Ultrathick MoS2 Films with Exceptionally High Volumetric Capacitance

Manufacturing electrode films at an industrial‐level submillimeter thickness (≈100 µm) with superior volumetric performance is of practical significance for the commercialization of miniaturized supercapacitor systems. This work proposes a commercially scalable solvated‐ion‐intercalated hydrothermal strategy to demonstrate a record‐high volumetric capacitance (511.29 F cm−3) for supercapacitors based on an industrial‐level submillimeter MoS2 film electrode (94.2 µm). The intercalated solvated Li+ ions increase the amount of negative surface charge and reduce the formation energy of 1T MoS2, leading to a high metallic phase content of 82.7% with enhanced electrical conductivity. Together with the expanded interlayer distance (≈1.23 nm), this allows rapid electron transfer and ion transport in the excessively stacked ultrathick MoS2 film to be simultaneously realized. Thus, the as‐fabricated MoS2||graphene/carbon nanotube asymmetric supercapacitor presents both high energy and power densities, outperforms those of commercial devices, including supercapacitors with submillimeter‐thick electrodes and even micrometer‐thick electrodes.


DOI: 10.1002/aenm.202103394
to their widely recognized large surface area, high packing density, and excel lent electrical conductivity, 2D nano materials are of particular interest as new electrodes for supercapacitors with high volumetric performance, which is a more pertinent figureofmerit than the traditionally used gravimetric per formance, particularly for miniaturized and portable supercapacitor devices. [10][11][12][13][14] So far, high volumetric capacitances have been achieved in the micrometer thick electrodes of 2D nanomaterials, for example, ≈1500 F cm −3 for a 3µmthick transition metal carbides (MXene) film, [14] 1445 F cm −3 for a ≈3.3µmthick MXene/ graphene film, [15] ≈700 F cm −3 for a 5µmthick MoS 2 film, [16] and ≈572 F cm −3 for a 7.8µmthick graphene/polyaniline (PANI) composite, [17] which significantly overwhelm the traditional activated carbon counterpart (60≈100 F cm −3 at a similar thickness). [18] However, aiming at industrial real applications, a sufficient mass loading of electrodes is essen tial. [2,5,19,20] As previously reported, graphene electrodes can reach a high energy density of 110.6 Wh kg −1 at a micrometer level thickness of 5.6 µm. [21] When it is fabricated into an industrialstandard packaged supercapacitor cell, however, the weight of passive components, such as separator, electrolyte, and current collectors, need to be considered [20] and the weight of active material will only account for ≈2.5% of the total mass of the packaged cell. As a result, the energy density will trans late to ≈2.8 Wh kg −1 for the packaged device, which is ≈2 times smaller than that of a commercial supercapacitor based on ≈100 µm carbon electrodes (6 Wh kg −1 ) and ≈40 times smaller than that of the 5.6µm graphene electrode (110.6 Wh kg −1 ). Thus, a submillimeterlevel electrode thickness with a high energy density is significantly important for practical applica tions, though highly challenging. For 2D nanomaterials, an increase in film thickness from micrometer to submillimeter level usually causes severely deteriorated performance. [22] As such, the development of 2D nanomaterial electrodes with high volumetric performance at an industriallevel thickness is of particular importance and has recently attracted great atten tion. For example, MXene film (75 µm) developed by Gogotsi and colleagues [18] and graphene/PANI composite (120 µm) developed by Yang and colleagues [23] presented high volu metric capacitances of 330 and 450 F cm −3 , respectively. These achievements show a huge promise of the scalability of 2D Manufacturing electrode films at an industrial-level submillimeter thickness (≈100 µm) with superior volumetric performance is of practical significance for the commercialization of miniaturized supercapacitor systems. This work proposes a commercially scalable solvated-ion-intercalated hydrothermal strategy to demonstrate a record-high volumetric capacitance (511.29 F cm −3 ) for supercapacitors based on an industrial-level submillimeter MoS 2 film electrode (94.2 µm). The intercalated solvated Li + ions increase the amount of negative surface charge and reduce the formation energy of 1T MoS 2 , leading to a high metallic phase content of 82.7% with enhanced electrical conductivity. Together with the expanded interlayer distance (≈1.23 nm), this allows rapid electron transfer and ion transport in the excessively stacked ultrathick MoS 2 film to be simultaneously realized. Thus, the as-fabricated MoS 2 ||graphene/carbon nanotube asymmetric supercapacitor presents both high energy and power densities, outperforms those of commercial devices, including supercapacitors with submillimeter-thick electrodes and even micrometer-thick electrodes.
nanomaterials into submillimeter and even thicker electrodes for practical applications.
