Oxygen evolution-free sodium carbonate composite material as well as preparation method and application thereof

Abstract

The invention discloses an oxygen evolution-free sodium carbonate composite material as well as a preparation method and application thereof. The preparation method of the composite material comprises the following steps: carrying out powder refinement treatment on a sodium carbonate precursor to obtain particles with the average particle size from micron to nanoscale; s2, uniformly mixing the sodium carbonate precursor treated in S1 with a conductive carbon material to form a composite precursor; placing the composite precursor in an inert atmosphere or a reducing atmosphere, calcining the composite precursor at 400-900 DEG C, and then cooling the composite precursor to room temperature to obtain the oxygen evolution-free sodium carbonate composite material, wherein the conductive carbon material is a high-specific-surface-area carbon material of which the surface is rich in at least one of carbonyl, carboxyl and hydroxyl. The composite material obtained by the method disclosed by the invention is applied as a pre-sodium-modified additive, so that the decomposition voltage of the pre-sodium-modified additive can be greatly reduced, and oxygen evolution is effectively inhibited, thereby improving the first-week coulombic efficiency, cycling stability and overall safety performance of the sodium-ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrode material additives, and more particularly to a sodium carbonate composite without oxygen evolution and a preparation method and application thereof. BACKGROUND

[0002] With the continuous rise of energy demand, sodium-ion energy storage systems have become an important candidate technology in large-scale energy storage due to their abundant sodium resources and low cost. However, during the first charging process, a large number of sodium ions are irreversibly consumed by the solid electrolyte interface, resulting in a low first-week coulombic efficiency, which seriously restricts the actual energy density of the battery. Therefore, a sacrificial positive electrode pre-sodium additive based on sodium carbonate (sodium carbonate) is proposed, which has a high theoretical capacity, is easy to obtain raw materials, and is highly compatible with existing electrode manufacturing processes, showing good application potential.

[0003] However, the traditional sodium carbonate additive has two key bottlenecks: first, its electrochemical decomposition starting potential is too high (usually >4.3 V vs. Na + / Na), far exceeding the stable window of conventional electrolytes, which can easily cause electrolyte oxidation and decomposition, resulting in gas production, impedance rise and cycle life decay; second, lattice oxygen is released during the decomposition process, which can easily generate gaseous O2 through O–O coupling, not only causing system expansion, but also possibly causing electrolyte oxidation and other safety hazards. Although researchers have tried to reduce the decomposition energy barrier by introducing catalysts, it is often difficult to balance activity and stability, and it is impossible to fundamentally block the oxygen evolution path.

[0004] Therefore, how to significantly reduce the decomposition potential of sodium carbonate while inhibiting its oxygen evolution side reaction to achieve a high-efficiency, clean and safe pre-sodium process has become a key technical challenge to promote the practicality of sodium-ion energy storage systems. SUMMARY

[0005] Based on the above technical problems existing in the prior art, the present application provides a preparation method of a sodium carbonate composite without oxygen evolution. The method co-calcines sodium carbonate precursor and surface-functionalized conductive carbon material under specific conditions to in-situ construct a nano-composite structure rich in oxygen vacancies and C–O–Na interfacial chemical bonds, which not only retains the high theoretical capacity of sodium carbonate, but also significantly reduces its electrochemical decomposition potential and inhibits oxygen evolution, thereby effectively solving the problems of low utilization and poor safety of existing sacrificial positive electrode additives caused by high decomposition potential and gas evolution side reactions, and further improving the first-week coulombic efficiency, cycle stability and overall safety performance of sodium-ion batteries.

[0006] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0007] A preparation method of a sodium carbonate composite without oxygen evolution, comprising the following steps:

[0008] S1, raw material pretreatment: the sodium carbonate precursor is subjected to powder refinement treatment to obtain particles with an average particle size in the micron to nanometer scale;

[0009] S2, preparation of the precursor: the sodium carbonate precursor treated in S1 is uniformly mixed with a conductive carbon material to form a composite precursor;

[0010] S3, heat treatment: the composite precursor is placed in an inert atmosphere and calcined at 400-900 °C, and then cooled to room temperature to obtain the sodium carbonate composite material without oxygen evolution;

[0011] wherein the conductive carbon material is a high specific surface area carbon material with at least one of a surface rich in carbonyl, carboxyl, and hydroxyl groups.

