All-carbon sodium ion hybrid capacitance system based on heterogeneous carbon electrode

Abstract

The invention discloses an all-carbon sodium ion hybrid capacitor system based on a heterogeneous carbon electrode, the all-carbon sodium ion hybrid capacitor system comprises an energy type capacitor system and a rate type capacitor system, for the energy type capacitor system, an ultrahigh specific surface area (SBETgt; the micropore-rich positive electrode (3,600 m < 2 > / g) is matched with the hard carbon negative electrode, and the device shows excellent comprehensive performance under the wide voltage window of 0-4V and the mass ratio of the positive electrode active material to the negative electrode active material of 1: 2; for a power type capacitor system, a positive electrode rich in mesopores and having a graphitized microcrystalline structure is selected to be matched with a modified negative electrode of an expanded layer, so that charge transfer resistance and ion diffusion resistance are effectively reduced, and the problem that a traditional hard carbon negative electrode is seriously polarized under rapid charging and discharging is solved; the device can still keep stable energy supply under extremely high power output, and balance between high power and practical capacity is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical energy storage, and relates to a hybrid supercapacitor, in particular to a full-carbon sodium-ion capacitor system which realizes performance customization through directional regulation of positive and negative electrode microstructure parameters according to application scene requirements (high energy density or high power density). BACKGROUND

[0002] With large-scale renewable energy grid-connection and the increasing demand for grid stability, it is an urgent need to develop a new energy storage system with high energy density, high power density, long cycle life and low cost. Although lithium-ion batteries (LIBs) have high energy density, they have low power density, limited cycle life and potential safety hazards. While traditional double-layer supercapacitors (SCs) have extremely high power density and cycle life, they have extremely low energy density (< 20 Wh kg -1 ), which cannot meet the demand of large-scale energy storage. Sodium-ion capacitors (SICs) as a new type of energy storage device combine the battery-type negative electrode of sodium-ion batteries (SIBs) and the capacitor-type positive electrode of supercapacitors. They have attracted widespread attention due to their advantages of high energy density, high power density, abundant sodium resources and low cost. However, the development of existing SICs technology faces a core bottleneck: the mismatch between the kinetics and capacity of the positive and negative electrodes.

[0003] In the selection of negative electrode materials for SICs, due to the fact that the radius of sodium ion (Na + ) is much larger than that of lithium ion (Li + ) (0.076 nm), Na + cannot be effectively embedded in commercial graphite negative electrodes (with extremely low capacity, about 35 mAh g -1 ). Therefore, research has shifted to non-graphitic carbon materials, especially microcrystalline carbon (such as hard carbon). Hard carbon has an expanded interlayer spacing of microcrystalline layers (> 0.36 nm), showing high sodium storage capacity, and is considered one of the most promising SICs negative electrode materials.

[0004] However, the hard carbon negative electrode for SICs in the prior art has a serious rate performance (kinetics) defect. The sodium storage mechanism of hard carbon includes surface adsorption in the high-voltage slope region (fast kinetics) and interlayer insertion / closed pore filling in the low-voltage platform region (slow kinetics). The high energy density of SICs mainly comes from the low-voltage platform region of the hard carbon negative electrode, but the Na + diffusion rate in this region is extremely slow, which leads to a serious kinetic mismatch between the positive and negative electrodes of SICs, limiting the power density of the device. To solve the kinetic problem of the hard carbon negative electrode, existing technologies mainly focus on regulating the carbon structure, especially expanding the interlayer spacing of the microcrystalline layers (d 002 ) to accelerate Na+ However, the existing interlayer spacing regulation methods have significant defects: (1) Template method or severe heat treatment: For example, Qiu D. et al. (Journal of Energy Chemistry, 2019, 31: 101-106) prepared porous hard carbon using NaCl template, and Mahmood A. et al. (Energy Storage Materials, 2021, 41:395-403) prepared graphene paper using explosive heating. Although these methods improved the rate performance, the large number of pores introduced led to excessive consumption of electrolyte, and the initial coulombic efficiency (ICE) was extremely low (for example, Qiu et al. reported only 60%). (2) Molecular / atomic intercalation method: For example, Zhang Y.S. et al. (Energy Storage Materials, 2021, 34: 45-52) intercalated diamine molecules into graphene oxide; Hong Z. et al. (Advanced Materials, 2018, 30(29): 1802035) used molten salt method to dope sulfur (S); Wu F. et al. (ACS Applied Materials & Interfaces, 2018, 10(32):27030-27038) used biomass self-doping potassium (K). Although these methods successfully expanded the interlayer spacing, they were accompanied by extremely low initial coulombic efficiency (ICE of only 38.4%, 56% and 69.2%, respectively), which was unacceptable in practical applications. Therefore, there is an urgent need in the prior art for a method that can effectively expand the interlayer spacing of the crystallite without sacrificing the initial coulombic efficiency (ICE) and reversible capacity, significantly improve the Na + diffusion dynamics.

