A sodium supplement additive for sodium-ion batteries and a preparation method and application thereof

Abstract

This invention discloses a sodium-ion battery additive, its preparation method, and its application, belonging to the field of sodium-ion battery technology. The invention first prepares a precursor using a high-temperature solid-state method. During the synthesis of the precursor, a transition metal is oxidized from a low-valence state to a high-valence state, providing a basic crystal framework for the subsequent synthesis of the sodium-ion battery additive, ensuring that no impurity phases are generated in the additive. The precursor is then used to prepare the sodium-ion battery additive, introducing Na during this process. 2 O 2 During sintering, decomposition releases oxygen, ensuring an oxidizing atmosphere inside the sealed crucible and maintaining Ni. 3+ The sodium-ion battery has a stable valence state. The sodium-ion additive prepared by this invention has a lower decomposition voltage and a higher irreversible specific capacity. Therefore, adding a small amount of sodium-ion additive to the positive electrode of a sodium-ion battery can provide more additional capacity, thereby significantly improving the energy density of the sodium-ion battery.

Description

A sodium-ion battery sodium supplement additive, its preparation method and application Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a sodium-ion battery additive, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in daily production due to their high energy density and long cycle life. However, because the reserves of lithium carbonate, the main lithium resource for lithium-ion batteries, in the Earth's crust are insufficient, researching sodium-ion battery technology to replace lithium-ion batteries and alleviate over-reliance on scarce lithium resources is of great significance for ensuring energy security and achieving carbon neutrality. Pre-sodiumification technology is highly effective in reducing the impact of SEI formation on the energy density of sodium-ion full batteries. By pre-storing additional sodium ions in the positive or negative electrode, the active sodium source consumed in the initial SEI formation is compensated. Furthermore, during subsequent charge and discharge processes, the sodium pre-stored in the positive or negative electrode can continuously compensate for the sodium ion consumption caused by SEI formation, thereby extending the cycle life of the full battery.

[0003] Currently, pre-sodiumization can be broadly categorized into four methods: direct pre-impregnation, chemical sodiumization, electrochemical pre-sodiumization, and addition of cathode self-sacrificing agents.

[0004] 1. The direct pre-impregnation method prepares sodium-rich cathodes by mixing metallic sodium and active materials to compensate for sodium ions lost due to the synthesis of sodium-rich compounds in the anode. The disadvantage of this method is that it is selective in the type of cathode material, and can only preferentially select materials with large and numerous vacancy crystal structures such as NASICON. The sodium replenishment effect of other cathode materials is limited, and the direct use of sodium metal also poses certain dangers. Therefore, it cannot be applied to large-scale production.

[0005] 2. Chemical sodium conversion refers to providing additional endogenous sodium reserves through chemical methods to alleviate sodium loss caused by the negative electrode. The advantage of this method is that it does not affect the electrochemical structure of the battery, but it has obvious limitations and selectivity on the positive electrode material and is difficult to commercialize.

[0006] 3. Electrochemical pre-sodiumization involves pre-assembling a positive electrode half-cell using electrochemical methods and then discharging it to a low voltage to inject excess active sodium into the positive electrode material. Its advantage is that the degree of pre-sodiumization can be controlled by adjusting the discharge cutoff voltage. However, the complex process of assembling, disassembling, and reassembling the half-cell greatly reduces the feasibility of electrochemical pre-sodiumization in large-scale production.