The tremendous interest in using MoS 2 as the miniaturized supercapacitor electrodes stems from its high electrochemical activity derived from its variable Mo oxidation states and abun dant active edge S atoms, wellaligned layered structure, and highly accessible surface area. [10,[24][25][26] Although Chhowalla and colleagues [16] have successfully demonstrated a superior volu metric capacitance of ≈700 F cm −3 for micrometer thick MoS 2 , the thickness (5 µm) cannot meet the requirements of indus trial applications. To the best of our knowledge, MoS 2 film at submillimeter thickness with a high volumetric capacitance has not yet been reported, and its commercial application for energy storage is still precluded. Two critical issues need to be addressed in order to achieve the high volumetric capaci tance for MoS 2 , especially at an industriallevel submillimeter thickness: i) the low conductivity, which is strongly limited by its low metallic 1T phase content. Generally, MoS 2 has a 2H phase crystal structure with semiinsulating property and a 1T phase crystal structure with superior electrical conductivity (10 7 times more conductive than that of the semiconducting 2H phase). [10,16,24,27] MoS 2 nanosheets prepared by the conven tional organic lithium intercalation [16,[28][29][30][31] and hydrothermal strategies [32][33][34][35] usually have an 1T phase content less than 70%, leading to poor electron transfer rate, high electrical resistance, and relatively low volumetric capacitance, especially for thick films. Moreover, the metastable 1T phase is easily converted to the stable 2H phase, [36] which significantly restricts the practical applications; ii) the sluggish ion kinetics and few accessible active sites which are intrinsically associated with conventional 2D nanomaterials. Due to the interlayer agglomeration (or the excessive nanosheets stacking in MoS 2 ), thick MoS 2 films inevi tably result in a lengthy ion diffusion path and high transport resistance, declining the utilization of builtin active sites and charge storage capability.
Herein, we report a solvatedionintercalated hydrothermal strategy to simultaneously address the above challenges, achieving a recordhigh volumetric capacitance (511.29 F cm −3 ) for supercapacitors based on submillimeter MoS 2 film elec trode (94.2 µm). In our approach, the solvated lithium interca lation increases the negative charges on the MoS 2 nanosheets, leading to a lowered formation energy for the 1T phase. The metallic 1T phase content of the asfabricated MoS 2 nanosheets thus reaches 82.7% (remains at 72.73% after 60 days), which is significantly higher than that of their counterparts from tra ditional hydrothermal methods, [32][33][34][35]37] and is comparable to those from the chemical vapor deposition (CVD) routes. [38] In addition to the high 1T phase content, the asfabricated MoS 2 nanosheets also show an expanded interlayer spacing (from ≈0.62 to ≈1.23 nm), a rapid electron transfer, and unimpeded ion transport. As a result, the 1.45µmthick and 5.14µmthick MoS 2 films reached volumetric capacitances as high as 1054.5 and 798.5 F cm −3 , respectively. A high volumetric capacitance of 511.29 F cm −3 can still be achieved for the 94.2µmthick MoS 2 film, which is among the best values reported in the literature for submillimeter thick electrodes. [14,18,23,39] The as fabricated MoS 2 ||graphene/carbon nanotube (CNT) asymmetric supercapacitor exhibits both high volumetric energy and power densities of 16.36 mWh cm −3 and 7.5 W cm −3 , respectively, outperformed those of commercial devices, including super capacitors with submillimeterthick electrodes and even micro meterthick electrodes.

Fabrication of MoS 2 with High 1T Phase Content
In this work, we developed a solvatedionintercalated hydro thermal method to fabricate MoS 2 nanosheets. Briefly, solvated lithium ions are introduced as the intercalator during the hydro thermal reaction of ammonium molybdate (Mo source) and thioacetamide (S source) in a Teflonlined stainless autoclave (see Experimental Section). Apart from the inherent advantages of hydrothermal strategies (e.g., easily scaleup, timeeffective, and mild reactions without hazardous organics), [32][33][34] the newly developed method can realize a much higher 1T phase content of MoS 2 (up to 82.7%) with a significantly improved phase sta bility (phase content of 72.3% after 60 days) over traditional hydrothermal methods.