[0005] In terms of positive electrode materials of SICs, the specific capacity is usually much lower than that of the negative electrode, which is another key bottleneck limiting the energy density of SICs. Porous carbon is the most commonly used positive electrode material for SICs. Existing research shows that porous carbon with high specific capacitance needs to meet two structural requirements: (1) extremely high specific surface area and abundant micropores. The pioneering research of Chmiola J. et al. (Science, 2006, 313(5794): 1760-1763) pointed out that when the pore size is less than 1 nm, the capacitance will increase abnormally, indicating that abundant micropores are the basis for achieving high capacity storage. (2) Hierarchical pore structure (micropore / mesopore): a pure micropore structure will lead to difficult ion transport. For example, the research of Wu M. et al. (Chemical Engineering Journal, 2014, 245: 166-172) pointed out that the introduction of a certain amount of mesopores (mesopores) to form a hierarchical pore channel is beneficial to the penetration of electrolyte and the rapid diffusion of ions, which is necessary to achieve high rate performance.

[0006] The raw materials and methods for preparing such porous carbon are various. Taking coal as the raw material, especially using KOH activation method, is considered to be an effective way to prepare low-cost and high-performance porous carbon. For example, Shi M. et al. (Journal of Alloys and Compounds, 2021, 859: 157856) used KOH activation of anthracite to obtain a specific surface area of up to 3550.7 m 2 g -1 . In addition, Sun F. et al. (Journal of Power Sources, 2020, 477: 228759) found that high-temperature KOH activation can also promote the graphitization of the carbon skeleton, which helps to improve the conductivity and structural stability of the positive electrode material. However, how to optimize the activation process to prepare a positive electrode material with ultra-high specific surface area, reasonable micropore / mesopore ratio and good conductivity from low-cost lignite as raw material according to the needs of SICs is still a challenge for existing technology.

[0007] In summary, the existing SICs technology has the following key problems: (1) the slow kinetics in the low-voltage platform region of the negative electrode hard carbon leads to a mismatch with the positive electrode dynamics; (2) the existing negative electrode modification methods (such as expanding the interlayer spacing) severely sacrifice the initial coulombic efficiency (ICE); (3) the specific capacity and rate performance of the positive electrode porous carbon still need to be optimized to match the negative electrode. Therefore, developing new paths for preparing high-performance positive and negative electrode materials, improving the rate performance of the negative electrode (especially the kinetics in the platform region) by regulating the microcrystalline structure and closed pore structure of the carbon material, and improving the capacity performance of the positive electrode by regulating the pore structure and functional group content of the carbon material, realizing the directional design and matching based on heterogeneous carbon materials, are urgent problems to be solved. SUMMARY

[0008] This invention provides a hybrid capacitor system of all-carbon sodium ions based on heterogeneous carbon electrodes, aiming to solve how to construct differentiated capacitor systems by quantifying key structural parameters of the positive and negative electrodes (such as the proportion of micropores and the spacing between microcrystal layers), thereby breaking through the energy density bottleneck and the power density bottleneck respectively.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A hybrid capacitor system based on heterogeneous carbon electrodes and sodium ions of all carbon comprises an energy-type (high energy density) capacitor system and a rate-type (high power density) capacitor system, wherein:

[0011] The positive electrode of the energy-type (high energy density) capacitor system is selected from activated carbon with ultra-high specific surface area and abundant microporous structure. Specific structural parameters must meet the following requirements: specific surface area S BET > 3600 m 2 g -1 And the micropore volume V micro ≥1.90cm 3 g -1 The negative electrode is made of microcrystalline carbon material with high voltage plateau capacity; the mass ratio of positive to negative electrode active materials is 0.5~3:1, preferably 2:1, and it operates in a voltage window of 0~4V.

[0012] The positive electrode of the rate-multiplier (high power density) capacitor system is made of carbon material with a hierarchical pore structure and a high degree of graphitization. Specific structural parameters must meet the following requirements: micropore volume ratio V micro / V total < 40%, and a distinct (002) graphitization peak appears at 26.2° in the XRD pattern; the negative electrode is made of microcrystalline carbon modified by methods such as molten salt post-treatment, and the key parameter must meet the microcrystalline interlayer spacing d. 002 >0.38 nm, the preferred mass ratio of positive to negative electrode active materials is 0.5~3:1, preferably 2:1.

[0013] In this invention, the microcrystalline carbon is preferably a carbon material obtained by molten salt modification, and the specific modification steps are as follows:

[0014] Step 1, Carbonization: Select raw coal such as lignite, bituminous coal, and anthracite as raw materials, and prepare hard carbon precursors through high-temperature carbonization. Control the heating rate to be 2~10℃ / min, the high-temperature carbonization temperature to be 1000~1600℃, and the time to be 1~12h.

[0015] Step 2, Molten Salt Mixing: Thoroughly mix the hard carbon precursor with the LiCl / KCl binary molten salt, controlling the mass ratio of the hard carbon precursor to the LiCl / KCl binary molten salt to be 1:5~50, the mass ratio of LiCl to KCl to be 4.5:5.5, and the preferred mass ratio of hard carbon, LiCl, and KCl to be 1:4.5:5.5;

[0016] Step 3: Low-temperature molten salt heat treatment: The molten salt mixture is heat-treated to bring the binary salt into a molten liquid phase activated state. The heating rate is controlled at 2~10℃ / min, the heat treatment temperature is 400~700℃, preferably 550℃, and the heat treatment time is 1~12 hours.

[0017] Step 4, molten salt removal: After heat treatment, wash repeatedly with hot water until no chloride ions can be detected, then vacuum dry to obtain modified hard carbon.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) A system-level matching strategy for differentiated application needs was proposed, realizing the targeted customization of device performance. This invention breaks the limitation of the independent development of positive and negative electrode materials in traditional sodium-ion capacitor research, and innovatively establishes a matching criterion based on the microstructure of carbon materials (pore size distribution, interlayer spacing, and graphitization degree). For high energy density requirements, this invention maximizes the utilization rate of energy storage sites by matching positive electrodes with high micropores / high adsorption sites with negative electrodes with high plateau capacity; for high power density requirements, this invention establishes a low-impedance high-speed ion transport channel by matching positive electrodes with hierarchical pores / high conductivity with negative electrodes with rapid diffusion. This on-demand matching design method enables this invention to flexibly adapt to various application scenarios from long-term energy storage to high-frequency pulse output.