[0007] 4. The positive electrode self-sacrificing agent addition method compensates for sodium loss caused by the formation of the SEI film on the negative electrode by adding a compound with high sodium content to the positive electrode, which irreversibly releases sodium ions during charging. Based on the characteristics of sodium-ion batteries, an ideal positive electrode sodium replenisher should have the following characteristics: 1. High sodium content, capable of replenishing more capacity with less sodium replenisher, ensuring an improvement in battery energy density; 2. Byproducts do not affect the battery's cycle performance; 3. Sodium removal potential lower than the full battery's charging cutoff voltage, thus adapting to most positive electrode materials; 4. Sufficient stability and compatibility with current processes, with the potential for commercial production. Currently studied sodium replenishers include Na2NiO2, Na2O2, NaN3, Na3P, NaNO2, Na2C2O4, Na2C4O4, and NaAc. However, these sodium replenishers often struggle to simultaneously achieve the dual advantages of high irreversible capacity and low decomposition voltage. For example, although Na2NiO2 can undergo sodium removal at lower voltages, it can only yield 300 mAh g at below 4 V. -1 The capacity is relatively low; although Na2C2O4 decomposes almost completely during charging, releasing 400 mAh g -1 While Na3P boasts high specific capacity, its decomposition voltage is as high as 4.2 V, making it unsuitable for most cathode materials. Although Na3P has a theoretically high specific capacity, its preparation requires sodium metal, making quantitative reactions difficult. Overall, obtaining a new sodium supplement agent with both high irreversible capacity and low decomposition voltage remains a pressing challenge. Summary of the Invention

[0008] This invention provides a sodium-replenishing additive for sodium-ion batteries, its preparation method, and its application. The sodium-replenishing additive is a sodium-rich transition metal oxide, which has the advantages of high capacity and low decomposition voltage. It can compensate for the sodium ions consumed in the first SEI cycle with a small amount of sodium-replenishing agent, thereby significantly improving the energy density of the whole battery.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A sodium-replenishing additive for sodium-ion batteries is a sodium-rich transition metal oxide with the chemical formula Na. x MO y Wherein, M is one or more of Ni, Co, Fe, Mn, Zn, Cr, Cu, Ge, and Zr; wherein, the average valence state of M in the sodium-supplementing additive is not higher than its highest oxidation state; x is 3~6, ​​and y is 2~4.

[0011] The sodium supplement is at least one of Na5MaO4, Na6MbO4, Na4McO4, and Na4MdO3, where Ma is at least one of Fe, Ni, Co, Mn, Ru, Ir, Sn, Cr, Nb, and Mo; Mb is at least one of Fe, Ni, Mg, Cu, Ba, Zn, Hg, and Ca; Mc is at least one of Fe, Ni, Ti, V, W, Mo, Mn, Zr, and Ge; and Md is at least one of Fe, Ni, Mg, Cu, Ba, Zn, Hg, and Ca.

[0012] A method for preparing a sodium-ion battery sodium supplement additive includes the following steps:

[0013] S1: Using Na2O as the sodium source and transition metal oxide as the transition metal source, Na2O and transition metal oxide are mixed in a certain proportion, ball-milled, and then calcined at high temperature to obtain a transition metal sodium oxide precursor. During the synthesis of the precursor, the low-valence transition metal is oxidized to a high-valence state, and a basic lattice framework is provided for the subsequent synthesis of sodium-supplementing additives, so that no impurity phases are generated in the sodium-supplementing additives.

[0014] S2: The precursor is mixed with sodium oxide, heated to 550℃ at 5℃ / min in an argon atmosphere and held for 48 hours, then naturally cooled to room temperature to obtain the sodium additive. The selected sodium oxide has a Na2O purity of 80% and contains 20% Na2O2, which will decompose and release oxygen during sintering, ensuring an oxidizing atmosphere inside the sealed crucible and maintaining Ni. 3+ The valence state is stable; the introduction of Na2O2 avoids the use of oxygen, a combustion-supporting gas, during the sintering process and ensures a uniform reducing atmosphere; compared with directly introducing O2, this method avoids the safety issues caused by the combustion-supporting gas O2.

[0015] The aforementioned sodium-supplementing additive is used in the composite cathode of sodium-ion batteries, wherein the sodium-supplementing additive accounts for a mass percentage of more than 5 wt% and less than 30 wt% of the composite cathode.