[0012] In some embodiments, in step S2, the mass ratio of the sodium carbonate precursor to the conductive carbon material is 1-20:1; preferably, 1-10:1; more preferably, 5-8:1. In some embodiments, in step S3, the calcination temperature is 600-900 °C.

[0013] In some embodiments, the sodium carbonate precursor is selected from at least one of sodium carbonate, sodium oxalate, sodium acetate, sodium citrate, sodium propionate, and sodium lactate.

[0014] In some embodiments, in step S1, the sodium carbonate precursor is subjected to refinement treatment using at least one of a self-planetary ball mill, a high-energy sand mill, freeze-drying, spray drying, or air-jet pulverization; after refinement treatment, the particle size of the sodium carbonate precursor is 50 nm-20 μm.

[0015] In some embodiments, the conductive carbon material is obtained by oxidizing and / or acidizing at least one carbon material precursor selected from Ketjen black (KB), Super P, graphene, mesoporous carbon, carbon aerogel, and carbon nanotubes.

[0016] In some embodiments, the oxidizing and / or acidizing treatment is selected from at least one of nitric acid oxidation, hydrogen peroxide oxidation, ozone treatment, and air heat treatment.

[0017] In some embodiments, the oxidizing and / or acidizing treatment is carried out at a temperature of 0-120 °C for 0.5-12 h.

[0018] In some embodiments, in step S3, the inert atmosphere comprises at least one of argon and helium; the reducing atmosphere comprises one of an argon-hydrogen mixed atmosphere and ammonia; in the argon-hydrogen mixed atmosphere, the volume content of H2 is 5%.

[0019] In some implementations, the heating rate in step S3 is 1–20°C / min.

[0020] The present invention also provides a sodium carbonate composite material obtained by the preparation method of any of the above embodiments, wherein the sodium carbonate particles are coated with a continuous carbon layer with a thickness of <10 nm.

[0021] This invention also provides the application of the above-mentioned sodium carbonate composite material as a pre-sodiumization additive.

[0022] The present invention also provides a positive electrode material, the positive electrode material comprising a positive electrode active material and a pre-sodiumized additive, wherein the pre-sodiumized additive is the above-mentioned carbon composite material; the mass of the pre-sodiumized additive is 0.5-10% of the mass of the positive electrode active material.

[0023] In some embodiments, the positive electrode active material is a material capable of reversibly inserting / extracting sodium ions, including but not limited to at least one of layered oxides, polyanionic compounds, Prussian blue analogs, sodium-rich phase oxides, and activated carbon; specifically, including but not limited to Na 0.66 [Li 0.22 Ti 0.78 O2, P2 - Na 0.67 Ni 0.33 Mn 0.67 O2, O3-NaNi 0.5 Mn 0.3 Co 0.2 O2, Na3V2(PO4)3, Na2Fe2(SO4)3, Na2MnFe(CN)6, etc.

[0024] In some embodiments, the positive electrode material comprises, by weight percentage, 30%–90% of positive electrode active material, 1%–50% of the additives, 5%–15% of conductive agent and 1%–15% of binder.

[0025] The present invention also provides a positive electrode, which includes the positive electrode material of any of the above embodiments.

[0026] The present invention also provides an electrochemical energy storage device, which includes the above-mentioned positive electrode, and the electrochemical energy storage device is a sodium-ion battery, a sodium-ion capacitor, etc.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention involves co-calcining a sodium carbonate precursor with a high specific surface area conductive carbon material that has undergone surface oxidation treatment under specific conditions, resulting in an in-situ carbothermic reduction reaction. During this process, the conductive carbon acts as a reducing agent, promoting selective deoxygenation on the surface of the generated sodium carbonate, forming oxygen vacancies with a concentration of not less than 5% in situ. Simultaneously, the functional groups on the surface of the conductive carbon react with Na... + Interfacial condensation or coordination occurs, forming stable C–O–Na type interfacial chemical bonds between sodium carbonate and the carbon matrix, and simultaneously forming a continuous carbon coating layer, thereby constructing a bifunctional active interface with electronic structure regulation capabilities: oxygen vacancy–C–O–Na.