[0020] (2) Two types of high-performance heterogeneous carbon capacitor systems were constructed, overcoming the energy and power bottlenecks respectively. For the energy-type system, by selecting ultra-high specific surface area (S BET >3600 m 2 A microporous positive electrode (such as AC700) with a density of 1 / g is matched with a hard carbon negative electrode. Under a wide voltage window of 0~4V and a positive to negative electrode active material mass ratio of 1:2, the device exhibits excellent overall performance: at 135.2 W kg / g. -1 At a power density of [value missing], the energy density reaches as high as 157.2 Wh / kg. -1 ; at 4883.3 W kg -1 Even at high power densities, the energy density remains at 69.2 Wh / kg. -1It is significantly superior to existing commercial supercapacitors and most sodium-ion capacitors reported in the literature. For power systems, by selecting a positive electrode with rich mesopores and graphitized microcrystalline structure (such as AC900) and matching it with a layer-expanded modified negative electrode, the charge transfer resistance (Rct) and ion diffusion resistance are effectively reduced. This solves the problem of severe polarization of traditional hard carbon negative electrodes under rapid charge and discharge, enabling the device to maintain a stable energy supply under extremely high power output, and achieving a balance between high power and practical capacity.

[0021] (3) This invention overcomes the technical challenge of achieving both anode layer expansion modification and high initial efficiency, significantly improving the system's practicality. Existing technologies typically employ drastic pore-forming or intercalation methods to improve anode kinetics, leading to a sharp drop in initial coulombic efficiency (ICE) (usually <70%), which fails to meet the actual assembly requirements of full cells. The mild molten salt post-treatment strategy adopted in this invention successfully expands the interlayer spacing (e.g., from 0.378 nm to 0.381 nm) to accelerate Na + While transmitting power, the excessive increase (and even slight decrease) in specific surface area was suppressed, thus maintaining an extremely high initial coulombic efficiency (>80%) for the anode material. This technological breakthrough is the material basis for constructing high-power and long-life practical devices.

[0022] (4) This invention discovers that the final performance (energy type or rate type) of a capacitor depends on the synergistic matching of key structural parameters of the positive and negative electrode materials. The design method provided by this invention achieves directional matching of the positive and negative electrode structures and dynamics by controlling the carbonization path to obtain different results, providing an effective technical path for developing low-cost, high-energy, and high-power all-carbon sodium-ion capacitors. Attached Figure Description

[0023] Figure 1 XRD patterns of HC1300 and HC1300-KCl / LiCl-550-4h;

[0024] Figure 2 The pore structures of HC1300 and HC1300-KCl / LiCl-550-4h are shown in (a) N2 adsorption isotherms of HC1300 and HC1300-KCl / LiCl-550-4h, and (b) pore size distribution curves.

[0025] Figure 3 The effects of pore structure regulation on HC1300 and HC1300-KCl / LiCl-550-4h: (a) rate performance, (b) cycle performance;

[0026] Figure 4 The pore evolution of porous carbon obtained from Bori-Xile lignite activated by KOH at different temperatures is shown in (a) N2 adsorption isotherm and (b) pore size distribution curve.

[0027] Figure 5 XRD results of porous carbon obtained from KOH-activated Borgishile lignite at different temperatures;

[0028] Figure 6 For the electrochemical fingerprint characteristics of AC samples in a half-cell, (a) at 1 mV s -1 (a) CV curve at sweep rate; (b) at 50 mV s -1 CV curves at scan rate; (c) at 0.2A g -1 GC curves at current density; (d) at 10 A g -1 GC curves at current density;

[0029] Figure 7 The electrochemical performance of cathode materials with different pore structures in half-cells is shown in the figures: (a) GC curves of AC700 at various current densities; (b) rate performance of AC samples; and (c) cycle performance.

[0030] Figure 8 The process for optimizing the operating voltage window of a full-carbon sodium-ion capacitor, (ab)SiC at 1 mV s -1 Voltage sweep rate and CV curves under different voltage windows; (c) SiC at 1 mV s -1 (d) Voltage sweep rate and CV curves under the 0-4V voltage window; GCD curve of SiC under the 0-4V voltage window;

[0031] Figure 9 HC1300-KCl / LiCl-550-4h / / AC700 1 mV s -1 CV curve at voltage sweep rate;

[0032] Figure 10 0.05A g -1 GCD curves at current density;

[0033] Figure 11 Electrochemical performance of HC1300-KCl / LiCl-550-4h / / AC700: (ac) GCD curves at various current densities, (d) Ragone plot.

