All-fiber tribo-ferroelectric synergistic electronics with high thermal-moisture stability and comfortability

Developing fabric-based electronics with good wearability is undoubtedly an urgent demand for wearable technologies. Although the state-of-the-art fabric-based wearable devices have shown unique advantages in the field of e-textiles, further efforts should be made before achieving “electronic clothing” due to the hard challenge of optimally unifying both promising electrical performance and comfortability in single device. Here, we report an all-fiber tribo-ferroelectric synergistic e-textile with outstanding thermal-moisture comfortability. Owing to a tribo-ferroelectric synergistic effect introduced by ferroelectric polymer nanofibers, the maximum peak power density of the e-textile reaches 5.2 W m−2 under low frequency motion, which is 7 times that of the state-of-the-art breathable triboelectric textiles. Electronic nanofiber materials form hierarchical networks in the e-textile hence lead to moisture wicking, which contributes to outstanding thermal-moisture comfortability of the e-textile. The all-fiber electronics is reliable in complicated real-life situation. Therefore, it is an idea prototypical example for electronic clothing.

Supplementary Note 11. Interpretation of signal processing, real-time mapping, and foot pressure sensing in self-charging, self-sensing gesture monitoring system.

. The effect of primary polarization direction (θ) and thickness (D SFP ) of ferroelectricity on the performance of SFP e-textile.
When the detection between primary polarization and effective electric field (ED + Ep) change from same to opposite, the output voltage and current are significantly improved ( Figure S5b). Because the smaller the θ, the more difficult it is for dipoles to reach the equilibrium position, resulting in a smaller residual polarization and lower performance. The relationship between output performance and thickness is shown in Figure S5c, and d. The results can be explained by the fact that the increasing of thickness leads to an opposite trend between the amounts of dipoles and internal electric field intensity.
In order to prepare an unpolarized P(VDF-TrFE) nanofiber nonwovens that has the same microstructure as the originally polarized nanofiber ferroelectricity, we proposed the idea of "depolarization" (Figure S8a) [2] . Here, we treated the electrospun P(VDF-TrFE) nanofiber nonwovens at different temperatures to study the depolarization behavior and microstructure changes ( Figure S8b, c, and d). As the heat treatment temperature increases, the d33 of P(VDF-TrFE) ferroelectricity decreases continuously. When temperature reaches 190 °C, the nanofibers begin to melt and the microscopic morphology changes, which would change the surface friction behavior and affect the charge transfer process. When the temperature is higher than 180 °C, the d33 value does not decrease significantly, which indicates that the heat treatment at 180 °C for 3 h is a suitable depolarization process of P(VDF-TrFE) without significantly changing its microstructure. Figure S8e, f, and g shows the circuit diagram of the d33 test. Therefore, the P(VDF-TrFE) obtained by heat treatment at 180 ℃ for 3 hours can be considered to have completely depolarized. This sample was use in the preparation of unpolarized ferroelectric (UP) e-textile for control experiments.

Supplementary Note 3. Comparison of electrical properties of UP, SFP and DFP e-textiles to
verify the tribo-ferroelectric synergistic mechanism. Figure S9a shows the process of charges accumulation in three e-textiles step by step. The UP etextile reaches a maximum value of ~106 μCꞏm -2 only after 1100 cycles operation, while the SFP and DFP e-textiles increase with a much bigger slope and reach the maximum value of ~161 μC m -2 after 2800 cycles and ~320 μC m -2 after 6600 cycles. Similarly, with the continue of contact-separate processes, the DFP e-textile has the fastest growth rate and the highest saturation current (~33 μA).

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The current growth rate and saturation current (~16 μA) of SFP e-textile are higher than those of UP e-textile (~10 μA). In addition, during the contact-separation process, we also tested the surface potential of tribo-negative material (P(VDF-TrFE)). It was detected every 10 seconds, and the distance between probe and the textile was fixed at 1.5 cm ( Figure S9c). In 600 seconds, the surface potential of P(VDF-TrFE) in UP e-textile increased from -0.3 kV to -1.05 kV, while the SFP and DFP textiles increased from -0.34 kV and -0.29 kV to -1.91 kV and -3.1 kV, respectively. It visually shows the accumulation of triboelectric charges step by step. And the surface charges accumulation rate and charge density at the friction interface were significantly improved due to the tribo-ferroelectric synergistic enhancement mechanism. As shown in Figure S9d, the output voltage results have similar trend.

Supplementary Note 4. Detailed description of the tribo-ferroelectric synergistic mechanism in
DFP e-textile.
The e-textile consists of two nanofiber nonwovens P(VDF-TrFE) and PA6 with opposite tribopolarity for contact electrification, Ni-Cu fabric electrode for charge induction. The P(VDF-TrFE) nanofibers also act as a polymer ferroelectricity (defined as inner/outer ferroelectric layers) for constructing tribo-ferroelectric synergistic enhancement effect ( Figure S10). The in-situ polarization effect of electrospinning P(VDF-TrFE) is shown in Figure S10a. When PA6 and P(VDF-TrFE) are in contact, they will acquire net opposite charges on their surfaces (b). Once PA6 is separated from P(VDF-TrFE), electrons flow from fabric electrode II to fabric electrode I (c). Meanwhile, the induced potential between two charged surfaces will result in a second polarization of P(VDF-TrFE) ferroelectricity. The polarization of P(VDF-TrFE) ferroelectricity will keep enhanced until the distance between two tribo-polarity materials reaches maximum (d). As the separation distance decreases, the polarization of P(VDF-TrFE) ferroelectricity will gradually decrease until the PA6 contact with P(VDF-TrFE) again (e). Due to dielectric hysteresis [3][4][5] , however, the polarization inside the inner and outer ferroelectric layers will not fully diminish, and the residual built-in dielectric polarization will act as positive and negative charge trap to enhance the capability of capturing charges during contact electrification (f).

