A composite sodium supplement, its preparation method and application

Abstract

The application discloses a kind of composite sodium supplement agent and its preparation method and application, belong to the technical field of sodium ion battery, solve the problem of low battery stability in prior art with the process of sodium carbonate as sodium supplement agent Complicated,It is composed of sodium ion battery layered oxide and sodium carbonate with mass ratio of 1:0.1~10.The sodium carbonate and layered oxide in the composite sodium supplement agent provided by the application can release active sodium ions, and the introduction of non-active substance carbon is avoided, the volume specific capacity of the sodium supplement agent is improved, an efficient composite pre-sodium system is constructed, and excellent sodium supplement performance can be achieved.The irreversible capacity loss of active sodium ions can be effectively supplemented in the full battery, and the energy density of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically to a composite sodium supplement agent, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries are one of the most promising technologies in the field of large-scale energy storage. With the deepening research on sodium-ion battery technology in recent years, the electrochemical performance of sodium-ion batteries has been greatly improved. However, in practical sodium-ion battery cells, the initial coulombic efficiency of the negative electrode is generally low, leading to irreversible insertion / extraction of some sodium ions on the negative electrode side. This consumes active sodium ions during cycling, resulting in overall capacity decay and a decrease in energy density. The loss of active sodium ions has become one of the most critical issues restricting the large-scale application of sodium-ion batteries. Pre-sodium technology introduces additional active sodium ions to compensate for irreversible loss, thereby maximizing the release of battery energy density. The positive electrode sodium replenishment method is a commonly used pre-sodium method. During the first charge, the sodium replenishment agent in the positive electrode undergoes electrochemical oxidation and decomposition, releasing excess active sodium ions, which irreversibly migrate to the electrolyte and negative electrode, thus increasing the active sodium ion content during cycling and improving the overall energy density of the battery. Sodium carbonate, as a positive electrode sodium replenishment agent, has a theoretically high specific capacity (505 mAh·g). -1 Sodium carbonate has advantages such as low price, safety, non-toxicity, and stable properties; however, as a very poor conductor of electrons and ions, it has a wide decomposition bandgap of 2.52 eV, resulting in a high decomposition voltage, low decomposition efficiency, and an actual decomposition capacity of only 21 mAh g. -1 Furthermore, it can decompose in small amounts during repeated cycles, which seriously hinders its application in actual industrial production (Chem. Mater. 2017, 29, 14, 5948-5956).

[0003] Currently, in the field of pre-sodium, the main approach to applying sodium carbonate is to catalyze it using carbon or transition metal oxides that are not electrochemically active. In sodium-ion capacitors, researchers have reduced the sodium carbonate decomposition voltage to 4.25V and increased the first-cycle decomposition rate to 82.6% by mixing sodium carbonate, activated carbon, and conductive carbon in a 4:4:1 ratio; however, excessively high carbon content leads to a significant decrease in its volumetric capacitance, limiting its application as a cathode additive (J. Powder Sources, 2021, 515, 230628).

[0004] Existing technologies propose combining sodium carbonate with different carbon materials to reduce the decomposition voltage of sodium carbonate; however, these processes are too cumbersome and not conducive to scaling up industrial production. Other existing technologies use composite materials of sodium carbonate, metal oxides, and carbon to leverage some of the electrochemical activity of sodium carbonate; however, the use of large amounts of metal oxides results in excessively high levels of inactive substances remaining after the sodium replenishment process, which is detrimental to the stable cycling of the battery. Summary of the Invention

[0005] This invention provides a composite sodium supplement agent, its preparation method, and its application, to solve the problems of cumbersome process and low battery stability in the prior art when using sodium carbonate as a sodium supplement agent.

[0006] In a first aspect, the present invention provides a composite sodium supplement composed of sodium-ion battery layered oxide and sodium carbonate in a mass ratio of 1:0.1 to 10.

[0007] As one possible implementation, the particle size of the composite sodium supplement is less than 5 μm.

[0008] As one possible implementation, the chemical formula of the sodium-ion battery layered oxide is Na. x TMO2, where 0.1≤x<1, and TM is one or a combination of several of Ca, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Mg, and Li.

[0009] In a second aspect, the present invention provides a method for preparing a compound sodium supplement, comprising the following steps: mixing the raw material components in proportion according to the formulation components of the compound sodium supplement as described in any possible implementation of the first aspect, and then grinding them to obtain the compound sodium supplement.