[0029] This bifunctional interface significantly reduces the electrochemical decomposition barrier of sodium carbonate by synergistically regulating the local electron distribution. Specifically, oxygen vacancies, due to their effective positive charge, exert a strong electrostatic attraction on delocalized π electrons in the conductive carbon sp² hybrid network; while the C–O–Na bond acts as a covalent coupling channel, promoting the π electrons to move towards neighboring CO32-. 2- The C–O antibonding orbitals (π*) of the anion undergo partial delocalization. This electron pre-filling effect leads to a decrease in the C–O bond order and a weakening of the bond energy, thereby reducing the CO32- bond strength during the initial charging process. 2- It is easier to release electrons and undergo selective C–O bond breaking, preferentially releasing CO2 rather than generating O2 through a high-energy O–O coupling pathway. The released reactive oxygen atoms are sp... 2 / sp 3 Hybridized carbon sites are instantly captured and converted in situ into C–O or C=O species, completely blocking O–O coupling and O2 precipitation pathways; thus, this invention significantly shifts the decomposition initiation potential of sodium carbonate negatively by more than 300 mV.

[0030] The sodium carbonate composite material obtained by the method of this invention exhibits a significant negative shift in decomposition initiation potential exceeding 300 mV (measured ≤3.9 V), and DEMS confirms O2 release of <5 ppm. The released Na⁺ efficiently compensates for irreversible losses in the first cycle, improving the coulombic efficiency by 8–15%. The interfacial C–O–Na bonds continuously act as an "oxygen buffer" during cycling, inhibiting the O₂-O₃ coupling pathway and interfacial degradation. (0.1 A g) -1 It maintains high specific capacity after 200 cycles at current density and within a voltage window of 2.0–4.0 V, and its coulombic efficiency remains stable at over 99.5%.

[0031] In summary, this invention, through the synergistic use of "interfacial oxygen vacancies + carbon capture" dual sites, is the first to switch the oxidative decomposition of sodium carbonate from the traditional oxygen evolution pathway to a clean, oxygen-free pathway. This significantly reduces the decomposition voltage and the risk of oxygen production, and simultaneously solves the two major bottlenecks of high decomposition potential and oxygen evolution without sacrificing capacity. It provides an ideal pre-sodiumification solution for high-energy-density and high-safety sodium-ion batteries.

[0032] Furthermore, this invention utilizes in-situ carbothermic conversion of conductive carbon and sodium carbonate precursors under a controlled atmosphere, eliminating the need to introduce transition metals or toxic reagents, making it green and environmentally friendly. Attached Figure Description

[0033] Figure 1 Characterization diagrams of the low decomposition potential oxygen-evolution-free sodium carbonate pre-sodiumization additive (denoted as KB@NCO) prepared in Example 1 of this invention, the physical mixture of Ketjen black and sodium carbonate in the comparative example (denoted as KB+NCO), and pure phase sodium carbonate (denoted as NCO) are shown. Among them, figure a is the Fourier transform infrared spectrum (FTIR), figure b is the electron paramagnetic resonance spectrum (EPR), and figures c and d are the X-ray photoelectron spectroscopy (XPS) O 1s plot and Na 1s plot, respectively.

[0034] Figure 2 The figures show a comparison of the electrochemical performance of KB@NCO, KB+NCO and NCO prepared in Example 1; where figure a is a comparison of the decomposition potentials of the three during the first charging process; and figure b is a GITT (gigacurrent galvanostatic titration) spectrum.

[0035] Figure 3 The first-cycle charge-discharge curves of HC / / AC full capacitors with KB@NCO, KB+NCO, and NCO added respectively;

[0036] Figure 4 Rate performance graphs for HC / / AC full capacitors with KB@NCO, KB+NCO, and NCO added respectively;

[0037] Figure 5 Ragone diagrams of HC / / AC sodium ion capacitors with KB@NCO, KB+NCO, and NCO added respectively;

[0038] Figure 6 Comparison of long-cycle performance of HC / / AC full capacitors with KB@NCO, KB+NCO and NCO respectively;

[0039] Figure 7 Comparison of long-cycle performance of HC / / NFPP full cells with KB@NCO, KB+NCO and NCO respectively;

[0040] Figure 8 For KB+N 13 Differential electrochemical mass spectra (DEMS) of CO and KB@NCO; where, figure a is KB+N 13 Figure b shows the DEMS plot of CO, Figure c shows the DEMS plot of KB@NCO, and Figure c shows a comparison of the oxygen evolution of the two.