[0034] Figure 12 The cycling performance of HC1300-KCl / LiCl-550-4h / / AC700 1:2 was measured. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0036] This invention provides a method for constructing an all-carbon sodium-ion hybrid capacitor system based on heterogeneous carbon electrodes. The main technical problem to be solved by this method is to overcome the fundamental kinetic and capacitance mismatch between the positive and negative electrodes in existing all-carbon sodium-ion capacitors (SICs). This main technical problem is specifically broken down into the following three aspects: (1) the negative electrode kinetic problem, solving the problem of microcrystalline carbon material as the negative electrode, especially in the low voltage plateau region (0~0.1 Vvs Na / Na) that determines the energy density of the device. + (1) The problem of poor rate performance due to slow diffusion of sodium ions. (2) The problem of practicality of the negative electrode. When improving the kinetics of the negative electrode (e.g., by increasing the interlayer spacing), the existing technology generally introduces a large number of pores or defects, which leads to a serious reduction in the initial coulombic efficiency (ICE) and thus becomes a bottleneck for practical application. (3) The problem of capacity of the positive electrode. The problem of low specific capacitance of porous carbon materials as positive electrodes. That is, how to prepare carbon materials with ultra-high specific surface area, rich micropores and reasonable hierarchical pore structure, and suitable functional group types and distribution to improve their sodium storage capacity, so as to achieve capacity and kinetic matching with the negative electrode. The secondary technical problem to be solved is: to provide a low-cost method for preparing heterogeneous carbon materials. That is, by directional control of the multi-scale structure of the material, high-performance microcrystalline carbon negative electrodes and high-capacity porous carbon positive electrodes with the above-mentioned performance matching and structural characteristics are obtained respectively, so as to achieve low-cost manufacturing of devices. The specific implementation steps are as follows:

[0037] (1) System design of energy-type (high energy density) capacitors: This system aims to maximize the charge storage sites per unit mass. The positive electrode is selected from activated carbon with ultra-high specific surface area and abundant microporous structure. Specific structural parameters must meet the following requirements: specific surface area S BET > 3600 m 2 g -1 And the micropore volume V micro > 1.90 cm 3 g -1 Abundant micropores provide numerous physical adsorption sites for anions. The negative electrode is made of microcrystalline carbon material with a high voltage plateau capacity (such as hard carbon that has not been over-layered or is highly crystalline), utilizing its interlayer intercalation and closed-pore filling mechanisms to provide high capacity. The mass ratio of the positive to negative electrode active materials is 0.5~3:1, preferably 2:1, operating within a 0~4V voltage window. This wide voltage range balances the capacities of the two electrodes, maximizing the device's energy density.

[0038] (2) System design of rate-capacitor (high power density): This system aims to minimize ion transport resistance and charge transfer resistance, and adapt to rapid charge and discharge. The positive electrode is made of carbon material with a hierarchical pore structure and a high degree of graphitization. Specific structural parameters must meet the following requirements: micropore volume ratio V micro / V total <40% (i.e., well-developed mesopores / macropores, facilitating electrolyte wetting and rapid ion transport), and a distinct (002) graphitization peak at 26.2° in the XRD pattern (improving conductivity). The negative electrode is made of microcrystalline carbon modified by methods such as molten salt post-treatment, and the key parameter must meet the microcrystalline interlayer spacing d. 002 >0.38 nm. The mass ratio of positive to negative electrode active materials is 0.5~3:1, preferably 2:1. The increased interlayer spacing significantly reduces the diffusion barrier of sodium ions, matching the fast kinetics of the positive electrode. By employing a thinner electrode coating and an optimized positive to negative electrode ratio to construct the system, the charge transfer resistance (Rc) is reduced. ct This enables high power output.

[0039] Example 1: Construction of a high-energy SiC system

[0040] The positive electrode uses AC700 (high micropore, S) BET =3638 m 2 / g, V micro =1.90 cm3 / g). The negative electrode used was HC1300 (or conventional hard carbon). The electrolyte was 1M NaClO4 (EC:DEC=1:1 Vol%), and the glass fiber separator was Whatman GF / D. The experiment used CR2032 coin cells to assemble coin cells, and the assembly process was carried out in an argon-filled glove box.

