Cost-effective conversion of “stones” into high-performance capacitor carbon through a solid–solid inorganic chemical reaction

Abstract

Supercapacitors are highly sought after by the expanding new energy industry owing to their advantages of high power and long life. However, porous carbon, a crucial electrode material, is extremely expensive. As a result, the supercapacitor manufacturing industry has developed a strong demand for a new, low-cost method for synthesizing capacitor carbon. This study reports for the first time a novel method for producing high-performance capacitive carbon from ultra-low-cost raw materials CaCO₃ (the primary stone component) and CaC₂ (also referred to as electrical stone), which is accomplished via ball milling the two materials to facilitate a solid–solid inorganic chemical reaction. The specific surface area attained by this approach reaches 1000 m² g⁻¹ because of the template function of CaO generated in situ during the reaction, which is the highest value reported to date for CaC₂-derived carbon. The as-prepared capacitive carbon performed well in both aqueous and organic electrolytes, with a coulombic efficiency of approximately 100%. It outperforms the commercial capacitive carbon YP50F, even when prepared on a kilogram scale. This advancement dramatically reduces the cost associated with the large-scale production of porous carbon for supercapacitors, thus establishing a long-term relationship between carbon neutrality and clean energy development.

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Introduction

Global warming caused by CO₂ emissions has become a public problem.¹ In response, the vigorous development of clean energy, low-carbon industries, and green transportation has become a trend. Among such developments, the demand for electrochemical energy-storage devices, such as Li-ion batteries and supercapacitors (SCs), has reached an all-time high and continues to grow, making them an important driver for advancing the goal of carbon neutrality.^2,3 In addition to reducing CO₂ emissions, converting CO₂ into useful substances/materials is an important direction,⁴e.g. converting it into stone (i.e., CaCO₃) through mineralization or into organic compounds via plants in nature.^5–7 In fact, a variety of CO₂-conversion products, such as methanol, acetic acid, and other high value-added products, have been demonstrated to have practical use.⁸ However, the conversion of CO₂ into nanocarbon materials, especially electrode materials suitable for electrochemical energy-storage devices (e.g., high-performance porous carbon for SCs), is rarely reported.

Ideally, porous carbon for SCs usually requires a high specific surface area (SSA) and conductivity.⁹ However, the SSA of porous carbon obtained through preparation strategies based on a high-temperature reduction of CO₂ by reducing agents is still at a low level (<700 m² g⁻¹),^10–12 far below the expectation of at least 1000 m² g⁻¹. Moreover, feedstock CO₂ is still mainly based on compressed cylinder gas obtained after purification, rather than on CO₂ directly emitted by industries, which limits the practicality of the method.^2,13,14 In fact, the main route to carbon neutrality is still dominated by the solidification of CO₂ (i.e., converting CO₂ into CaCO₃, which is widely available in nature in the form of stones).¹⁴ Accordingly, it would be of great practical value and significance if stones could be converted into high value-added porous carbon electrode materials under mild conditions.

Herein, a new strategy for the preparation of high-specific-surface-area capacitive carbon from low-cost CaCO₃ (i.e., the main constituent of stones) and CaC₂ (i.e. commonly known as electrical stone) by utilizing the solid–solid inorganic chemical reaction induced by ball milling is reported for the first time. The only by-product obtained was CaO. Further, the template effect of CaO endowed the resulting template carbon (TC) with SSA >1000 m² g⁻¹ and enabled it to exhibit a high gravimetric capacitance (C_wt) and rate performances beyond those of commercial capacitive carbon.^15–17 Compared with the traditional synthesis method of the gas–solid reaction at high temperature, this strategy involves a solid–solid reaction under mild conditions, which not only consumes less energy but is also easier for industrialized production. The strategy offers advantages of simplicity and scalability, but there are still some constraints too: (i) the purity or impurity problems of the raw materials, e.g., CaC₂, which are often accompanied by SiC impurities; (ii) the consumption of large amounts of the energy-intensive raw material CaC₂ is not conducive to carbon neutrality; (iii) the large ball milling equipment required for scaled-up increases the production cost, as well as generates large dust and noise pollution.