[0041] Figure 9 For KB+N 13 Comparison of Raman spectra of CO (Figure a) and KB@NCO. Detailed Implementation

[0042] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0044] Example 1

[0045] A method for preparing a low decomposition potential, oxygen-evolution-free sodium carbonate pre-sodiumization additive includes the following steps:

[0046] S1. Raw material pretreatment 1: Sodium oxalate was placed in a high-energy ball mill and ball-milled at 800 rpm for 12 hours under argon protection to obtain nanoparticles with an average particle size of about 100 nm.

[0047] S2, Raw material pretreatment 2: Ketjen black EC-600JD conductive carbon was dispersed in 6 M nitric acid solution, refluxed at 80°C for 6 h, filtered, washed with deionized water until neutral, and vacuum dried at 80°C to obtain oxidized KB with a surface rich in carboxyl / hydroxyl groups.

[0048] S3. Preparation of precursor: The above-treated sodium oxalate and KB oxide were dispersed in water at a mass ratio of 5:1, sonicated for 30 min, and then freeze-dried to obtain a uniform composite precursor; S4. Heat treatment: The composite precursor was placed in a tube furnace and heated to 600°C at 5°C / min under Ar atmosphere, held for 4 h, and then naturally cooled to room temperature to obtain KB@NCO.

[0049] The obtained KB@NCO was characterized, and the results are as follows: Figure 1 As shown. Figure 1In Figure a, no new phase characteristic peaks were observed in KB@NCO, but CO3 was present in KB@NCO. 2- C–O asymmetric stretching vibration peak (~1450 cm⁻¹) -1 The obvious red shift indicates that the C–O bond length has increased and the bond energy has decreased, which is due to electrons filling the antibonding orbitals; Figure 1 The b plot (EPR) shows a strong signal at g = 2.003 for KB@NCO, confirming the presence of a single-electron-occupied oxygen vacancy; Figure 1 In the c-plot (XPS O 1s), KB@NCO shows an electron-rich oxygen peak at 530.0 eV, and the intensity of the C–O–Na bond peak (532.0 eV) is significantly enhanced and slightly negatively shifted, indicating that interfacial electrons are transferred from carbon to oxygen. Figure 1 The d-plot (XPS Na 1s) shows a new peak at 1072.0 eV for KB@NCO, corresponding to Na in the C–O–Na bond. + The physical mixture (KB+NCO) did not show this signal, proving that stable chemical bonds were formed in situ.

[0050] In summary, KB@NCO successfully constructed a bifunctional interface of "oxygen vacancy – C – O – Na", providing a structural basis for low-potential, oxygen evolution-free decomposition.

[0051] Example 2

[0052] A method for preparing a low decomposition potential, oxygen-evolution-free sodium carbonate pre-sodiumization additive includes the following steps:

[0053] S1. Raw material pretreatment 1: Sodium acetate (CH3COONa) is freeze-dried to obtain porous micron particles;

[0054] S2, Raw material pretreatment 2: Graphene oxide (GO) is used as a conductive carbon source without additional treatment;

[0055] S3. Preparation of precursor: Sodium acetate and GO were ultrasonically dispersed in a water / ethanol mixed solvent at a mass ratio of 3:1, and then freeze-dried to obtain the composite precursor.

[0056] S4. Heat treatment: Heat to 700 °C at 10 °C / min in an Ar atmosphere and hold for 2 h. GO is simultaneously reduced to rGO and coated with sodium carbonate.

[0057] Testing revealed that the additive prepared in this embodiment forms a three-dimensional conductive network structure; Raman spectroscopy... D / I G =1.25, indicating high defect density; strong EPR signal, indicating high oxygen vacancy concentration; GITT measurement of Na + The diffusion coefficient is increased by 3 times.

[0058] Example 3

[0059] A method for preparing a low decomposition potential, oxygen-evolution-free sodium carbonate pre-sodiumization additive includes the following steps:

[0060] S1. Raw material pretreatment 1: Sodium citrate (Na3C6H5O7) was spray-dried to obtain micron-sized spherical particles (D50≈ 1.2 μm).