[0041] In this embodiment, both the negative electrode and the positive electrode are prepared from the same lignite. Specifically, the positive electrode is prepared by KOH activation method with an alkali-to-carbon mass ratio of 2, activated at 700°C for 2 hours under nitrogen atmosphere; the negative electrode is obtained by direct carbonization of lignite at 1300°C with a heating rate of 5°C / min, held for 2 hours under argon atmosphere.

[0042] Example 2: Construction of a high-power SiC system

[0043] The positive electrode uses AC900 (rich in mesopores, V). micro / V total =37.63%, with graphitization peaks). The negative electrode uses HC1300-KCl / LiCl-550-4h (extensively layered hard carbon, d...). 002=0.381 nm). The electrolyte was 1M NaClO4 (EC:DEC=1:1 Vol%), and the glass fiber separator was Whatman GF / D. The experiment used CR2032 coin cells to assemble coin cells, and the assembly process was carried out in an argon-filled glove box.

[0044] In this embodiment, the positive electrode is prepared from lignite using KOH activation method, with an alkali-to-carbon mass ratio of 2, and activation temperature of 900℃ for 2 hours under nitrogen atmosphere.

[0045] In this embodiment, the negative electrode is prepared according to the following steps:

[0046] (1) Raw material pretreatment: The Baorixile lignite was crushed and sieved (>200 mesh), and then washed with 5 M HCl and 10 wt% acid to remove impurities. After washing with water until neutral, it was dried.

[0047] (2) Carbonization: The pretreated coal powder was heated to 1300℃ at 5℃ / min under an argon atmosphere and kept at the temperature for 2 hours to obtain the precursor hard carbon HC1300.

[0048] (3) Molten salt modification: Weigh 0.1g HC1300, 0.45g LiCl and 0.55g KCl, grind and mix them evenly.

[0049] (4) Heat treatment: The mixture is placed in a corundum boat and heated to 550°C at 5°C / min under a nitrogen flow (50 sccm) and held for 4 hours.

[0050] (5) Post-treatment: After cooling, the filtrate is repeatedly filtered and washed with hot water until it is neutral and free of chloride ions. It is then vacuum dried at 80°C for 12 hours to obtain modified hard carbon HC1300-KCl / LiCl-550-4h.

[0051] 1. Negative electrode side: Proving that the modified negative electrode possesses the foundation for high power and high first-efficiency.

[0052] Figure 1 The changes in the crystal structure of the hard carbon anode before and after modification are shown in the figure. As can be seen from the figure, compared to the original HC1300, the modified HC1300-KCl / LiCl-550-4h exhibits a significant leftward shift in the (002) diffraction peak near 23°. Based on the Bragg equation (as shown in Table 1), its interlayer spacing (d) is calculated to be... 002 The interlayer spacing was extended from 0.378 nm to 0.381 nm. This increased interlayer spacing lowers the energy barrier for sodium ion insertion between graphite microcrystals, providing a high-speed channel for rapid sodium ion transport, which is a key prerequisite for building high-power systems.

[0053] Figure 2The pore structure of the negative electrode before and after modification was compared. It is noteworthy that after molten salt treatment, the N2 adsorption-desorption isotherm of HC1300-KCl / LiCl-550-4h was... Figure 2 a) No significant adsorption growth was observed in the low-pressure region; in fact, the specific surface area even decreased slightly. This indicates that molten salt treatment is highly selective: while effectively expanding the internal microcrystalline interlayer spacing, it did not etch a large number of openings on the carbon surface that would lead to side reactions. Figure 2 The pore size distribution of b, this unique microstructure ensures that the material can maintain a high initial coulombic efficiency (ICE) while having fast ion channels.