A key feature of the newly developed method is that solvated alkali metal ions (e.g., lithium ions) are intercalated into the interlayer spacing of MoS 2 nanosheets during the hydrothermal reactions. In the traditional hydrothermal processes, 1T MoS 2 nanosheets are generally prepared by Mo source (e.g., ammo nium molybdate and molybdenum trioxide) and S source (e.g., thioacetamide and thiourea) through the reduction reactions induced by the reducibility of the S precursors, as shown in Figure 1a. However, it suffers from a poor reduction rate and limited metallic phase content. Inspired by the reduced for mation energy of 1T phase MoS 2 through introducing alkali metal ions in the CVD processes, [40] we added Li 2 SO 4 solution into the hydrothermal reactions in this work ( Figure 1a). The solvated lithium intercalation can increase the negative charges on MoS 2 nanosheets, leading to lowered formation energy of metallic phase for a high 1T phase content ( Figure 1b). Mean while, the interlayer spacing is expanded after the solvated ion intercalation. The asproposed new method is scalable through a rolling process (see Experimental Section) and aligns well with commercialization, which is demonstrated by a ≈70 cm × 7 cm 1T MoS 2 film with a submillimeter thickness ( Figure 1c).

Material Characterization and Formation Mechanism
Quantitative information of 1T phase content is estimated based on the deconvolution of Xray photoelectron spectroscopy (XPS) peaks. As shown in Figure 2a, the Mo 3d of 1T phase exhibits two strong peaks at 228.0 (Mo 3d 5/2 ) and 231.2 eV (Mo 3d 3/2 ), which are shifted to the lower binding energy (by ≈1.2 eV) in comparison with the 2H phase (229.2 and 232.4 eV, respectively). The corresponding peak deconvolution of Mo 3d reveals the content of the 1T and 2H phase. [35,36,40,41] It is observed that with the increase of Li + concentration, the 2H phase (blue regions in Figure 2a) of the Li + intercalated MoS 2 nanosheets decreases accordingly. In comparison with the tra ditional hydrothermal strategy, the solvated lithium intercala tion remarkably improves the 1T phase content from 65.1% to www.advenergymat.de www.advancedsciencenews.com up to 82.7%, which increases with the increasing Li + concen tration of the precursor solution from 0.5 to 1.5 m. The high metallic phase content is also confirmed by the Raman peaks at 151.28, 216.74, 324.76, and 408.47 cm −1 for 1T MoS 2 nanosheets ( Figure S1, Supporting Information), agreeing well with previ ously reported Raman results. [35,36,38,41] For comparison, the intercalation of 1.5 m solvated Na + and K + is conducted and exhibits 1T phase contents of 75.4% and 70.72%, respectively, which are lower than that of Li + intercalated MoS 2 nanosheets ( Figure S2, Supporting Information). It could be explained that hydrated Li + can carry more water molecules with a higher die lectric constant than that of Na + and K + , leading to more nega tive charges on the MoS 2 nanosheets.
The improved 1T phase content can be attributed to the low ered formation energy of the 1T phase, which is induced by the increased negative charges on the MoS 2 nanosheets after the solvated lithium intercalation. Transmission electron micro scope (TEM) images are used to reveal the successful intercala tion of solvated lithium ions. As shown in Figure 2b, the inter layer spacing of the Li + intercalated MoS 2 nanosheets are 1.04, 1.15, and 1.23 nm, corresponding to the Li + concentrations of 0.5, 1, and 1.5 m, respectively, which are higher than those of MoS 2 nanosheets prepared from the traditional hydrothermal method (0.88 nm) and the typical value of closely packed MoS 2 (≈0.62 nm). [29] Xray diffraction (XRD) measurements are performed to determine the interlayer spacing of the MoS 2 nanosheets. Compared to MoS 2 nanosheets from the traditional hydrothermal method, the XRD pattern of Li + intercalated MoS 2 nanosheets shows a similar (002) peak at ≈14° and an additional (001) peak at ≈7.3°, which are associated with inter layer spacing of ≈0.63 and ≈1.21 nm, respectively ( Figure S3, Supporting Information). The presence of (001) peak indicates the expansion of the interlayer spacing after the intercalation of solvated lithium ions. Moreover, the existence of solvated lithium ions is also proved by the XPS peak of Li + ( Figure S4, Supporting Information). Zeta potential measurements are performed to investigate the change of negative charges on the MoS 2 nanosheets after the intercalation of solvated lithium ions. The average zeta potential of MoS 2 nanosheets from the solvatedionintercalation method (1.5 m Li + ions) is −38.1 mV, which is higher than that of MoS 2 nanosheets (−32.0 mV) from the traditional hydrothermal strategy (Figure 2c). These results reveal that the solvated lithium intercalation can increase the amount of negative charges on the MoS 2 nanosheets.
