDF-HFP was dissolved in 8 g of DMF, and after dissolving into a transparent viscous solution with stirring at 45 °C, 0.2 g of LATP was added to continue heating and stirring for 6 h.After stirring, 0.5 g of PUA and 0.8 g of ETPTA and HMPP (the concentration of HMPP was fixed at 0.1 wt% of ETPTA) were added.Stirring was continued for 5 min, and the obtained electrolyte precursor solution was poured onto the electrode sheet in a small amount uniformly.The electrolyte precursor solution was uniformly applied to the electrode sheet with a 150 μm spatula, and the remaining electrolyte precursor solution was poured onto the polytetrafluoroethylene (PTFE) plate, after which the electrolyte-stained electrode sheet and the PTFE plate with precursor solution were put into a UV curing machine for 5 min of light solidification and then placed into a drying oven at 60 °C for 30 min.The dried composite electrode sheet and solid electrolyte were cut into Φ18 discs; the solid electrolyte was named USPE as the control.

LTO Battery Assembly
CR2025-type button cell batteries were assembled in a glove box filled with argon gas.The in situ electrode sheet was immersed in liquid electrolyte for 5 min before battery assembly, and the in situ electrolyte plasma-sprayed LTO electrode sheet was used as the cathode, and lithium metal was used as the anode.The battery was assembled according to the operational steps.

Characterization and Electrochemical Measurements
The physical phase of the samples was analyzed by X-ray diffraction (XRD, D8-AD-VANCE, Bruker, Karlsruhe, Germany, Cu, 40 k V, 40 m A) with a radiation angle between

LTO Battery Assembly
CR2025-type button cell batteries were assembled in a glove box filled with argon gas.The in situ electrode sheet was immersed in liquid electrolyte for 5 min before battery assembly, and the in situ electrolyte plasma-sprayed LTO electrode sheet was used as the cathode, and lithium metal was used as the anode.The battery was assembled according to the operational steps.

Characterization and Electrochemical Measurements
The physical phase of the samples was analyzed by X-ray diffraction (XRD, D8-ADVANCE, Bruker, Karlsruhe, Germany, Cu, 40 k V, 40 m A) with a radiation angle between 10 • and 90 • in steps of 0.1 • .A scanning electron microscope (SEM; GeminiSEM 500, ZEISS Inc., Jena, Germany) was used to observe the microscopic morphology of the plasma-sprayed LTO electrodes.The prepared in situ battery samples were charged and discharged using the NEWARE battery test system (CT-4008).Electrochemical impedance spectroscopy (EIS) was performed on the samples using an electrochemical workstation (CHI660E) in the frequency range of 0.1~10 5 Hz at room temperature.

Electrochemical Measurements
The timing current of the lithium symmetric battery was tested at a voltage of 0.5 mV, lasting 4000 s, and the formula was as follows: The lithium-ion transference number (t Li+ ) can be obtained.I 0 and I s are current values after DC polarization starts and stabilizes, R 0 and R s are the impedance values before and after the DC polarization, and ∆V is the value of the voltage applied to both ends of the battery.For the ionic conductivity test, the battery assembly used stainless steel (SS) as a symmetrical battery and an electrochemical impedance test together to calculate the ionic conductivity.The frequency range of the impedance test is 0.1~10 6 Hz.
where σ represents the ionic conductivity, L is the thickness of the electrolyte, S represents the contact area between the electrolyte and the test electrode (SS), and R is the impedance value of the battery electrolyte measured by EIS.Linear sweep voltammetry (LSV) was used to perform electrochemical window tests at 2.5~6 V at a scanning rate of 0.1 mV s −1 .