[0054] Figure 3 This directly verified the effectiveness of the aforementioned structural adjustments. In the rate performance test ( Figure 3 a) Even at a high current of 2.0C, the capacity retention of the modified negative electrode is significantly better than that of the unmodified sample. More importantly, Figure 3 b shows that the modified anode achieved an initial coulombic efficiency (ICE) of 80.2%. This coexistence of high rate capability and high initial efficiency demonstrates that the anode material can perfectly match the requirements of high-power capacitor systems for fast response and high energy efficiency.

[0055] 2. Positive side: This demonstrates that the AC900 possesses high-power structural characteristics.

[0056] Figure 4 The pore evolution of porous carbon cathodes at different activation temperatures is demonstrated, revealing the material basis for the differentiated matching of the system in this invention. For example... Figure 4 As shown in Figure a, AC700 exhibits the most pronounced type I isotherm characteristics, with a sharp increase in adsorption capacity in the low relative pressure region, indicating its extremely rich microporous structure. Table 2 data confirms that the micropore volume of AC700 is as high as 1.90 cm³. 3 g -1 This micropore-dominated structure provides the largest number of ion adsorption sites, establishing its position as the preferred cathode for high-energy systems. In contrast, the AC900 isotherm exhibits a distinct H4-type hysteresis loop, and... Figure 4 The pore size distribution of b shows a significant increase in mesopores within the 2–50 nm range. Table 2 data shows that the micropore ratio of AC900 is only 37.63%. This well-developed mesopore / macropore network constitutes a "highway" for electrolyte ions, greatly reducing the transport resistance of ions inside the electrode, making it an ideal cathode match for high-power systems.

[0057] Figure 5Further analysis revealed the differences in the crystal structure of the cathode materials. As the activation temperature increased to 900℃ (AC900), a distinct sharp diffraction peak appeared at 26.2° in the XRD pattern. This corresponds to the (002) crystal plane of the graphite structure, indicating that AC900 possesses a high degree of graphitization. This high degree of graphitization endows the material with excellent intrinsic electronic conductivity, significantly reducing ohmic polarization under high-current charge and discharge. This, combined with the aforementioned mesoporous structure, ensures the realization of a power-type system from both electronic conduction and ion transport perspectives.

[0058] 3. Electrochemical performance verification

[0059] Figure 6 This demonstrates the electrochemical fingerprint characteristics of cathode materials with different pore structures in half-cells. For example... Figure 6 As shown in Figure a, AC700 exhibits the largest enclosing area, corresponding to its highest micropore volume, proving that it is best suited for energy-type systems; while samples such as AC900 exhibit different rectangular characteristics, indicating that changes in pore structure directly regulate charge storage behavior, providing a basis for cathode selection based on different needs.

[0060] Figure 7 b summarizes the rate performance of various cathode materials. This result establishes a cathode performance database, enabling the present invention to select the most suitable active material based on a preset energy or power target.

[0061] Figure 8 The optimization process of the operating voltage window of an all-carbon sodium-ion capacitor is demonstrated. Tests show that when the voltage window is widened to 0~4V ( Figure 8 c) No obvious polarization or side reaction peaks were observed in the device, and the discharge curve remained linear. Figure 8 d). This demonstrates that the positive and negative electrode materials selected in this invention have good electrochemical stability over this wide voltage range, which is a prerequisite for achieving high energy density.

[0062] To address the core issue of capacity and kinetic mismatch between the positive and negative electrodes, this invention systematically regulates the mass ratio of the active materials in the positive and negative electrodes. For example... Figure 9 and Figure 10 As shown, when the mass ratio of the positive and negative electrodes is adjusted to 1:2, the CV curve exhibits the most standard rectangular characteristic, and the GCD curve shows the longest charge-discharge time. This indicates that at this point, the anion adsorption capacity of the positive electrode and the cation intercalation capacity of the negative electrode reach the optimal thermodynamic and kinetic balance.