Experimental section

Preparation of TC

Calcium carbide (CaC₂, 98%) and calcium carbonate (CaCO₃, 99%) were purchased from Sinopharm Chemical Reagent Co., Ltd. All the chemicals were of analytical grade and did not require further purification for use. The reaction of CaC₂ and CaCO₃ was carried out in a planetary ball mill (MSK-SFM-1S, Hefei Kejing, China) at room temperature according to the stoichiometric ratio of the reactants. CaC₂ was first ground in the planetary ball mill for 5 min before use, and then was uniformly mixed with CaCO₃ powder for the reaction. For example, 1.2 g of CaC₂, 1 g of CaCO₃ powder, and a certain mass of stainless-steel balls (ball/material mass ratio of 20 : 1) were added to the reactor, which was sealed and fixed. The rotational speed of the ball mill was 100 rpm with a 2 min interval every 30 min for a cumulative ball milling time of 4 h. After the ball milling, the mixed C@CaO product was annealed in a tube furnace at 5 °C min⁻¹ to 700 °C and held there for 2 h. The product was treated with dilute HCl to remove all the residual reactants, washed with distilled water to pH 7, and finally the filter cake was dried under vacuum at 120 °C for 5 h to obtain the TC.

The procedure for the preparation of kilograms of the TC material was essentially the same as the method described above, except that the speed of the ball milling was increased to 300 rpm, and larger-diameter ball milling beads were also selected. After the ball milling reaction, the mixed product was washed with acid and water and dried to obtain kilograms of TC (i.e., TC_1kg).

Measurement of the electrochemical performance of TC

The electrochemical properties of the TC were measured in a two-electrode configuration. Standard electrode preparation method was used, i.e., 85 wt% TC (1.0 mg), 10 wt% acetylene black, and 5 wt% PTFE were mixed in an agate mortar with a small amount of ethanol solvent to form a mortar, stirred with a mortar stick, and coated onto slides to form uniformly thick circular disks that were pressed onto the surface of nickel foam collectors to form electrodes. Finally, they were dried in a vacuum oven at 120 °C for 10 h to completely remove ethanol. Each group of TC electrodes was packed in a CR2032 battery box, which was separated by a separator; further, the aqueous electrolyte was 6.0 mol L⁻¹ KOH/H₂O, while the organic electrolyte was tetraethylammonium tetrafluoroborate/acetonitrile (1.0 mol L⁻¹ Et₄NBF₄/AN). The current collectors were made of foamed nickel with a clean and flat surface. The electrochemical properties of the commercial electrode material YP50F were tested using the same method as described above.

An electrochemical workstation (IVIUM, Vertex One-C) was used to perform cyclic voltammetry (CV) measurements at different scan rates and to obtain galvanostatic charge/discharge (GCD) curves at different current densities. The voltage window was set at 0–1 V in KOH/H₂O and 0–2.7 V in Et₄NBF₄/AN, respectively. Electrochemical impedance spectroscopy was performed with 10 mV amplitude sinusoidal signals in the frequency range of 100 kHz to 10 mHz.

The gravimetric capacitance (C_wt, F g⁻¹) of the TC was calculated from the GCD curve using eqn (1):

C_wt = 2 (I × Δt)/(m × ΔU) (1)

where I (A) is the constant discharge current, Δt (s) is the time of total discharge, m (g) is the mass of the TC on one electrode, and ΔU (V) represents the working voltage windows (i.e., excluding the voltage drop). The gravimetric energy density (E_wt, Wh kg⁻¹) was calculated using eqn (2):

E_wt = C_wt (ΔU)²/(2 × 4 × 3.6) (2)

The corresponding gravimetric power density (P_wt, W kg⁻¹) was obtained from eqn (3):

P_wt = 3600 × E_wt/Δt (3)

where R_ESR is the DC equivalent series resistance, which was obtained by the constant-current charging and discharging method and V_drop is the voltage drop at a discharge current of I, as shown in eqn (4):

R_ESR = V_drop/2I (4)