Results
We measured the active material loading of the LTO electrode monolith as 3.8 mg and the total mass loading as 5.4 mg.As shown in Figure 3, after plasma spraying, the SEM image of the LTO electrode shows that a lithium titanate functional coating was formed by stacking on the porous copper foil, with a small amount of unmelted spherical, LTO small particles on the surface.Figure 3a shows a macro image of the LTO electrodes and in situ solid electrolyte, which indicates that both LTO electrodes and solid electrolytes are flexible.Figure 3b shows the macroscopic view of the LTO electrode after spraying, indicating that the battery electrode made in this way does not need the complex process of slurry coating, and the electrode size is no longer limited by the limitations of the scraping and coating tools, which can meet the needs of personalization.Figure 3c,d show the microscopic magnification of the macroscopic electrode; it can be observed that the LTO powder is uniformly attached to the porous copper foil.Figure 3e is a further enlarged micrograph of the micro surface of the LTO electrode, from which the stacked morphology of the electrode surface can be observed, indicating that during the spraying process, the LTO powder is melted and stacked onto the porous copper foil and then cooled to form the stacked morphology.A large number of Ti and O are observed on the LTO electrode surface (Figure 3f).
The phase structure of the polymer electrolyte was investigated by XRD (Figure 4a).Pure ETPTA showed three visible crystal diffraction peaks near 12.8 • , 22.3 • , and 45.8 • .The composite solid electrolyte USPE showed broad peaks between 15 • and 25 • and no other crystallization peaks, indicating that the USPE was in an amorphous state, which is conducive to the enhancement of Li + ion transfer in the composite electrolyte [28].ETPTA monomers with three C=C double bonds act as cross-linking agents and can form threedimensional cross-linked networks by free radical polymerization.The ETPTA crosslinked network and PVDF-HFP chains can form a semi-interpenetrating network skeleton, in which the linear PUA chains and PVDF-HFP chains can soften the ETPTA rigid network, thus improving the contact between the electrodes and the electrolyte [29].The lithium ion transference number (tLi+) before and after DC polarization was determined by combining the timed-current method and electrochemical impedance spectroscopy (EIS) measurements, as shown in Figure 4b.According to the BVE equation [19], tLi+ = 0.71 for the USPE electrolyte at room temperature.Figure 4c shows that the electrochemical window is higher than 4.0 V, indicating that the USPE electrolyte has high voltage resistance characteristics.As shown in Figure in which the linear PUA chains and PVDF-HFP chains can soften the ETPTA rigid network, thus improving the contact between the electrodes and the electrolyte [29].The lithium ion transference number (tLi+) before and after DC polarization was determined by combining the timed-current method and electrochemical impedance spectroscopy (EIS) measurements, as shown in Figure 4b.According to the BVE equation [19], tLi+ = 0.71 for the USPE electrolyte at room temperature.Figure 4c shows that the electrochemical window is higher than 4.0 V, indicating that the USPE electrolyte has high voltage resistance characteristics.As shown in Figure  The lithium ion transference number (t Li+ ) before and after DC polarization was determined by combining the timed-current method and electrochemical impedance spectroscopy (EIS) measurements, as shown in Figure 4b.
According to the BVE equation [19], t Li+ = 0.71 for the USPE electrolyte at room temperature.Figure 4c shows that the electrochemical window is higher than 4.0 V, indicating that the USPE electrolyte has high voltage resistance characteristics.As shown in Figure 4d, the ionic conductivity of USPE exhibits an increasing trend with increasing temperature, and the ionic conductivity reaches a maximum value of 0.65 mS cm −1 at 80 • C.Not only that, USPE also exhibits good ionic conductivity of up to 0.35 mS cm −1 at 30 shows that the impedance values of the USPE electrolyte at different temperatures display a minimum impedance at 80 • C. Figure 4f shows that USPE has two weight loss stages.The first stage occurs at 190 • C due to the evaporation of a small amount of water remaining in USPE.The second stage occurs at 400 • C, and the reason for weight loss is thermal reactions, indicating that the USPE electrolyte has high thermal stability [30].