[0063] Figure 11Figure d visually illustrates the relationship between energy density and power density of the optimized system (1:2 mass ratio) constructed in this invention. Thanks to the synergistic matching of the highly microporous positive electrode and the expanded-layer negative electrode, this device achieves an energy density as high as 157.2 Wh / kg at an output power of 135.2 W / kg, successfully breaking through the energy bottleneck of traditional capacitors. Simultaneously, the extension of the curve in the high-power region indicates that the system still maintains a good kinetic response. For further improvement in performance at extremely high rates, the screening strategy of this invention can be used to select... Figure 6 The AC900 positive electrode has better conductivity.

[0064] Figure 12 The practical potential of the system was confirmed. After 1500 cycles at a current density of 0.5 A / g, the capacity retention rate was still as high as 86.3%, proving that the molten salt modified extended layer anode did not sacrifice the structural stability of the material and achieved a long cycle life.

[0065] Tables 1 and 2 correspond to the microcrystalline parameters of the positive and negative electrode carbon materials, respectively. The key to selecting the positive and negative electrode materials when designing high-power / high-energy capacitors lies in the carbon microcrystalline parameters, which can be used to match the appropriate positive and negative electrodes as needed.

[0066]

[0067]

Claims

1. A hybrid capacitor system of all-carbon sodium ions based on heterogeneous carbon electrodes, characterized in that... The all-carbon sodium ion mixed capacitor system is a high energy density capacitor system, and the positive electrode is selected from activated carbon with ultra-high specific surface area and rich microporous structure. The negative electrode is made of microcrystalline carbon material with high voltage plateau capacity; it operates within a voltage window of 0~4V.

2. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 1, characterized in that... The specific surface area S of the positive electrode BET > 3600 m 2 g -1 And the micropore volume V micro ≥1.90 cm 3 g -1 .

3. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 1, characterized in that... The mass ratio of the active materials in the positive electrode to the negative electrode is 0.5 to 3:

1.

4. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 3, characterized in that... The mass ratio of the active materials in the positive and negative electrodes is 2:

1.

5. A hybrid capacitor system of all-carbon sodium ions based on heterogeneous carbon electrodes, characterized in that... The all-carbon sodium ion hybrid capacitor system is a high power density capacitor system. The positive electrode is made of carbon material with hierarchical pore structure and high graphitization degree, and the negative electrode is made of microcrystalline carbon.

6. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 5, characterized in that... The micropore volume ratio V of the positive electrode micro / V total < 40%, and a distinct (002) graphitization peak appears at 26.2° in the XRD pattern.

7. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 5, characterized in that... The interlayer spacing d of the negative electrode 002 >0.38 nm.

8. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 5, characterized in that... The mass ratio of the active materials in the positive electrode to the negative electrode is 0.5 to 3:

1.

9. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 8, characterized in that... The mass ratio of the active materials in the positive and negative electrodes is 2:

1.

10. The all-carbon sodium ion hybrid capacitor system based on heterogeneous carbon electrodes according to claim 1, as described in claim 5, is characterized in that... The microcrystalline carbon is a carbon material obtained by molten salt modification. The specific modification steps are as follows: Step 1, Carbonization: Select lignite, bituminous coal or anthracite as raw materials, and prepare hard carbon precursors by high-temperature carbonization. Control the heating rate to be 2~10℃ / min, the high-temperature carbonization temperature to be 1000~1600℃, and the time to be 1~12h. Step 2, Molten Salt Mixing: Thoroughly mix the hard carbon precursor with the LiCl / KCl binary molten salt, controlling the mass ratio of the hard carbon precursor to the LiCl / KCl binary molten salt to be 1:5~50, and the mass ratio of LiCl to KCl to be 4.5:5.5; Step 3, Low-temperature molten salt heat treatment: Heat treat the molten salt mixture to bring the binary salt to a molten liquid phase activated state. Control the heating rate to be 2~10℃ / min, the heat treatment temperature to be 400~700℃, and the heat treatment time to be 1~12 hours. Step 4, molten salt removal: After heat treatment, wash repeatedly with hot water until no chloride ions can be detected, then vacuum dry to obtain modified hard carbon.

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