General characterization

The morphologies of the materials, such as the TC, were analyzed by scanning electron microscopy (SEM, JSM-7800F). Here, a small amount of material was dispersed on a conductive adhesive by dipping a toothpick into the material; the accelerating voltage used was 12 kV. The voltage for the transmission electron microscopy (TEM, JEM-2100) analysis was 20 kV; and the samples were prepared by adding the material to a suitable amount of ethanol reagent, and then dispersing the material by ultrasonication, followed by taking a little drop of the liquid on a copper grid, and then drying it with an infrared lamp. Al Kα was used as the irradiation target for the XPS measurement; the corresponding operating voltage and power were 12 kV and 72 W. The binding energy (BE) range for the XPS wide scans was 1361 to 0 eV, with a band step of 1 eV, while that of the XPS narrow scans was in the range of 550 to 0 eV; and in the narrow scans, the C 1s and O 1s regions were acquired with a step of 0.1 eV. For background subtraction, linear subtraction was used in all cases. Peaks were fitted with Lorentz–Gaussian functions. The specific surface area (SSA) was calculated using the Brunauer–Emmett–Teller (BET) method. Samples were degassed at 300 °C for 6 h before being measured. The method is based on adsorption data in the p/p₀ range of 0.05 to 0.3. The Horvath–Kawazoe (HK) method was used for micropores (<2 nm) and the Barrett–Joyner–Halenda (BJH) method for mesopores (2–50 nm) to calculate the pore-size distribution based on the corresponding adsorption branch of the N₂ isotherms. X-Ray diffraction (XRD, Bruker D8) and Raman spectroscopy (Lab RAM Aramis, 532 nm laser excitation) were used to characterize the structure and composition of the samples.

Results and discussion

Fig. 1 shows the preparation and structure of the TC. The preparation of the TC involved the solid–solid chemical reaction of CaCO₃ and CaC₂ in the presence of ball milling (Fig. 1a),^18,19 and then the product (i.e., C@CaO) was treated with dilute acid to obtain the TC. C@CaO exhibits a distinctly different XRD pattern from CaCO₃ and CaC₂ (Fig. 1b); its characteristic diffraction peaks (200) at 32.1°, (211) at 37.5°, and (400) at 54.5° are attributed to cubic CaO, suggesting that Ca²⁺ species were transformed into CaO.²⁰ Compared with C@CaO, the intensities of the characteristic diffraction peaks (002) at 24.49° and (101) at 45.21° of TC are significantly enhanced. The two sharp diffraction peaks at 35° and 60° arise from the impurity SiC in the raw material CaC₂, but its content is very low, only about 0.98% (as indicated by the XPS result in Fig. S1, ESI†). It was difficult to be removed by strong acids or bases (Fig. S2, ESI†), proving its chemically inert nature. Also, due to its high chemical stability and very low content, it had little effect on the capacitive performance of the TC. The peak positions of the TC are almost consistent with those of commercial YP50F, indicating that the obtained TC is indeed a C-dominated porous carbon material.^21,22 This is also verified by the IR and Raman results (Fig. S3, ESI†).²³ Collision/friction in ball milling allows the reactants to gain enough activation energy to break chemical bonds while increase the dispersion of the products with porous morphology.^21,24,25 As a result, the TC obtained here is in the form of particles with a size in the range of 1–5 μm (Fig. 1c and d). The particles have a hollow structure rather than a solid one, as observed in the high-magnification TEM images (Fig. 1e), suggesting an abundant micro/mesoporous structure. The pore structures are closely related to the template function of CaO, which was removed by dilute acid in C@CaO. In addition, the rearrangement and irregular cross-linking of carbon chains under high-intensity mechanical force play an important role in the formation of the porous structure and abundant ion-adsorption sites for TC.¹⁸ This is further confirmed by the following results for the N₂ adsorption/desorption isotherms.^17,26

Fig. 1 Preparation and characterization of TC. (a) Typical schematic of the preparation process and main principle; (b) XRD patterns; the data for the raw materials (i.e., CaC₂ and CaCO₃), intermediates and YP50F are provided for comparison; (c and d) SEM images with different magnifications; (e) TEM image.

Fig. 2 illustrates the pore structure characterization of the TC. It demonstrates a Brunauer–Emmett–Teller SSA of 1090 m² g⁻¹, which is higher than that (<700 m² g⁻¹) of the reported porous carbon using CO₂ as a direct feedstock.¹⁰ The N₂ adsorption/desorption isotherm displays a hysteresis loop at 0.5 < p/p₀ < 0.97 (Fig. 2a), indicating the predominant presence of mesopores.^27–30 In contrast, the isotherm of YP50F displays an I-type curve, i.e., there is no significant hysteresis loop, indicating that the material is predominantly microporous and had strong interactions with N₂.^31,32 The TC not only contains a large number of 0.7–1.7 nm micropores as in YP50F, but also has a large number of mesopores with pore sizes in the range of 5–30 nm (Fig. 2b), implying that the TC may have higher rate performance in SCs than YP50F due to the presence of mesopores.³³ Accordingly, they have similar micropore volumes (0.18 vs. 0.56 cm³ g⁻¹), but the mesopore volume is much larger than that of YP50F (1.24 vs. 0.08 cm³ g⁻¹), as shown in Fig. 2c. The above results indicate that there are not only a large number of pores smaller than 2 nm, but also a large number of mesopores of 8 nm in the TC samples; whereby the former dramatically enhances the SSA of TC, which would allow for the adsorption/desorption of more ionic charges, while the latter would provide fast diffusion channels and shorter diffusion distances for the ions.³⁴ This facilitates the improvement of the capacity of TC-based SCs under high-rate charging/discharging conditions.