Figure 5a depicts the FITR spectra of the USPE electrolyte.The characteristic peaks appearing at 761, 872, 1065, and 1400 cm −1 represent the CF 2 bending and skeletal bending, C-H rocking, amorphous phase belt, C-C stretching, and CH 2 deformation, which come from pure PVDF-HFP [21].Figure 5c depicts the DSC spectra of USPE.The pure PVDF-HFP membrane has an endothermic peak near 146.1 • C, which is the melting temperature (T m ) of PVDF-HFP [22].Obviously, an endothermic peak appears in the DSC curve near 55 • C, indicating that the Tm of ETPTA and PVDF-HFP decreased to 55.5 • C. It is worth mentioning that the lower crystallinity is beneficial to increasing the disordered region of the system, which makes the organic chain more disordered and free and enhances the ionic conductivity and lithium ion migration number of the electrolyte.The membrane has the endothermic peak at around 146.1 • C, which is the melt temperature (Tm) of the PVDF-HFP [31].Figure 5b shows the performance radar diagrams of the three electrolytes of USPE, PVDF-LLZTO [32], and PEO-TN [33].USPE showed good thermal stability, high ionic conductivity, and high t Li+ .The ionic conductivity and t Li+ of USPE are greater than those of the other two electrolytes.The ionic conductivity and t Li+ are important factors to evaluate the solid electrolyte.A high ionic conductivity and t Li+ can reduce the concentration polarization of the battery during charging and discharging, showing a better rate performance and smaller resistance.However, the electrochemical window of USPE is smaller than that of the other two electrolytes, but because the operating voltage (1-3 V) of LTO is much smaller than 4 V, the lower electrochemical window has little effect on the LTO battery.Overall, the USPE electrolyte exhibits good overall performance in terms of ion conductivity, t Li+ , electrochemical window, good flexibility, thermal stability, and flammability.Overall, the USPE electrolyte exhibited good overall performance in terms of ion conductivity, t Li+ , electrochemical window, good flexibility, thermal stability, and flammability.
4d, the ionic conductivity of USPE exhibits an increasing trend with increasing temperature, and the ionic conductivity reaches a maximum value of 0.65 mS cm −1 at 80 °C.Not only that, USPE also exhibits good ionic conductivity of up to 0.35 mS cm −1 at 30 °C. Figure 4e shows that the impedance values of the USPE electrolyte at different temperatures display a minimum impedance at 80 °C. Figure 4f shows that USPE has two weight loss stages.The first stage occurs at 190 °C due to the evaporation of a small amount of water remaining in USPE.The second stage occurs at 400 °C, and the reason for weight loss is thermal reactions, indicating that the USPE electrolyte has high thermal stability [30].
Figure 5a depicts the FITR spectra of the USPE electrolyte.The characteristic peaks appearing at 761, 872, 1065, and 1400 cm −1 represent the CF2 bending and skeletal bending, C-H rocking, amorphous phase belt, C-C stretching, and CH2 deformation, which come from pure PVDF-HFP [21].Figure 5c depicts the DSC spectra of USPE.The pure PVDF-HFP membrane has an endothermic peak near 146.1 °C, which is the melting temperature (Tm) of PVDF-HFP [22].Obviously, an endothermic peak appears in the DSC curve near 55 °C, indicating that the Tm of ETPTA and PVDF-HFP decreased to 55.5 °C.It is worth mentioning that the lower crystallinity is beneficial to increasing the disordered region of the system, which makes the organic chain more disordered and free and enhances the ionic conductivity and lithium ion migration number of the electrolyte.The membrane has the endothermic peak at around 146.1 °C, which is the melt temperature (Tm) of the PVDF-HFP [31].Figure 5b shows the performance radar diagrams of the three electrolytes of USPE, PVDF-LLZTO [32], and PEO-TN [33].USPE showed good thermal stability, high ionic conductivity, and high tLi+.The ionic conductivity and tLi+ of USPE are greater than those of the other two electrolytes.The ionic conductivity and tLi+ are important factors to evaluate the solid electrolyte.A high ionic conductivity and tLi+ can reduce the concentration polarization of the battery during charging and discharging, showing a better rate performance and smaller resistance.However, the electrochemical window of USPE is smaller than that of the other two electrolytes, but because the operating voltage (1-3 V) of LTO is much smaller than 4 V, the lower electrochemical window has little effect on the LTO battery.Overall, the USPE electrolyte exhibits good overall performance in terms of ion conductivity, tLi+, electrochemical window, good flexibility, thermal stability, and flammability.Overall, the USPE electrolyte exhibited good overall performance in terms of ion conductivity, tLi+, electrochemical window, good flexibility, thermal stability, and flammability.As shown in Figure 6a,b, the surface of the in situ USPE electrolyte sheet before cycling is covered with several small pores of 10 μm or less, and after magnification to 5000×, as shown in Figure 6b, the white dots on the surface of the in situ USPE electrolyte are the Li1.3Al0.3Ti1.7(PO4)3(LATP) ceramic particles, and the LATP ceramic particles can be seen to be uniformly distributed on the electrode surface.As shown in Figure 6e, the morphology of the LATP ceramic particles changes compared with the surface of the electrolyte before As shown in Figure 6a,b, the surface of the in situ USPE electrolyte sheet before cycling is covered with several small pores of 10 µm or less, and after magnification to 5000×, as shown in Figure 6b, the white dots on the surface of the in situ USPE electrolyte are the Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) ceramic particles, and the LATP ceramic particles can be seen to be uniformly distributed on the electrode surface.As shown in Figure 6e, the morphology of the LATP ceramic particles changes compared with the surface of the electrolyte