[0016] Beneficial Effects: This invention provides a sodium-replenishing additive for sodium-ion batteries, its preparation method, and its application. The sodium-replenishing additive is prepared via a high-temperature solid-state method. In the preparation process, a precursor is first prepared. During the synthesis of the precursor, a low-valence transition metal is oxidized to a high-valence state, providing a basic crystal framework for the subsequent synthesis of the sodium-replenishing agent. This effectively reduces the sintering time of the subsequent reaction and ensures sufficient sintering, preventing the formation of impurity phases in the sodium-replenishing additive. The precursor is then mixed with sodium oxide and calcined to generate the sodium-replenishing additive. No additional oxidizing gas is required during the calcination process. The prepared sodium-replenishing additive, Na... x MO yWith lower decomposition voltage and higher irreversible specific capacity, adding a small amount of Na to the cathode of a sodium-ion battery is beneficial. x MO y This allows for the provision of additional capacity, thus significantly improving the energy density of sodium-ion batteries. Adding sodium-based additives to the MFN cathode and assembling it with a hard carbon anode to form a half-cell resulted in a 22.5 mAh g⁻¹ increase in the specific capacity of the full cell after 100 cycles at 0.33 C. -1 The energy density increased by 25.23%. Attached Figure Description

[0017] Figure 1 is an X-ray diffraction (XRD) pattern of Na5NiO4 in an embodiment of the present invention;

[0018] Figure 2 is a scanning electron microscope (SEM) image of Na5NiO4 in an embodiment of the present invention;

[0019] Figure 3 shows the first charge-discharge curve of the Na|| Na5NiO4 half-cell at 0.1C in the embodiment of the present invention;

[0020] Figure 4 shows the first charge-discharge curves of the HC||MFN and HC||MFN+10% Na5NiO4 full cells in the embodiments of the present invention;

[0021] Figure 5 shows the cycle stability curves of the HC||MFN and HC||MFN+10% Na5NiO4 full cells in the embodiments of the present invention. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0023] Example 1

[0024] The sodium-rich transition metal oxide sodium supplementer is prepared by a high-temperature solid-state method, specifically including the following steps:

[0025] Using Na₂O as the sodium source and NiO as the nickel source, Na₂O and NiO were mixed at a molar ratio of 1:1 and ball-milled at 450 rpm for 2 hours using a planetary ball mill. The powder was then placed in an oxygen furnace and heated to 650°C at a rate of 5°C / min, and held at that temperature for 14 hours. After cooling, the NaNiO₂ precursor was obtained. During the synthesis of the precursor, Ni… 2+ Oxidized to Ni 3+ It provides a basic lattice framework for the subsequent synthesis of sodium supplement, which can effectively reduce the sintering time of subsequent reactions and ensure sufficient subsequent sintering, so that no impurity phases are generated in Na5NiO4.

[0026] Na₂O and NaNiO₂ precursors were hand-milled at a ratio of 2.2:1 for 30 minutes. The mixed powder was then pressed into tablets using a tablet press at a pressure of 20 MPa. The tablets were placed in a sealed corundum crucible and then placed in a tube furnace. The furnace was heated to 550°C at a rate of 5°C / min and held at that temperature for 48 hours in an argon atmosphere. After natural cooling to room temperature, Na₅NiO₄ sodium-supplementing material was obtained. The selected Na₂O had a purity of 80% and contained 20% Na₂O₂. During sintering, Na₂O decomposed and released oxygen, ensuring an oxidizing atmosphere inside the sealed crucible to maintain the Ni content. 3+ The valence state is stable. The introduction of Na2O2 avoids the use of oxygen, a combustion-supporting gas, during the sintering process and ensures a uniform reducing atmosphere.

[0027] The phase composition of Na5NiO4 was analyzed by X-ray diffraction (XRD). The diffraction pattern was recorded by stepwise scanning 2θ from 10° to 80° at room temperature. As shown in Figure 1, Na5NiO4 and PDF#70-0734 have the same characteristic peaks, indicating that Na5NiO4 is a pure phase and has no other impurities.