[0061] S2, Raw material pretreatment 2: Super P conductive carbon was stirred in 30% H2O2 solution at 60 °C for 12 h, filtered and dried to obtain surface hydroxylated carbon material;

[0062] S3. Preparation of precursor: Sodium citrate and hydroxylated Super P were mixed in deionized water at a mass ratio of 7:1, magnetically stirred for 2 h, and then vacuum dried at 60°C.

[0063] S4. Heat treatment: Heat to 350°C at 2°C / min in N2 atmosphere, hold for 6 h, and then cool to obtain the additive.

[0064] Testing revealed that the additive prepared in this embodiment has low sodium carbonate crystallinity and a thin carbon coating layer (~5 nm); FTIR showed strong C–O–Na vibration peaks; the first-cycle decomposition potential was 3.92 V, and the O2 precipitation was <10 ppm, making it suitable for heat-sensitive systems.

[0065] Example 4

[0066] S1. Raw material pretreatment 1: Sodium lactate (C3H5NaO3) was vacuum dried and then ball-milled to D50 ≈ 800 nm;

[0067] S2, Raw material pretreatment 2: Carbon nanotubes (CNTs) are treated with ozone for 1 h to introduce oxygen-containing groups on the surface;

[0068] S3. Preparation of precursor: Sodium lactate and ozone-treated CNTs were mixed in isopropanol at a mass ratio of 8:1, dispersed by high-speed shearing for 1 h, and dried at 80 °C.

[0069] S4. Heat treatment: Calcination at 200 °C, 500 °C, and 800 °C for 4 h in an Ar atmosphere (three parallel samples).

[0070] The positive electrode additive obtained in Example 1 was used to prepare a positive electrode sheet, and then its electrochemical performance was tested, as follows:

[0071] 1. Preparation of the positive electrode sheet

[0072] (1) Preparation of sacrificial positive electrode additive (KB@NCO) positive electrode sheet

[0073] Following conventional methods in the art, KB@NCO was used as the active material, mixed with PVDF binder and Super P conductive agent as the positive electrode material. A small amount of N-methylpyrrolidone was added and the mixture was carefully ground in a ball mill jar until the slurry was homogeneous. The resulting uniform slurry was coated onto aluminum foil and vacuum dried at 80°C for 12 h to obtain the KB@NCO positive electrode sheet. The positive electrode material contained 80% positive electrode additive, 10% PVDF, and 10% Super P by mass percentage.

[0074] (2) Preparation of pure-phase sodium carbonate (NCO) positive electrode sheet

[0075] The preparation method of NCO positive electrode is the same as that of KB@NCO positive electrode. The difference is that, by mass percentage, the content of NCO in the positive electrode material is 80%, the content of PVDF is 10%, and the content of Super P is 10%.

[0076] (3) Preparation of positive electrode sheet of carbon material + sodium carbonate mixture (KB+NCO)

[0077] The preparation methods for KB+NCO positive electrode sheets are the same as those for KB@NCO positive electrode sheets. The difference is that, by mass percentage, the content of KB+NCO in the positive electrode material is 80%, the content of PVDF is 10%, and the content of Super P is 10%. Among them, KB is obtained by pretreatment and oxidation of Ketjen black EC-600JD conductive carbon according to the method in Example 1. The mass ratio of KB to NCO in the mixed material is 1:5.

[0078] (4) Preparation of activated carbon (AC) / NCO and AC / KB@NCO positive electrode sheets

[0079] The preparation methods for AC / NCO and AC / KB@NCO positive electrode sheets are the same as those for KB@NCO positive electrode sheets. The difference is that, by mass percentage, the positive electrode material contains 56% AC, 24% NCO (or KB@NCO), 10% PVDF, and 10% Super P.

[0080] (5) Preparation of sodium iron pyrophosphate (NFPP) positive electrode sheet

[0081] The preparation method of NFPP positive electrode is the same as that of KB@NCO positive electrode. The difference is that, by mass percentage, the positive electrode material contains 80% NFPP, 10% PVDF, and 10% Super P.

[0082] (6) Preparation of NFPP / KB@NCO positive electrode sheet

[0083] The preparation method of NFPP / KB@NCO positive electrode is the same as that of NFPP positive electrode. The difference is that, by mass percentage, the NFPP content is 78%, the KB@NCO content is 2%, the PVDF content is 10%, and the Super P content is 10%.