Supplementary Note 5. Effect of PA6 layer thickness on water evaporation rate of moisture wicking fabric.
To evaluate the effect of PA6 layer thickness on water evaporation rate of the fabricated textiles, top layer (PAN) thickness and the volume of sweat (200 μL) were kept constant. The increase in the thickness of PA6 layer enriches the mass of the layer, thereby enhancing the water absorption capacity of moisture wicking fabric and also giving rise to the wettability gradient between two layers (From 24 light blue to dark blue) [6,7] . Since the PA6 layer has a faster penetration and spreading driving force ( Figure S12b) than PAN layer, more sweat enrichment in PA6 layer will be more conducive to evaporation. As shown in Figure S12c and d, with the increase of PA6 layer thickness (from 0 μm, 40±6 μm, 70±8 μm to 85±5 μm), the water evaporation rate of moisture wicking fabric increases.
Since the thickness of 85±5 μm of PA6 layer is enough to pull out almost all water from the top (PAN) layer, the water evaporation rate gradually reaches saturation as the thickness of PA6 further increases (from 85±5 μm, 95±9 μm to 100±6 μm).

Supplementary Note 6. Thermal resistance and evaporative resistance test methods and
calculation formulas for functional textiles [8] .
Thermal resistance test: To simulate the skin of human body and its surrounding area, the SGHP consists of three independently controlled heating zones: test plate, guard ring and lower guard. Each zone is heated to the same temperature (typically 35 °C, close to human skin temperature) to eliminate heat transfer between the different zones ( Figure S14b). Therefore, all heat loss will only pass through the fabric to surrounding environment (typically 25 °C). The thermal energy (Q) required to maintain the set temperature for each zone is measured. Thermal resistance can be expressed as where Tskin is the test plate temperature (°C); Tamb is the ambient air temperature (°C); Q/A is the test plate heat flow (W m -2 ).

Evaporation resistance test:
A vapor barrier layer, such as fiberglass paper, was placed between the test plate and the sample to keep the liquid water from wetting the sample. This method allows water vapor to pass through the vapor barrier while the liquid can't pass through ( Figure S14b) As shown in Figure S16a, after introducing 210 g m -2 of sweat onto the surface of hogskin, the relative humidity of friction material gradually increased from 30 to ~50 %, and lasted for about 10 min at 50 % RH. Correspondingly, the output voltage (under 100 MΩ load) of e-textile was gradually reduced from 1110 to ~800 V, and maintained for about 10 min (the voltage data in Figure 4d is obtained at this stage). Subsequently, the relative humidity of friction material gradually decreased to 30 % and reached equilibrium, and the corresponding voltage also raised to equilibrium. So far, the moisture wicking process have undergone a cycle, lasting about 30 minutes. For e-textile without moisture wicking fabric, the relative humidity of friction surface raised from 30 to 83%, and maintained for about 60 minutes at a high relative humidity. The voltage also had a similar trend at this stage, from 1100 to ~300 V. The whole cycle time is about 160 minutes as shown in Figure S16c.
At the end of each moisture wicking process, the output voltage of the electronic textile can be gradually recovered, but less than the initial output voltage. This may be caused by the influence of residual salt such as sodium chloride (NaCl) in e-textile on output voltage. It is noteworthy that after washing and drying, the output voltage of e-textile can return to initial state.

Supplementary Note 8. Description of the washing test.
3 mL of laundry detergent, 600 mL of deionized water and energy textile were first added to the beaker, and magnetic stirring was performed at 600 rpm to simulate the washing environment.
Wherein e-textile is placed directly into the wash solution without any packaging. The wash cycle time was 30 min. Finally, the e-textile was naturally dried for subsequent electrical output measurements ( Figure S17).

Supplementary Note 9. Interpretation of the comparison method of output power density in triboelectric textiles.
We systematically sorted out the electrical performance output and measurement conditions of the energy textiles to the best our knowledge. These triboelectric textiles are mainly divided into three categories: All-yarn (breathable), All-fabric (breathable) and Airtight (impermeable) as shown in Figure S18f, and Table S1 . It should be noted that the voltages and currents listed in table are the corresponding outputs of peak power density.

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Supplementary Note 10. Free falling impact test proves that e-textile has certain pressure sensing characteristics.
In order to prove that e-textile has certain pressure sensing characteristics, we used a golf ball with a diameter of 43 mm and a mass of 50 g for free fall impact experiments to simulate the pressure on etextile when walking (Figure 20a). We use the Keithley 2657A to test the voltage signal produced by each impact of e-textile and use a digital camera to record the time and height of each free fall of the golf ball. The magnitude of the force each time the golf ball hits e-textile is calculated using the formula ℎ (5) Related experimental data are shown in Table S2. Figure S20b and c show that the calculated value of the impact force of e-textile has a good linear relationship with the output voltage signal.
Supplementary Note 11. Interpretation of signal processing, real-time mapping, and foot pressure sensing in self-charging and self-sensing gesture monitoring system.
The analog signal processing and wireless transmission unit consists of a processor chip Atmega328P and a wireless transmission module HC-06, mainly adopting analog-to-digital conversion (ADC), digital filtering noise reduction and transmission technology. When processed electrical signals are transmitted to Atmega328P, they are converted to digital signals and filtered by an algorithm. Then, the HC-06 establishes wireless data transmission in 2.4G Hz band with external devices such as a smart phone and personal computer ( Figure S21a). After mobile terminal receives the data, it performs real-time data drawing ( Figure S21b). In addition, the data collected by mobile terminal can also be transmitted to the Internet and cloud mega data. It is expected to realize online real-time monitoring feedback, online diagnosis and the other functions.