before the cycle.The well-crystallized original LATP particles before the cycle are broken into smaller particles, which means that the LATP in the composite electrolyte reacts with the metal lithium, and the lithiation product is mainly the lithium-rich phase Li 3 Al 0.3 Ti 1.7 (PO 4 ) 3 .Therefore, it can be inferred that the white particles in Figure 6e should be the lithium-rich phase Li 3 Al 0.3 Ti 1.7 (PO 4 ) 3 .This lithiation product has a high electronic Polymers 2024, 16, 55 8 of 11 conductivity, resulting in a series of chemical reactions and destroying the interface between the electrolyte and the electrode [34].From the plasma-sprayed electrode cross-section SEM image (Figure 6c), it can be seen that the thickness of the sprayed LTO is about 2-5 µm.The thickness of the USPE electrolyte can be seen in the in situ electrode cross-section SEM image, which is about 7-14 µm (Figure 6f). the cycle.The well-crystallized original LATP particles before the cycle are broke smaller particles, which means that the LATP in the composite electrolyte reacts wi metal lithium, and the lithiation product is mainly the lithium-rich phase Li3Al0.3Ti1.7 Therefore, it can be inferred that the white particles in Figure 6e should be the lit rich phase Li3Al0.3Ti1.7 (PO4)3.This lithiation product has a high electronic conduc resulting in a series of chemical reactions and destroying the interface between the trolyte and the electrode [34].From the plasma-sprayed electrode cross-section SEM age (Figure 6c), it can be seen that the thickness of the sprayed LTO is about 2-5 μm thickness of the USPE electrolyte can be seen in the in situ electrode cross-section image, which is about 7-14 μm (Figure 6f). Figure 7 shows the charge/discharge, cyclic, and rate performance of the in sit ex batteries.Figure 7a shows that the first stabilized discharge specific capacity in situ battery reached 56 mAh g −1 at 0.2 mA/cm 2 , the capacity retention of the in sit tery is 90%, and the capacity retention of the ex situ battery is 78.8% after 300 cycles thermore, after 600 cycles at 0.4 mA/cm 2 , the first discharge specific capacity of the i battery reached 39.4 mAh g −1 , close to two times the discharge specific capacity (19.75 g −1 ) of the ex situ battery (Figure 7b).The capacity retention rate of the in situ batter 76.4%, and the capacity retention rate of the ex situ battery was about 89.8%.It ind that in the case of increasing current density, the capacity fading of in situ batte smaller, and they have a long cycle life.The rate performance curve (Figure 7c) show the in situ battery can maintain a discharge specific capacity of approximately 22 mA at a current density of 0.8 mA/cm 2 , while the ex situ battery specific capacity decrea 0 mAh g −1 , indicating that the in situ battery can withstand higher charge/discharge This is because in situ batteries avoid the large interface impedance generated by contacts between electrodes and solid electrolytes (Figure 7d),and are more adapta volume changes during battery charging and discharging processes.Figure 7e,f sho charge/discharge curves of in situ and ex situ batteries at 0.4 mA/cm 2 and 0.8 mA/cm voltage plateaus of the two batteries are close to each other, and the charge/discharg cific capacities of both in situ batteries are greater than those of the ex situ batteries.all, the electrochemical performance of in situ batteries is superior to that of ex situ b ies. Figure 7 shows the charge/discharge, cyclic, and rate performance of the in situ and ex situ batteries.Figure 7a shows that the first stabilized discharge specific capacity of the in situ battery reached 56 mAh g −1 at 0.2 mA/cm 2 , the capacity retention of the in situ battery is 90%, and the capacity retention of the ex situ battery is 78.8% after 300 cycles.Furthermore, after 600 cycles at 0.4 mA/cm 2 , the first discharge specific capacity of the in situ battery reached 39.4 mAh g −1 , close to two times the discharge specific capacity (19.75 mAh g −1 ) of the ex situ battery (Figure 7b).The capacity retention rate of the in situ battery was 76.4%, and the capacity retention rate of the ex situ battery was about 89.8%.It indicates that in the case of increasing current density, the capacity fading of in situ batteries is smaller, and they have a long cycle life.The rate performance curve (Figure 7c) shows that the in situ battery can maintain a discharge specific capacity of approximately 22 mAh g −1 at a current density of 0.8 mA/cm 2 , while the ex situ battery specific capacity decreases to 0 mAh g −1 , indicating that the in situ battery can withstand higher charge/discharge rates.This is because in situ batteries avoid the large interface impedance generated by point contacts between electrodes and solid electrolytes (Figure 7d),and are more adaptable to volume changes during battery charging and discharging processes.Figure 7e,f show the charge/discharge curves of in situ and ex situ batteries at 0.4 mA/cm 2 and 0.8 mA/cm 2 .The voltage plateaus of the two batteries are close to each other, and the charge/discharge specific capacities of both in situ batteries are greater than those of the ex situ batteries.Overall, the electrochemical performance of in situ batteries is superior to that of ex situ batteries.