[0028] The microstructure of Na5NiO4 was determined using scanning electron microscopy (SEM) with an accelerating voltage of 5 kV. The SEM image of synthesized Na5NiO4 is shown in Figure 2. The microstructure of the sintered Na5NiO4 consists of micron-sized columnar particles, indicating that the Na5NiO4 has a small and stable particle size, thus exhibiting low electrochemical polarization.

[0029] Example 2

[0030] In a glove box, the Na5NiO4 positive electrode sodium supplementation additive (85wt%) and conductive carbon black Ketjen black (10wt%) prepared in Example 1 were mixed in a mortar and ground thoroughly for 30 minutes to make them uniform. Then, PTFE (5wt%) was added and mechanically mixed until the solid powder was fully bonded into a sheet. The sheet was then transferred to a roller press and repeatedly rolled until the thick electrode sheet became a uniform thin electrode sheet with a thickness of about 100μm. The thin electrode sheet was cut into a circular battery positive electrode sheet with a diameter of 12mm to obtain a sodium-ion battery composite positive electrode sheet.

[0031] Half-cell assembly: Using the aforementioned positive electrode sheet as the positive electrode, a 14mm diameter sodium metal disc as the negative electrode sheet, and a 19mm diameter aluminum foil placed in the positive electrode shell as the positive current collector, a circular positive electrode sheet is placed in the center of the positive electrode shell, and 75μL of 1 mol NaPF6 in PC with 2% FEC electrolyte is added. A glass fiber separator is then placed, and 75μL of electrolyte is added to fully wet the separator. Finally, a hard carbon negative electrode, a gasket, a spring contact, and the negative electrode shell are placed in sequence. The assembled coin cell sodium-ion battery is then sealed using a packaging machine and allowed to stand for 12 hours before electrochemical testing.

[0032] The first charge-discharge test of the Na||Na5NiO4 half-cell was conducted at a temperature of 25℃, a voltage range of 2-4.5V, and a rate of 0.1C. As shown in Figure 3, the specific capacity of the Na||Na5NiO4 half-cell during the first charge cycle was 537 mAh g. -1 The discharge specific capacity is 2mAhg. -1 The average decomposition voltage is 3V, which demonstrates the dual advantages of Na5NiO4: high irreversible capacity and low sodium removal voltage.

[0033] Example 3

[0034] Preparation of the positive electrode sheet. In a glove box, MFN sodium battery positive electrode material (80wt%), conductive carbon black Ketjen black (10wt%), and Na5NiO4 sodium supplement material (10wt%) are mixed in a mortar and ground thoroughly for 30 minutes to ensure uniform mixing. Then, PTFE (5wt%) is added and grinding continues until the solid powder is fully bonded into a sheet. The sheet is then transferred to a roller press and repeatedly rolled until the thick electrode sheet becomes a uniform thin electrode sheet with a thickness of approximately 100μm. The sheet is then cut into circular battery positive electrode sheets with a diameter of 12mm to obtain the sodium-ion battery positive electrode sheet.

[0035] Assembly of the full battery: Using the above-mentioned positive electrode sheet as the positive electrode, a mixture of hard carbon, binder (polyvinylidene fluoride PVDF), and Super P (85:8:7) was uniformly coated onto a single-sided carbon-coated aluminum foil. After vacuum drying at 110℃, it was cut into 14mm diameter circular pieces as negative electrode sheets. A 19mm diameter aluminum foil was placed in the positive electrode shell, and the circular positive electrode sheet was placed in the center of the positive electrode shell. 75μL of 1 mol NaPF6 in PC with 2% FEC electrolyte was added, followed by the placement of a glass fiber separator and the addition of 75μL of electrolyte to fully wet the separator. Finally, the hard carbon negative electrode, gasket, spring sheet, and negative electrode shell were placed in sequence. The assembled coin cell sodium-ion battery was then sealed using a packaging machine and subjected to electrochemical testing after standing for 12 hours.