Density functional theory (DFT) calculations are performed to reveal the influence of negative charges on the formation energy of the 1T phase. Spinpolarized DFT calculations are conducted with generalized gradient approximation [42] based on the Perdew-Burke-Ernzerhof [43] functions. The energy and force convergence criteria are set to 1 × 10 −5 eV and 1 × 10 −2 eV/Å, respectively, with an energy cutoff of 400 eV (see Experimental Section). Figure 2d shows the 4 × 4 super cells of 1T and 2H phase MoS 2 structures for the DFT calculations. The optimized geometric structures are consistent with the previous simulation studies. [44] As shown in Figure 2e, the dif ference in the formation energy between 1T and 2H phases of MoS 2 decreases from 13.48 to −4.47 eV with increasing surface charge density, indicating that the formation of 1T phase MoS 2 becomes easier than that of 2H phase after the solvated lithium intercalation, which is probably attributed to the electron filling of the d orbits of Mo atoms. [36] Since the metastable 1T phase is easily converted into the 2H phase, [36,45] the phase stability of 1T MoS 2 nanosheets is another critical issue for real applications. As shown in Figure 2f and  Figure S5, Supporting Information, the 1T phase content of the Li + intercalated MoS 2 nanosheets decreases from 82.7% to 72.6% with a high retention ratio of 87.8%, and the corre sponding aqueous dispersion remains stable without obvious precipitation after 60 days. In contrast, the phase content of samples made from the traditional hydrothermal method decays significantly (1T phase content from 65.1% to 51.6% after 60 days with a retention ratio of 79.3%). Meanwhile, particle precipitation can be easily seen after the first 24 h ( Figure S6, Supporting Information), due to the severe restacking of 2H MoS 2 nanosheets with poor wettability. [33]

Submillimeter-Thick MoS 2 Film with High Volumetric Capacitance
The high metallic 1T phase content and expanded interlayer spacing could facilitate fast electron transfer and rapid ion transport, as demonstrated by the excellent volumetric capaci tive performance for micrometer and submillimeterthick MoS 2 films. As shown in Figure 3a- (Figure 3d, solid lines), the capacitance C consists of two con tributions (C = k 1 + k 2 v −0.5 ), [46] that is, rateindependent compo nent k 1 (surface capacitive effects, Figure 3d, dashed lines) and diffusionlimited capacitance k 2 dependent on the scan rate ν. The Li + intercalated MoS 2 film shows substantially high sur face capacitive contributions (≈85.2%), superior to its counter part from the traditional hydrothermal method (≈57.5%). These results indicate better accessibility to the active sites of MoS 2 nanosheets with an expanded interlayer spacing and high 1T phase content. Moreover, CV profiles can be obtained at a high scan rate of 1000 mV s −1 , and the ideal capacitive behavior with a Columbic efficiency of 98.2% is further confirmed by galva nostatic charge/discharge (GCD) curves at the current den sities up to 600 A cm −3 ( Figure S7, Supporting Information). The electrochemical impedance spectroscopy (EIS) for the Li + intercalated MoS 2 film confirmed the reduced equivalent series resistance (R s ) and negligible charge transfer resistance (R ct ). The equivalent circuit fitting results ( Figure S9, Sup porting Information) show that the R ct and R s are 0.45 and 0.78 Ω cm 2 , respectively, which are significantly lower than those of the MoS 2 film from the traditional hydrothermal method (3.45 and 2.94 Ω cm 2 , respectively). As a result, the Li + intercalated MoS 2 film presents a much higher volumetric capacitance of 1054.5 F cm −3 (at a scan rate of 5 mV s −1 ) with improved rate performance ( Figure S10, Supporting Information). The Li + intercalated MoS 2 film also shows a high volumetric capacitance of 536.2 F cm −3 at a high scan rate of 1000 mV s −1 , which is sub stantially higher than that of the counterpart from the traditional hydrothermal method (72.59 F cm −3 at 1000 mV s −1 ).