[0010] As one possible implementation, the grinding step includes: adding grinding balls in a sealed ball mill and grinding at 200–700 rpm·min. -1 Ball milling at a rotation speed of 10–70 h.

[0011] Thirdly, the present invention provides the application of the composite sodium supplement agent described in any possible implementation of the first aspect or the composite sodium supplement agent prepared by the preparation method described in any possible implementation of the second aspect in the preparation of sodium-ion batteries.

[0012] Fourthly, the present invention provides a sodium-ion battery, wherein the positive electrode active material comprises the composite sodium supplement agent described in any possible implementation of the first aspect or the composite sodium supplement agent prepared by the preparation method described in any possible implementation of the second aspect.

[0013] As one possible implementation, the mass of the composite sodium supplement is 0.1 wt% to 20 wt% of the mass of the positive electrode active material.

[0014] As one possible implementation, the positive electrode active material also includes one or a combination of several of the following: sodium-ion battery layered oxides, polyanionic compounds, Prussian blue, and Prussian blue analogues.

[0015] As one possible implementation, the preparation method includes the following steps: mixing the active material with a conductive agent and a binder to prepare a slurry, and coating it onto a current collector; performing drying and slicing operations in sequence to prepare a positive electrode sheet; and assembling the sodium-ion battery using the positive electrode sheet as the positive electrode and sodium as the negative electrode.

[0016] Sodium carbonate has a high theoretical specific capacity, but its electrochemical decomposition potential is too high, making it difficult to directly apply in pre-sodium supplementation. Layered oxides, when used alone as positive electrode sodium supplements, leave behind inactive substances. The composite sodium supplement provided by this invention, by combining sodium carbonate with layered oxides, effectively reduces the decomposition voltage of sodium carbonate and improves its decomposition efficiency. The composite sodium supplement maintains the electrochemical activity of sodium carbonate while leaving less inactive residue after sodium removal. In the composite sodium supplement provided by this invention, both sodium carbonate and layered oxides can release active sodium ions, and the introduction of inactive carbon is avoided, thus improving the volumetric specific capacity of the sodium supplement. This constructs a highly efficient composite pre-sodium system that exhibits excellent sodium supplementation performance, effectively replenishing the irreversible capacity loss of active sodium ions in full cells and improving the battery's energy density.

[0017] The method for preparing the composite sodium supplement provided by the present invention involves mixing sodium carbonate with layered oxides through mechanical ball milling to obtain a composite sodium supplement. The preparation method is simple and easy to operate, and is environmentally friendly and pollution-free, making it suitable for large-scale production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a SEM image of untreated sodium carbonate provided in an embodiment of the present invention.

[0020] Figure 2 The image shown is a SEM image of product H provided in an embodiment of the present invention.

[0021] Figure 3The first five charge-discharge curves of product D provided in this embodiment of the invention.

[0022] Figure 4 The charge-discharge curves of the experimental and control group batteries provided in the embodiments of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] To address the problems of cumbersome processes and low battery stability associated with using sodium carbonate as a sodium supplement in existing technologies, this invention provides a composite sodium supplement and its preparation method.

[0025] The composite sodium replenisher provided by this invention effectively reduces the decomposition voltage of sodium carbonate and improves its decomposition efficiency by combining sodium carbonate with layered oxides. The composite sodium replenisher not only maintains the electrochemical activity of sodium carbonate but also leaves less inactive residue after sodium removal. Both sodium carbonate and layered oxides in the composite sodium replenisher can release active sodium ions, while avoiding the introduction of inactive carbon, thus improving the volumetric specific capacity of the sodium replenisher. This constructs a highly efficient composite pre-sodium system that exhibits excellent sodium replenishment performance and can effectively compensate for the irreversible capacity loss of active sodium ions in full cells.

[0026] Furthermore, in the preparation of the composite sodium supplement provided by this invention, comparative experiments were also conducted on the selection of sodium salts. The results showed that only when sodium carbonate is combined with layered oxides can the sodium supplement achieve the desired effect. Other sodium salts, even sodium oxalate with the same carbon and oxygen anionic elemental composition, do not produce ideal sodium supplements when combined with layered oxides. It is evident that sodium carbonate combined with layered oxides in this invention plays an irreplaceable role.

[0027] Furthermore, the present invention provides an electrochemical performance test experiment of the composite sodium supplement, which verifies that the composite sodium supplement provided by the present invention has better capacity and electrochemical performance in application, and exerts a better sodium supplementation effect.