Fig. 2 Pore structure and composition characterizations of the TC. (a) N₂ adsorption/desorption isotherms; (b) pore-size distributions; (c) pore volumes of micropores and mesopores; (d) full XPS spectra; (e and f) corresponding fine spectra of C 1s and O 1s. For comparison, the data of YP50F are provided.

Both TC and commercial YP50F contain a certain amount of O species (10.55% vs. 12.66%), but the one in TC is slightly lower, as shown in the full spectrum of XPS in Fig. 2d. Similar to YP50F, all the O species in TC are present as C–O, C=O, and O–C=O (Fig. 2e and f),¹⁸ confirming the presence of oxygen-containing groups on the surface. Oxygen-containing functional groups are beneficial in providing part of the capacity of the active material through reversible redox reactions, especially in aqueous electrolyte systems (e.g., typical 6.0 mol L⁻¹ KOH/H₂O).³⁵ The C_wt is theoretically proportional to the SSA, but in practice if the SSA exceeds a critical value, its increase slows down very quickly and approaches its limit (i.e., even if the SSA increases significantly, its capacity would not increase proportionally).^36,37 TC had an SSA greater than 1000 m² g⁻¹, exceeding that of the comparable CaC₂-derived carbon. This implies that in combination with its good affinity to the electrolyte and the capacity contribution of some of the oxygen-containing functional groups, TC may have a higher C_wt performance, as highlighted below.

Fig. 3 shows the electrochemical performance of TC aqueous (6.0 mol L⁻¹ KOH/H₂O) and commercial organic (1.0 mol L⁻¹ tetraethylammonium tetrafluoroborate/acetonitrile, Et₄NBF₄/AN) electrolytes. Two typical electrolytes were used for the evaluation of the TC capacitor performance.⁹ The CV curves at 100 mV s⁻¹ show that TC can achieve voltage windows of 1.0 and 2.7 V in typical aqueous and organic electrolytes, respectively (Fig. 3a and Fig. S4, ESI†).^9,38 The CV curves of TC in Et₄NBF₄/AN were closer to a rectangular shape compared to those in KOH/H₂O, suggesting that the oxygen-containing functional groups on TC were more stabilized in Et₄NBF₄/AN.^39,40 The corresponding C_wt is slightly lower than that in KOH/H₂O, probably due to the contribution of the oxygen-containing functional groups.^41,42

Fig. 3 Electrochemical performance of symmetrical SCs using TC electrodes in 6.0 mol L⁻¹ KOH/H₂O and 1.0 mol L⁻¹ Et₄NBF₄/AN. (a) CV curves at 100 mV s⁻¹; (b) GCD curves at 1 A g⁻¹ and 50 A g⁻¹; (c) C_wt at different current densities; (d) Nyquist plots; the inset is the magnified high-frequency part; (e and f) corresponding evolution of R_ESR against current density and Bode plots. The data for YP50F are provided for comparison.

The GCD curves of the TC at 1 A g⁻¹ in both electrolytes show almost no voltage drop in the shape of an isosceles triangle (Fig. 3b), indicating a more desirable electric double-layer behavior within the voltage window.^32,43,44 At a higher current density of 50 A g⁻¹, they exhibit voltage drops of 0.34 and 0.39 V, respectively, due to the presence of more mesopores, which are both significantly lower than the performances of YP50F (0.45 and 0.64 V). Due to the decrease in conductivity after going from the aqueous system to the organic electrolyte, the voltage drop becomes more pronounced.³⁹ The maximum C_wt values of the TC with KOH/H₂O and Et₄NBF₄/AN are 127 F g⁻¹ and 107 F g⁻¹ (Fig. 3c), respectively, which are both higher than those for YP50F; even when the current density was increased to 20 A g⁻¹ and 50 A g⁻¹, respectively, the corresponding C_wt retention is still higher than 79% (101 F g⁻¹) and 67% (71 F g⁻¹). Although some of the carbons have a higher SSA and C_wt than TC, most of this is due to the contribution of N or B doping. Compared to the most similar CaC₂-derived carbon, TC shows the highest level in terms of both the specific surface area and specific capacitance. Even when compared to CaCO₃-derived carbon, it is still at a leading level (Table S1, ESI†). This result indicates that TC is superior to commercial activated carbon both in terms of capacity and its rate performance.⁴³