[0084] 2. Preparation of negative electrode sheet

[0085] According to conventional methods in the art, the negative electrode active material, hard carbon material, the binder, sodium methyl cellulose carboxylate, and the conductive agent Super P are mixed as the negative electrode material, and then carefully ground in a ball mill jar with a small amount of distilled water until the slurry is homogeneous. The resulting uniform slurry is coated on copper foil and vacuum dried at 80°C for 12 h to obtain the negative electrode sheet. The negative electrode material contains 80% hard carbon material, 10% sodium methyl cellulose carboxylate, and 10% Super P by mass percentage.

[0086] 3. Electrochemical performance testing

[0087] (1) KB@NCO decomposition potential test

[0088] Following conventional methods in this field, KB@NCO, KB+NCO, and NCO positive electrode sheets were assembled into half-cells with sodium sheets, separators, and electrolytes, respectively. The electrolyte was a 1 mol / L NaPF6 solution dissolved in 100% propylene carbonate, and the separator was a Whatman GF / C glass fiber membrane. Assembly was performed in a glove box using a CR2016 battery case, and charge-discharge tests were conducted. The test results are as follows: Figure 2 As shown.

[0089] like Figure 2 As shown in Figures a and b, the charging plateau of KB@NCO is significantly lower than that of NCO and KB+NCO, and the initial decomposition potential is about 300 mV lower than that of pure NCO, indicating a substantial reduction in its decomposition energy barrier. Simultaneously, the voltage plateau of KB@NCO is flatter, suggesting superior reaction kinetics. In summary, KB@NCO achieves low-potential, high-efficiency, and stable sodium ion release through interface engineering, significantly improving pre-sodiumization performance.

[0090] (2) In order to verify the practical application of KB@NCO in electrochemical energy storage system, sodium-ion capacitors and sodium-ion battery systems were prepared respectively, and their pre-sodiumization effect on anode materials such as hard carbon and battery performance were determined as follows:

[0091] 1. Construct sodium-ion capacitors AC / NCO (KB+NCO or KB@NCO) by cutting the positive electrode sheet of AC / NCO (KB+NCO or KB@NCO) and the negative electrode sheet, diaphragm, and electrolyte respectively.

[0092] 2. Construct a blank sodium ion energy storage system (HC / / NFPP) using cut negative electrode sheets, sodium iron pyrophosphate (NFPP) positive electrode sheets, a diaphragm, and an electrolyte.

[0093] 3. Construct a sodium-ion full cell using the cut negative electrode, NFPP / NCO (KB+NCO or KB@NCO) positive electrode, separator, and electrolyte, and name it HC / / NFPP / NCO (KB+NCO or KB@NCO).

[0094] In the sodium-based energy storage device described above, the negative electrode is the negative electrode prepared above, the electrolyte is an electrolyte of 1 mol / L NaPF6 dissolved in 100% propylene carbonate, and the separator is a Whatman GF / C glass fiber separator.

[0095] The assembled sodium-ion capacitor and sodium-ion battery system were subjected to relevant performance tests, and the test results are as follows: Figures 3-7 As shown.

[0096] like Figure 3 As shown, during the first charging cycle, KB@NCO exhibited a significantly higher discharge specific capacity (approximately 28% higher than NCO), and its dQ / dV curve showed a sharper and stronger decomposition peak at ~3.85 V, indicating that sodium carbonate achieved more complete and efficient oxidative decomposition at a lower potential; while the decomposition peaks of NCO and KB+NCO were weak and broadened, indicating that the reaction was incomplete and side reactions existed.

[0097] like Figure 4 and Figure 5 As shown, the HC / / AC full capacitor with added KB@NCO exhibits superior electrochemical performance at both high rate and high power density: at 10 A g -1 At current density, its specific capacity retention exceeds 80%; simultaneously, at power density of 3 kW kg... -1 At the same time, it still maintains a high energy density (>45 Wh kg). -1 It is significantly better than the control group, demonstrating excellent fast charging and discharging capabilities and power-energy synergy characteristics.

[0098] like Figure 6 As shown, in an HC / / AC sodium ion capacitor at 0.1 A g -1In long-cycle performance tests conducted at current density and a voltage window of 2.0–4.0 V, the device with added KB@NCO maintained high specific capacity after 200 charge-discharge cycles, and the coulombic efficiency remained stable at over 99.5%, indicating that it has excellent cycle reversibility and interface stability.