In general, the increase in film thickness causes sluggish ion diffusion and reduces charge storage capability, resulting in a significant decrease in the volumetric capacitance. [2,22] In this work, however, the excellent volumetric capacitive performance is almost completely retained for a thicker Li + intercalated MoS 2 film (5.14 µm, Figure 3b). As shown in Figure 3e and Figure S11, Supporting Information, the 5.14µmthick MoS 2 film exhibits a slightly declined volumetric capacitance (798.5 F cm −3 ) as compared to the 1.45µmthick film. Moreover, the volumetric capacitance of our 5.14µmthick film is largely superior to the previously reported 5µmthick 1T MoS 2 film prepared by the organolithium chemistry method. [16] Besides, the capacitance retention from 5 to 1000 mV s −1 of our 5.14µmthick film is 46.4%, which is much higher than that of the sample from the traditional organic chemistry method (14.4%).

Submillimeter-Thick MoS 2 Film Supercapacitor
To demonstrate the potential practical applications, an asym metric MoS 2 ||graphene/CNT supercapacitor is fabricated with submillimeterthick MoS 2 film and graphene/CNT film as the anode and the cathode, respectively, 1.0 m Li 2 SO 4 as the elec trolyte, and a glass fiber as the separator (Figure 4a). The GCD curves from 0.1 to 2 A cm −3 and the CV curves are presented in Figure 4b and Figure S13a, Supporting Information, respec tively, exhibiting a high Columbic efficiency of 95.0%. As shown in Figure 4b, the asymmetric supercapacitor exhibits a volumetric capacitance of 52.4 F cm −3 at 0.1 A cm −3 . According to the EIS tests ( Figure S13b, Supporting Information), the www.advenergymat.de www.advancedsciencenews.com asymmetric supercapacitor shows typical capacitive character istics. Ragone plot in Figure 4c shows a comparison of the vol umetric energy and power densities between our device and previous studies. At a current density of 0.1 A cm −3 , the volu metric energy density is calculated to be 16.36 mWh cm −3 with the corresponding volumetric power density of 0.075 W cm −3 . At a higher current density of 10 A cm −3 , our device shows a volumetric energy density of 5.36 mWh cm −3 and a volumetric power density of 7.5 W cm −3 . These results outperform the commercially available devices (e.g., 4 V/500 µAh Li thinfilm battery; [48] 3 V/300 µF electrolytic capacitor; [13] 2.75 V/44 mF and 5.5 V/100 mF commercial supercapacitors [13,49] ), as well as supercapacitors with submillimeterthick electrodes (e.g., ≈150 µm activated carbon fibers, [19] ≈39 µm reduced graphene oxide (GO)/CNT electrode, [50] ≈20 µm MXene paper elec trode, [51] and ≈18 µm porous carbon electrode [52] ) and some micrometerthick electrodes (e.g., 2.5µmthick MXene/gra phene, [53] 0.58µmthick reduced graphene, [54] and 3µmthick MoS 2 /reduced graphene [33] ). Moreover, our device exhibits high capacitance retention of 92.2% after 12 000 charge/dis charge cycles at a current density of 5 A cm −3 , demonstrating excellent cyclic stability (Figure 4d). The outstanding perfor mances can be attributed to the rapid electron transfer and unimpeded ion transport induced by the expanded interlayer spacing and high 1T phase content after solvated lithium intercalation.