[0028] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0029] Example 1

[0030] This embodiment provides an experimental preparation of a compound sodium supplement.

[0031] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 9:1 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm·min. -1 The product A was obtained by ball milling at a certain speed for 20 hours.

[0032] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 8:2 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm·min. -1 Ball milling at a certain speed for 20 hours yielded product B.

[0033] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 7:3 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm. -1 The product C was obtained by ball milling at a certain speed for 20 hours.

[0034] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 6:4 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm·min. -1 The product D was obtained by ball milling at a certain speed for 20 hours.

[0035] Sodium carbonate and NaCrO2 were mixed in a 5:5 mass ratio and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm·min. -1 The product E was obtained by ball milling at a certain speed for 20 hours.

[0036] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 6:4 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 200 rpm. -1 The product F was obtained by ball milling at a certain speed for 20 hours.

[0037] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 6:4 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 700 rpm. -1 The product G was obtained by ball milling at a certain speed for 20 hours.

[0038] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 6:4 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm·min. -1 The product H was obtained by ball milling at a certain speed for 10 hours.

[0039] Sodium carbonate and NaCrO2 were mixed in a mass ratio of 6:4 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed and milled at 300 rpm·min. -1 The product I was obtained by ball milling at a certain speed for 70 hours.

[0040] Sodium carbonate and Na(Fe) in a mass ratio of 6:4 1 / 3 Ni 1 / 3Mn 1 / 3 Mix O2 and place it in a ball mill jar. Add the grinding beads and seal the jar. Mill at 300 rpm. -1 The product J was obtained by ball milling at a certain speed for 20 hours.

[0041] Sodium carbonate and conductive carbon were mixed in a mass ratio of 6:4 and placed in a ball mill jar. After adding grinding beads, the ball mill jar was sealed, and the mixture was milled at 300 rpm. -1 The product K was obtained by ball milling at a certain speed for 20 hours.

[0042] Untreated pure sodium chromate powder was used as product L.

[0043] Scanning electron microscopy analysis of unmilled sodium carbonate yielded the following results: Figure 1 The SEM image shown; scanning electron microscopy analysis of product D yielded the following results. Figure 2 The SEM image shown.

[0044] contrast Figure 1 and Figure 2 It can be seen that ball milling significantly reduces the particle size of sodium carbonate, which helps to accelerate the migration of ions and electrons in the electrochemical decomposition process and significantly improves its kinetics.

[0045] Example 2

[0046] This embodiment provides an electrochemical performance test experiment for a composite sodium supplement.

[0047] The sodium supplement, conductive agent, and binder to be tested were mixed and ground in a mass ratio of 8:1:1, and then solvent was added and stirred to form a uniform slurry. The slurry was coated onto the current collector and dried in a vacuum drying oven at 110℃ for 12 hours. The dried material was then cut into 12mm diameter discs, which are the positive electrode sheets. Using the positive electrode sheet as the positive electrode, metallic sodium as the negative electrode, and glass fiber as the separator, 1 mol·L⁻¹... -1 NaClO4 (EC:PC = 1:1, with 5% FEC) was used as the electrolyte to assemble coin cells.

[0048] In this embodiment, KB was used as a conductive agent, PVDF as a binder, NMP as a solvent, and aluminum foil as a current collector. Products A through K prepared in Example 1 were used as sodium supplements to prepare batteries A through K. Within a voltage range of 2.0–4.2V (2.0–4.6V for battery K), a 45mAh·g... -1 Charge-discharge tests were conducted using the current density, and the results are shown in Table 1. Figure 3 The battery electrochemical performance results are shown.

[0049] Table 1. Decomposition voltage and decomposition capacity of compound sodium supplement

[0050]

[0051] Table 1 shows that ball milling the mixture of sodium carbonate and layered oxides effectively promotes the electrochemical decomposition of sodium carbonate and reduces its decomposition voltage. Therefore, the composite sodium supplement exhibits higher capacity during the first charging cycle. Meanwhile, layered oxides, represented by sodium chromate, leave behind non-electrochemically active solids (such as Na₂O₃) after decomposition. 1-x The compound sodium supplement provided by this invention produces less solid residue after decomposition (CrO2), while the decomposition product of sodium carbonate is only carbon dioxide gas. This is beneficial to battery stability. Figure 3 It is known that the compound sodium supplement can irreversibly release a large number of active sodium ions during the first charge cycle, while only a small number of sodium ions are inserted during the discharge process, which is beneficial for replenishing the consumption of active sodium ions.