Figure 2 .
Figure 2. Schematic diagram of the preparation process of in situ polymer-ceramic composite solidstate electrolyte.

Figure 2 .
Figure 2. Schematic diagram of the preparation process of in situ polymer-ceramic composite solid-state electrolyte.
15, x FOR PEER REVIEW 6 of 11in which the linear PUA chains and PVDF-HFP chains can soften the ETPTA rigid network, thus improving the contact between the electrodes and the electrolyte[29].

Figure 3 .
Figure 3. (a,b) Image of an LTO electrode prepared by atmospheric plasma spraying.(c-e) SEM images of LTO electrodes.(f) LTO electrode EDS.

Figure 4 .
Figure 4. (a) XRD for USPE, PVDF-HFP, LATP, and ETPTA.(b) Room temperature chronoamperometry of the Li/USPE/Li cell at a potential step of 5 mV and AC impedance spectra of the symmetric cell before and after polarization (inset).(c) LSV curves of USPE at a scanning rate of 0.1 mV s −1 at 25 °C.(d) Arrhenius plots for the ionic conductivity of USPE at different temperatures.(e) Nyquist curves of USPE in the frequency range of 0.1-10 6 MHz in the temperature range of 30° to 80 °C.(f) TG diagram of USPE.

Figure 3 .
Figure 3. (a,b) Image of an LTO electrode prepared by atmospheric plasma spraying.(c-e) SEM images of LTO electrodes.(f) LTO electrode EDS.

Figure 3 .
Figure 3. (a,b) Image of an LTO electrode prepared by atmospheric plasma spraying.(c-e) SEM images of LTO electrodes.(f) LTO electrode EDS.

Figure 4 .
Figure 4. (a) XRD for USPE, PVDF-HFP, LATP, and ETPTA.(b) Room temperature chronoamperometry of the Li/USPE/Li cell at a potential step of 5 mV and AC impedance spectra of the symmetric cell before and after polarization (inset).(c) LSV curves of USPE at a scanning rate of 0.1 mV s −1 at 25 °C.(d) Arrhenius plots for the ionic conductivity of USPE at different temperatures.(e) Nyquist curves of USPE in the frequency range of 0.1-10 6 MHz in the temperature range of 30° to 80 °C.(f) TG diagram of USPE.

Figure 4 .
Figure 4. (a) XRD for USPE, PVDF-HFP, LATP, and ETPTA.(b) Room temperature chronoamperometry of the Li/USPE/Li cell at a potential step of 5 mV and AC impedance spectra of the symmetric cell before and after polarization (inset).(c) LSV curves of USPE at a scanning rate of 0.1 mV s −1 at 25 • C. (d) Arrhenius plots for the ionic conductivity of USPE at different temperatures.(e) Nyquist curves of USPE in the frequency range of 0.1-10 6 MHz in the temperature range of 30 • to 80 • C. (f) TG diagram of USPE.

Figure 6 .
Figure 6.SEM images of (a,b) surface of USPE on the electrodes.(c) LTO electrode cross-s (d,e) Surface of USPE on the LTO electrodes after 600 cycles.(f) Cross-section of in situ USPE LTO electrode.

Figure 6 .
Figure 6.SEM images of (a,b) surface of USPE on the LTO electrodes.(c) LTO electrode cross-section.(d,e) Surface of USPE on the LTO electrodes after 600 cycles.(f) Cross-section of in situ USPE on the LTO electrode.

Table 1 .
Spray data table.

Table 1 .
Spray data table.