Conclusion
We have demonstrated a solvatedionintercalated hydrothermal strategy to prepare MoS 2 nanosheets with a high metallic 1T phase content, which are promising for the preparation of industriallevel submillimeter MoS 2 films with high volumetric capacitance. The solvated Li + ion not only expanded the inter layer spacing of MoS 2 nanosheets but also increased the nega tive charges on the MoS 2 nanosheets and reduced the formation energy of the 1T phase, leading to the fast electron transfer and ion transport for submillimeter MoS 2 films. Benefiting from these advantages, high volumetric and areal capacitances of 511.29 F cm −3 and 4.82 F cm −2 can still be achieved, which is among the best records reported for submillimeterthick elec trodes. The asfabricated MoS 2 ||graphene/CNT asymmetric supercapacitor exhibits high volumetric energy and power den sities of 16.36 mWh cm −3 and 7.5 W cm −3 , respectively, as well as good cycling stability with capacitance retention of 92.2%

Experimental Section
Preparation of 1T MoS 2 by the Solvated-Ion-Intercalated Strategy and the Traditional Hydrothermal Strategy: To prepare the pristine 1T MoS 2 samples by the traditional hydrothermal strategy, ammonium molybdate (25 mg, Shanghai Macklin Biochemical LTD), thioacetamide (30 mg, Shanghai Macklin Biochemical LTD), and urea (100 mg, Sinopharm Chemical Reagent LTD) were mixed in deionized water (25 mL) followed by 2 h magnetic stirring at 600 rpm. Then, the mixed solution was transferred into a Teflon-lined stainless autoclave and kept in a furnace at 180°C for 18 h. Subsequently, the autoclave was cooled down to room temperature rapidly by continuous water flow, and then further stabilized at 4 °C for 2 h. The as-prepared samples were collected after centrifugation and washing with deionized water and ethanol for several times, which removed the relatively large nanoparticles and retained the few-layer nanosheets in the MoS 2 dispersion. After 30 min ultrasonic treatment, the 1T MoS 2 samples were stably dispersed in deionized water and kept at a 4°C environment for long-term storage. To prepare Li +intercalated 1T MoS 2 samples, lithium sulfate (0.275, 0.550, and 0.825 g, Shanghai Aladdin Biochemical Technology LTD) was added into the wellmixed precursor solution mentioned above, which was continuously to stir at 600 rpm for another 0.5 h. Therefore, the concentration of Li + ion in the mixed precursor was 0.5, 1.0, and 1.5 m. The yield of the 1T MoS 2 samples increased proportionally by scaling up the reaction volume.
Material Characterization: The microstructures of samples were characterized by scanning electron microscope (SEM) (Hitachi SU-70) and TEM (JEOL JEM-2100). Raman spectra were measured by a Raman spectrometer (LabRAM HR Evolution) with a 532 nm excitation wavelength. The XRD characterization was conducted on an X-ray diffractometer (Bruker AXS-D8) with Cu/Ka radiation (λ = 1.5406 Å). XPS (Escalab Mark II, VG) with a monochromatic Mg Ka X-ray source (1253.6 eV) was used to obtain XPS data. To identify the ratios of 1T and 2H phases of the MoS 2 nanosheets, the 1T and 2H deconvoluted peaks of Mo 3d were fitted, and the areas of the corresponding peaks can be obtained, respectively. The area ratio of the corresponding peaks represents the ratio of 1T and 2H phases, and the 1T phase content can be calculated by the formula: where C 1T represents the 1T phase content, S 1T and S 2H represent the areas of the 1T and 2H peaks, respectively. Before Raman, XPS, and XRD characterizations, the 1T MoS 2 dispersion was drop casted on a quartz plate and dried naturally at room temperature. The specific surface areas of the prepared film electrodes were characterized by N 2 adsorption-desorption isotherms at 77.4 K using a surface area analyzer (Quantachrome, AUTOSORB-1-C). Density Functional Theory Calculations: The relative stability of 1T and 2H MoS 2 was obtained from DFT simulations, performed using Vienna ab initio simulation package (VASP) [55,56] with generalized gradient approximation [42] based on Perdew-Burke-Ernzerhof [43] functions. The energy and force convergence criteria were set to 1 × 10 −5 eV and 1 × 10 −2 eV/Å, respectively, with an energy cutoff of 400 eV. A k-point mesh of 5 × 5 × 1 was applied to the Brillouin zone within Monkhorst− Pack grids. The relative stability of 1T MoS 2 compared to 2H MoS 2 (E s (c)) was calculated using where E T (c) and E H (c) represent the total energy of 1T and 2H MoS 2 with lithium adsorbed, and c is the surface charge density. Preparation of MoS 2 Electrodes and Asymmetric Supercapacitor: To prepare thin-film electrodes, 1T MoS 2 dispersion was filtered over membranes (25 nm-diameter pore size) and peeled off after drying at 50 °C. The film thickness varied from ≈1 to 10 µm depending on the amount of filtered dispersion. To prepare submillimeter-thick film electrodes, the MoS 2 dispersion was freeze-dried to obtain 1T MoS 2 powder. It was worth noting