[0052] Example 3

[0053] This embodiment provides a verification experiment on the effect of composite sodium supplement on the charging and discharging performance of batteries.

[0054] The positive electrode active material, conductive agent, and binder are mixed and ground in a mass ratio of 8:1:1. A solvent is added and stirred to form a uniform slurry. This slurry is coated onto the positive electrode current collector and dried in a vacuum drying oven at 110℃ for 12 hours. The resulting material is then cut into 12mm diameter discs, which are the positive electrode sheets. Similarly, hard carbon, conductive agent, and binder are mixed and ground in a mass ratio of 90:5:5. A solvent is added and stirred to form a uniform slurry. This slurry is coated onto the negative electrode current collector and dried in a vacuum drying oven at 80℃ for 12 hours. The resulting material is then cut into 12mm diameter discs, which are the negative electrode sheets. Using the positive electrode sheet as the positive electrode, the negative electrode sheet as the negative electrode, and glass fiber as the separator, 1 mol·L⁻¹... -1 NaClO4 (EC:PC = 1:1, with 5% FEC) was used as the electrolyte to assemble coin cells.

[0055] In this embodiment, SP is used as the conductive agent, PVDF as the binder, NMP as the solvent, aluminum foil as the positive current collector, copper foil as the negative current collector, and Na(Fe) as the conductive agent. 1 / 3 Ni 1 / 3 Mn 1 / 3 A mixture of O2 and product D obtained in Example 1 (product D being 5 wt% of the mixture) was used as the positive electrode active material in the experimental group to prepare the experimental group battery; Na(Fe) 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 was used as the positive electrode active material in the control group to prepare a control group battery. Within the voltage range of 2.0–4.5 V, at a concentration of 15 mAh / g... -1 After activation at a current density of 3 cycles, charge-discharge cycles were performed in the voltage range of 2.0–4.0V to obtain the following results: Figure 4 And the charge / discharge capacity shown in Table 2.

[0056] Table 2 Charge / Discharge Capacity

[0057]

[0058] From Table 2 and Figure 4 It is evident that product D can release excess active sodium ions in the full cell, demonstrating excellent sodium replenishment effect in practical applications.

[0059] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0060] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A compound sodium supplement, characterized in that, It consists of sodium-ion battery layered oxide and sodium carbonate in a mass ratio of 1:0.1 to 10; The chemical formula of the sodium-ion battery layered oxide is Na. x TMO2, where 0.1≤x<1, and TM is one or a combination of several of Li, Mg, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, and Sn.

2. The compound sodium supplement according to claim 1, characterized in that, Its particle size is less than 5μm.

3. A method for preparing a compound sodium supplement, characterized in that, Includes the following steps: The compound sodium supplement is prepared by mixing the raw material components in proportion according to any one of claims 1 to 2 and then grinding them to obtain the compound sodium supplement.

4. The preparation method according to claim 3, characterized in that, The grinding step includes: adding grinding balls to a sealed ball mill and grinding at 200–700 rpm·min. -1 Ball milling at a rotation speed of 10–70 h.

5. The application of the composite sodium supplement agent according to any one of claims 1 to 2 or the composite sodium supplement agent prepared by the preparation method according to any one of claims 3 to 4 in the preparation of sodium-ion batteries.

6. A sodium-ion battery, characterized in that, Its positive electrode raw material includes an active material, which includes the composite sodium supplement as described in any one of claims 1 to 2 or the composite sodium supplement prepared by the preparation method described in any one of claims 3 to 4.

7. The sodium-ion battery according to claim 6, characterized in that, The mass of the compound sodium supplement is 0.1 wt% to 20 wt% of the mass of the active material.

8. The sodium-ion battery according to claim 6, characterized in that, The active material also includes one of sodium-ion battery layered oxides, polyanionic compounds, Prussian blue, and Prussian blue analogues.

9. The method for preparing a sodium-ion battery according to any one of claims 6 to 8, characterized in that, Includes the following steps: The active material is mixed with a conductive agent and a binder to prepare a slurry, which is then coated onto the current collector. The positive electrode sheet was prepared by sequentially drying and slicing operations. The sodium-ion battery is assembled using the positive electrode as the positive electrode and sodium as the negative electrode.

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