The difference in performance between TC and YP50F in aqueous electrolyte was further revealed through Nyquist plots. In the low-frequency section, the curve of TC is almost perpendicular to the real axis X (Fig. 3d), indicating its more ideal capacitive characteristics.^18,32,39 As expected, the R_ESR (2.82 Ω) of TC is significantly smaller than that (5.47 Ω) of YP50F in the high-frequency part (Table S2, ESI†).⁴⁵ It is known, R_ESR consists of Ohmic resistance (R_s), charge-transfer resistance (R_ct), and Warburg diffusion resistance (R_w). TC possesses a smaller R_ESR than YP50F, indicating its lower charge-transfer resistance and more efficient electrolyte diffusion during charging and discharging.³⁹ These could be mainly attributed to the smaller R_ct (0.67 Ω vs. 2.44 Ω) and R_w (1.88 Ω vs. 2.82 Ω) for TC.^46,47 The same trend is exhibited for the DC case (R_ESR) and time constant τ₀ for TC.^48,49 The micropores in the carbon structure may be partially blocked when increasing the current density from 1 to 100 A g⁻¹, while the mesopores and/or macropores could still allow the smooth transfer of the ions involved. When the current density increased to a certain level, the diffusion of ions became difficult;^39,50 while there is a slight tendency toward an increase at the high current density side in the curves of R_ESR plotted against the current density (Fig. 3e), accordingly. However, the R_ESR in the whole range of 1–100 A g⁻¹ is obviously smaller than those of YP50F, demonstrating the low transfer resistance in TC due to its rich mesopore structure. In addition, the time constant τ₀ (τ₀ = 1/f₀, where f₀ denotes the eigenfrequency with a phase angle of −45°) of the TC is 0.16 s, which is significantly smaller than that of YP50F (1.2 s, Fig. 3f), confirming the high-rate performance of the TC.

Fig. 4 demonstrates the electrochemical properties of the TC (TC_1kg) prepared by the ball milling method in the kilogram scale. In the organic electrolyte, the CV curve almost overlaps with that of TC, which shows that the TC_1kg has an ideal capacitive performance, little different from the TC (Fig. 4a). A similar trend is also reflected in their GCD curves. The curve for TC_1kg at 1 A g⁻¹ is almost the same as that of TC (i.e., similar shape and the same 2.7 V voltage window); only the charge/discharge duration is slightly shorter (Fig. 4b), indicating that TC_1kg has a comparable capacity and rate performance to TC. This also suggests that the scaled-up preparation technique for TC proposed in this study is feasible. TC and TC_1kg are similar in structure and morphology, both being granular. However, the average particle-size distribution of TC is only 0.74 μm, whereas that of TC_1kg reaches 2.3 μm (Fig. S5, ESI†). Obviously, the larger particle size of TC_1kg may lead to a slight decay of the performance due to its unfavorable increase in SSA. This difference may be due to the scaling-up effect of the kg-scale ball milling equipment. Further, the AC electrochemical impedance results in organic electrolyte also show that the difference between TC_1kg and TC is very small (Fig. 4c), i.e., both the R_ESR (6.03 Ω vs. 4.30 Ω) and charge-transfer resistance (0.69 Ω vs. 0.64 Ω) values were very close. The difference in τ₀ between the two (0.62 s vs. 0.79 s) is also small in the corresponding Bode plot (i.e., the inset of Fig. 4c), which further confirms the good electrochemical performance of TC_1kg.^49,51 Even at 1–50 A g⁻¹, the C_wt of TC_1kg is quite close to that of TC (i.e., decreasing from 106 to 93 F g⁻¹ at 1 A g⁻¹ and from 71 to 63 F g⁻¹ at 50 A g⁻¹, Fig. 4d). These results for TC_1kg indicate that this method has a small effect on the scaled-up synthesis of TC and the corresponding electrochemical properties.