[0099] like Figure 7 As shown, KB@NCO also exhibits excellent cycle durability in HC / / NFPP sodium-ion full cells.

[0100] like Figure 8 As shown, isotope labeling method is used ( 13 C) In-situ differential electrochemical mass spectrometry (DEMS) analysis was performed on the gas release behavior of KB@NCO and KB+NCO during the charging process. Figure 8 Figure a shows that KB@NCO mainly releases ¹³CO2 during charging, with O2 precipitation below 5 ppm; while Figure 8 In Figure b, KB+NCO is accompanied by a large amount of O2 and a small amount of CO, indicating that its decomposition pathway includes O–O coupling reactions. Figure 8 The c-figure further compares the O2 evolution of the two, and the total oxygen evolution is less than 10% of that of KB+NCO. The O2 signal of KB@NCO is significantly suppressed, which proves that it effectively blocks the oxygen evolution pathway.

[0101] like Figure 9 As shown, the intensity ratio of the D peak to the G peak in the Raman spectrum of KB@NCO (I D / I G The oxygen vacancy-induced electron redistribution in KB@NCO significantly increases the defect density compared to KB+NCO, indicating a higher carbon framework defect density in KB@NCO. This result suggests that in KB@NCO, the oxygen vacancy-induced electron redistribution enhances the active sites of the carbon material, enabling it to efficiently capture and stabilize reactive oxygen species (such as O2) generated during decomposition. - O2 - This prevents the coupling and generation of O2, thus achieving "oxygen-free" decomposition. Therefore, the interfacial C–O–Na bond works synergistically with the highly defective carbon to fundamentally suppress side reactions by directly adsorbing and converting reactive oxygen species.

[0102] In summary, KB@NCO, by constructing an "oxygen vacancy–C–O–Na" interface structure, not only weakens the C–O bond to reduce the decomposition potential, but also utilizes carbon defect sites to achieve in-situ capture of reactive oxygen species, thus realizing a clean and safe pre-sodiumification process.

[0103] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0104] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing an oxygen-evolving sodium carbonate composite material, characterized in that, Includes the following steps: S1. Raw material pretreatment: The sodium carbonate precursor is subjected to powder refinement treatment to obtain particles with an average particle size in the micrometer to nanometer scale. S2. Preparation of precursor: The sodium carbonate precursor treated with S1 is uniformly mixed with conductive carbon material to form a composite precursor; S3. Heat treatment: The composite precursor is placed in an inert or reducing atmosphere and calcined at 400–900 °C, and then cooled to room temperature to obtain the oxygen-free sodium carbonate composite material. The conductive carbon material is a high specific surface area carbon material whose surface is rich in at least one of carbonyl, carboxyl, and hydroxyl groups.

2. The method for preparing the oxygen-free sodium carbonate composite material according to claim 1, characterized in that, In step S2, the mass ratio of the sodium carbonate precursor to the conductive carbon material is 1-20:

1.

3. The method for preparing the oxygen-free sodium carbonate composite material according to claim 1, characterized in that, The sodium carbonate precursor is selected from at least one of sodium carbonate, sodium oxalate, sodium acetate, sodium citrate, sodium propionate, and sodium lactate.

4. The method for preparing the oxygen-free sodium carbonate composite material according to claim 1, characterized in that, In step S1, the sodium carbonate precursor is refined using at least one of the following methods: planetary ball milling, high-energy sand milling, freeze drying, spray drying, or air jet milling; after refinement, the particle size of the sodium carbonate precursor is 50 nm-20 μm.

5. The method for preparing the oxygen-free sodium carbonate composite material according to claim 1, characterized in that, The conductive carbon material is obtained by oxidation and / or acidification of at least one carbon material precursor selected from Ketjen Black, Super P, graphene, mesoporous carbon, carbon aerogel, or carbon nanotubes.

6. The sodium carbonate composite material obtained by the preparation method according to any one of claims 1-5.

7. The use of the sodium carbonate composite material according to claim 6 as a pre-sodiumization additive.

8. A positive electrode material, characterized in that, Including the sodium carbonate composite material as described in claim 7.

9. A positive electrode, characterized in that, Includes the cathode material as described in claim 8.

10. An electrochemical energy storage device, characterized in that, Includes the positive electrode as described in claim 9.

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