[0036] For HC (hard carbon) || MFN (NaNi) 0.33Fe 0.33 Mn 0.33 The first charge-discharge cycle of the O2) and HC||MFN+10% Na5NiO4 full cells was conducted at 25℃ and within a voltage range of 1.2-4.0V. After activation at 0.1C for 3 cycles, a long electrochemical cycle at 0.33C was performed. As shown in Figure 4, the first discharge specific capacity of the HC||MFN full cell was 111 mAh g. -1 The initial discharge specific capacity of HC||MFN+10%Na5NiO4 is 146mAh g. -1 This indicates that the Na5NiO4 cathode sodium supplementation additive played a role, compensating for the active sodium ions consumed in the formation of SEI in the full cell and improving the first-cycle discharge capacity.

[0037] Long-term cycling performance tests were conducted on HC||MFN and HC||MFN+10% Na5NiO4 full cells. The test temperature was 25℃, the voltage range was 1.2-4.0V, the first three cycles were at a rate of 0.1C, and the subsequent cycles were at a rate of 0.33C. As shown in Figure 5, after 100 cycles at 0.1-0.33C, the specific capacity of the full cell with 10% sodium supplementation increased significantly by 22.5%. Compared with the full cell without sodium supplementation, its capacity retention rate remained consistent, indicating that the addition of sodium supplementation did not affect the cycling performance of the full cell. This suggests that the HC||MFN+10% Na5NiO4 full cell has good cycling stability, and the Na5NiO4 sodium supplementation is well-suited to the MFN system.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a sodium-ion battery sodium supplement additive, characterized in that, Includes the following steps: S1: Using Na2O as the sodium source and transition metal oxide as the transition metal source, Na2O and transition metal oxide are mixed at a molar ratio of 1:1, ball-milled, and then calcined at high temperature to obtain a transition metal sodium oxide precursor. During the synthesis of the precursor, the low-valence transition metal is oxidized to a high-valence state, and a basic lattice framework is provided for the subsequent synthesis of sodium supplementation agent, so that no impurity phase is generated in the sodium supplementation additive; S2: The precursor is mixed with sodium oxide and calcined in an argon atmosphere to obtain a sodium supplementation additive, wherein the sodium oxide is composed of 80% Na2O and 20% Na2O2.

2. The method for preparing the sodium-replenishing additive for sodium-ion batteries according to claim 1, characterized in that, The high-temperature calcination process in S1 is as follows: the temperature is increased to 650℃ in an oxidizing atmosphere at a heating rate of 5℃ / min and held for 14 h. After cooling, the precursor is obtained.

3. The method for preparing the sodium-replenishing additive for sodium-ion batteries according to claim 1, characterized in that, The calcination process in S2 is as follows: the temperature is increased to 550℃ at 5℃ / min in an argon atmosphere and held for 48 hours, and then naturally cooled to room temperature to obtain the sodium supplement additive.

4. The sodium-replenishing additive for sodium-ion batteries prepared by the method according to any one of claims 1-3, characterized in that, The sodium supplement is at least one of Na5MaO4, Na6MbO4, Na4McO4, and Na4MdO3; Ma is at least one of Fe, Ni, Co, Mn, Ru, Ir, Sn, Cr, Nb, and Mo; Mb is at least one of Fe, Ni, Mg, Cu, Ba, Zn, Hg, and Ca; Mc is at least one of Fe, Ni, Ti, V, W, Mo, Mn, Zr, and Ge; and Md is at least one of Fe, Ni, Mg, Cu, Ba, Zn, Hg, and Ca.

5. The sodium-replenishing additive for sodium-ion batteries according to claim 4, characterized in that, The sodium supplement has a microstructure of columnar particles at the micrometer level.

6. The sodium-replenishing additive for sodium-ion batteries according to claim 4 or 5, characterized in that, The sodium supplement is Na5NiO4.

7. The application of the sodium-ion battery sodium supplementation additive as described in claim 1, characterized in that, The sodium-supplementing additive is used in the positive electrode of a sodium-ion battery, and the sodium-supplementing additive accounts for a mass percentage of the positive electrode that is greater than 5 wt% and less than 30 wt%.

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