Fig. 4 Electrochemical performances of symmetric SCs using TC_1kg as electrodes in 1.0 mol L⁻¹ Et₄NBF₄/AN. (a) CV curves at 100 mV s⁻¹; (b) GCD curves at 1 A g⁻¹; (c) Nyquist plots; the inset is the corresponding Bode plot; (d) C_wt at different current densities; (e) Ragone plots; the data for YP50F for typical lead-acid batteries and commercial EDLCs are presented for comparison; (f) cycling stability and coulombic efficiency at 5 A g⁻¹ in 6.0 mol L⁻¹ KOH/H₂O electrolyte. The insets are SEM images for TC_1kg before and after the cycling test. The data for the TC are provided for comparison.

The maximum gravimetric energy density (E_wt) of symmetric SCs with TC as the active material in aqueous electrolyte is 4.4 Wh kg⁻¹, which is comparable to that of commercial EDLCs. However, when Et₄NBF₄/AN was used as the electrolyte, its E_wt reached 27.0 Wh kg⁻¹ (close to that of some conventional lead-acid batteries).³² Even with the kilogram scaled-up of the prepared TC_1kg as the active material, its E_wt could reach 23.6 Wh kg⁻¹ under the same conditions (Fig. 4e), which is only slightly lower than that of TC. Meanwhile, these SCs show good power performance regardless of the use of aqueous or organic electrolytes (Fig. S6, ESI†). This indicates that compared with YP50F, TC containing a large number of mesopores is more favorable for the diffusion of the electrolyte, which can reduce the internal resistance of SCs and improve the power performance.⁵² In addition, TC_1kg exhibits excellent long cycle stability. The capacitance retention and coulombic efficiency are 92.97% and 99.42% (Fig. 4f), respectively, after 50 000 cycles at 5 A g⁻¹, which are significantly better than those of YP50F (Fig. S7, ESI†). This is also supported by the SEM images of the TC_1kg before and after cycling (the insets of Fig. 4f), i.e., there is no obvious change in its morphology after long cycling. In addition, the cost of producing 1 kg of TC, including the consumption of raw materials, energy, and auxiliary materials, is determined to be about 46 RMB (Table S3, ESI†). This indicates that the method proposed in this study for producing TC is indeed cost-effective.

Conclusions

In summary, a low-cost and scalable approach for producing capacitive carbon by ball milling is first proposed, based on the solid–solid inorganic chemical reaction between CaCO₃ and CaC₂. The obtained TC has a high SSA and conductivity; in particular, the SSA exceeds that reported for similar CaC₂-derived carbon. The CaO produced in situ by the solid–solid reaction serves as a template. This strategy not only uses ball milling to form a large number of micropores, but it also works synergistically to promote a large number of mesopores in the TC, opening up new possibilities for the preparation of high-rate capacitive carbon. TC as an electrode outperforms commercial YP50F in terms of C_wt and rate performance. Overall, the feasibility of preparing TC on a kilogram scale, as well as the associated capacitive performance, were extensively proven. The simple, low-cost, and scalable technique, as well as the concept of turning waste into treasure (i.e., changing CO₂ into high-value-added products), offers a novel way to lower the cost of capacitor carbon and promote carbon neutrality.

Author contributions

Yongfeng Bu: conceptualization; methodology; formal analysis; funding acquisition; resources; supervision; writing – review & editing. Shihao Wang: investigation; validation; visualization; writing – original draft. Yuman Li: investigation; validation. Shengda Tang: investigation; validation. Qin Kang: investigation; validation. Zhaomin Zhu: validation. Hui Li: validation. Li Pan: validation. Hongyu Liang: formal analysis; methodology; resources; supervision; data curation; funding acquisition; project administration; writing – review & editing.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

The authors declared that they have no conflicts of interest to this work.

Acknowledgements

This work was financially supported by Key Research and Development Program of Zhenjiang City (CG2023004), National Natural Science Foundation of China (22379055, 21975109, 52075224), and Qinglan Project of Jiangsu Province of China.

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Footnote

† Electronic supplementary information (ESI) available: Additional component characterization of TC; electrochemical performances of symmetric SCs using TC and TC_1kg as electrodes in different electrolytes; cycling stability and coulombic efficiency of YP50F; comparison of TC with carbon derived from different precursors on parameters and capacitance properties; collection for the R_s, R_ct, R_w, and R_ESR of TC and YP50F in different electrolytes. See DOI: https://doi.org/10.1039/d4qi01715c

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