that when the freeze-dried ice just completed the sublimation, the remaining powder was collected immediately to avoid the loss of water molecules between the MoS 2 nanosheets. After manually stirring the mixture of 1T MoS 2 powder and PTFE with a ratio of 9: 1 for over 3 h, the well-mixed slurry was rolled, freeze-dried, and pressed into film electrodes with a thickness of 94.2 µm and a density of ≈2.5 g cm −3 . The freeze-drying process formed sufficient pores for the penetration of electrolytes and prevented the phase conversion of MoS 2 nanosheets from 1T to 2H phase. XRD patterns revealed that the interlayer spacing of the filtrated and rolled MoS 2 films was ≈1.21 nm and ≈1.09 nm, respectively ( Figure S14, Supporting Information). The slightly decreasing interlayer spacing of the rolled MoS 2 films was due to the partial loss of water molecules during the freeze-drying process. Note that an interlayer spacing of ≈0.62 nm also existed in the filtrated and rolled MoS 2 films according to the XRD patterns, which indicated that solvated Li + ions cannot be intercalated into each layer of MoS 2 nanosheets. The incompletely expanded interlayer spacing was conducive to a high density of 2.5 g cm −3 for the rolled MoS 2 film. The specific surface areas of the filtrated and rolled films were around 8.3 and 5.1 m 2 g −1 , respectively. Besides, the electrochemical performance of filtrated and rolled films at a similar thickness was also measured to rule out the effect of macroporous structure ( Figure S15,S16, Supporting Information). For the preparation of asymmetric MoS 2 ||graphene/CNT supercapacitor, a single-walled carbon nanotube (SWCNT) was used as the conducting agent. Although it was not effective in promoting capacitance values of the as-fabricated supercapacitor, it could significantly improve the cycle stability due to its high conductivity and stable nanochannel structure. 1T MoS 2 dispersion was first mixed and stirred with SWCNT dispersion with an active substance mass ratio of 8: 2. Then the well-mixed dispersion was freeze-dried to obtain mixture powder. Through adding a small amount of water and PTFE (10% of the mixture powder mass), the MoS 2 electrode was prepared by rolling, freeze-drying, and pressing the mixture powder into ≈100 µm film with a high compaction density. To prepare the counter-electrode, GO dispersion (10 mg mL −1 ) was synthesized by a modified Hummers' method. The well-sonicated mixture of 8 mL GO dispersion, 20 mg CNT, and 10 mg ascorbic acid was sealed into a stainless steel autoclave and heated at 65°C for 3 h and 70°C for 1 h to obtain graphene/CNT hydrogel. Graphene/CNT aerogel was obtained after freeze-drying at −80 °C. The counter electrode was obtained by pressing the aerogel into stacked graphene/CNT film with a film thickness of ≈140 µm and a density of ≈0.74 g cm −3 . The asymmetric supercapacitor was assembled by stacking and pressing 22-µm-thick aluminum foil (collectors), MoS 2 electrode (anode), graphene/CNT electrode (cathode), and glass fiber separator into a button supercapacitor cell. The mass loading of the anode and cathode was around 15.1 and 10.4 mg cm −2 , respectively, which were adjusted based on the comprehensive matching of charge balance and electrode thickness. Moreover, an asymmetric MoS 2 ||activate carbon supercapacitor was assembled using industrial-level activated carbon as the cathode, which also exhibited excellent volumetric performance ( Figure S17, Supporting Information).
Electrochemical Measurements: Electrochemical measurements were carried out in a three-electrode configuration using an electrochemical workstation (PGSTAT302N, Metrohm Autolab B.V.). Ag/AgCl electrodes and activated carbon were used as reference and counter electrodes, respectively. In order to make the comparison more convincing, the thickness and quality of the tested electrodes were normalized. During the three-electrode tests, CV data were obtained at the voltage windows between −1 and 0.2 V versus Ag/AgCl with the scan rates ranging from 5 to 1000 mV s −1 . For the asymmetric supercapacitor, the effective working voltage was chosen at 0-1.5 V with the scan rates of 1-100 mV s -1 . Before the electrochemical measurements, the volume of electrodes was calculated by the measured thickness and area.
The specific volumetric capacitances (C v , F cm −3 ) were calculated by the following formula where I represents the volume normalized current (A cm −3 ), t is the discharge time (s) obtained in GCD measurements, and V is the voltage window (V). The energy and power densities of the supercapacitor were calculated by the following formula where C cell (F cm −3 ) is the total volumetric capacitance of the asymmetric electrode cell, V cell (V) is the effective working voltage of the discharging process, t cell (s) is the discharging time, E v and P v are specific volumetric energy and power density, respectively.

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.