Application of a sodium-ion battery functional additive and sodium-ion battery

Abstract

The application belongs to the technical field of sodium ion batteries, and discloses application of a functional additive of a sodium ion battery and the sodium ion battery; the functional additive is added and dissolved into an electrolyte of the sodium ion battery; the functional additive is a metal ion inorganic salt; and the sodium ion battery takes a Prussian blue material as a positive active material; in the charging and discharging process of the obtained sodium ion battery, cations in the functional additive can reduce water content in a framework and stabilize the framework structure, thereby promoting sodium ion transmission, protecting the pole piece from side reactions with the electrolyte, and further improving the cycle and rate performance of the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically, it relates to the application of a sodium-ion battery functional additive and sodium-ion batteries. Background Technology

[0002] In the late 1970s, research on sodium-ion batteries began almost simultaneously with that on lithium-ion batteries. However, due to the limitations in energy density and cycle performance faced by sodium-ion batteries at the time, lithium-ion batteries received more attention. In recent years, as problems such as the scarcity, uneven distribution, and difficulties in the development and utilization of lithium resources have gradually become apparent, the search for low-cost, abundant alternatives has become a focus. Among candidate batteries, sodium-ion batteries have returned to the forefront due to their abundant and uniform distribution of sodium resources, low cost, and low cost fluctuations. Combined with a wide temperature range and high safety attributes, sodium-ion batteries are expected to play a significant role in the energy storage field.

[0003] The cathode, as a crucial component of a battery, is of paramount importance, largely determining the battery's energy density and cycle life. Thanks to its open framework structure, abundant redox active sites, and strong structural stability, Prussian blue analogue (PBA) materials are among the most ideal cathode materials for sodium-ion batteries. Its structural formula can generally be represented as A. x M A [M B (CN)6] (1 -y)·□ y ·nH₂O. Where A is an alkali metal or alkaline earth metal cation, M... A M B It is a transition metal cation, which can be selected from one or more of Mn, Fe, Co, Ni, Cu, Zn, etc., □ is M B (CN)6 empty holes, 0 <x<2,0≤y<1。

[0004] When sodium-ion batteries are charged and discharged, alkali metal or alkaline earth metal cations are extracted and inserted into the three-dimensional framework structure of polyalkali metal ions (PBA). During this process, the three-dimensional framework structure of PBA must remain stable for the sodium-ion battery to have a stable cycle life. However, the insertion and extraction of alkali metal or alkaline earth metal cations inevitably causes slight changes in the lattice constant of PBA, especially when two transition metals in PBA undergo simultaneous valence changes. Due to the water synthesis environment and the rapid precipitation of PBA, a certain amount of water (including absorbed water, interstitial water, and coordination water) exists in the structure, which is considered a serious defect of PBA. When the water content in the PBA structure is high, Na ions interact strongly with the water in the framework during the insertion and extraction process, leading to M... A -CN-M BThe structural damage further exacerbates the collapse of the PBA three-dimensional framework. Therefore, PBA materials with high water content and simultaneous valence changes of two transition metals often exhibit poor cycle stability, resulting in a shorter cycle life for sodium-ion batteries.

[0005] In Prussian blue-type cathode materials, pore water within the crystal structure readily forms hydrogen bonds with coordinated water, increasing the difficulty of removing it. If the pore water is not completely removed, it occupies part of the space within the crystal structure, hindering the removal of alkali metal or alkaline earth metal ions (such as Na+). + The transmission of pore water is affected. If the pore water is not completely removed, it will be released along with Na ions during the charging and discharging process, ionize into the electrolyte, and undergo side reactions, causing electrolyte consumption, increased impedance, and adverse consequences such as capacity decay and gas expansion in the electrochemical energy storage device.

[0006] In view of this, there is a need to provide a solution that can fundamentally solve the problems of unstable three-dimensional framework structure of PBA and excessive residual voids / crystallization water in the framework, thereby improving the cycle stability of sodium-ion batteries and the diffusion rate of Na ions. Summary of the Invention

[0007] In light of the several problems pointed out in the background art, the purpose of this invention is to provide an application of a functional additive for sodium-ion batteries and a sodium-ion battery. The functional additive is added to and dissolved in the basic electrolyte of a sodium-ion battery using Prussian blue and its analogues as positive electrode materials, which can improve the cycle performance and rate performance of the sodium-ion battery.

[0008] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0009] According to one aspect of the present invention, an application of a functional additive for sodium-ion batteries is provided, wherein the functional additive is added to and dissolved in the electrolyte of a sodium-ion battery, the sodium-ion battery using Prussian blue-like materials as positive electrode active materials;

[0010] The functional additive is a metal ion inorganic salt; its cation is K. + 、Rb + Cs + Be 2+ Mg 2+ Ca 2+ 、Sr 2+ Ba 2+ Pb 2+ Al 3+ Ti 3+ ,Sc 3+ Y 3+ At least one of the following; its anion is PF6. -ClO4 - BF4 - FSI - TFSI - CF3SO3 - AlCl4 - FeCl4 - BCl4 - POF4 - AsF6 - SbF6 - At least one of them.

[0011] Furthermore, the content of the functional additive is 2% to 40% of the total mass of the electrolyte.

[0012] Preferably, the content of the functional additive is 6% to 20% of the total mass of the electrolyte.

[0013] Furthermore, the functional additive is at least one of barium perchlorate, barium hexafluorophosphate, strontium perchlorate, and potassium perchlorate.

[0014] Furthermore, the molecular formula of the Prussian blue-like material is A. x M A [M B (CN)6] (1-y) ·□ y ·nH₂O; where A is an alkali metal or alkaline earth metal cation, M A M B It is a transition metal cation, □ is M B (CN)6 empty holes, 0 <x<2,0≤y<1。

[0015] Furthermore, the electrolyte comprises a non-aqueous organic solvent and a sodium salt dissolved in the non-aqueous organic solvent.

[0016] Furthermore, the non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, ethyl methanesulfonate, dimethyl sulfite, and diethyl sulfite.

[0017] Furthermore, the sodium salt is selected from at least one of sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonate).

[0018] According to another aspect of the present invention, a sodium-ion battery is provided, wherein a Prussian blue-like material is used as the positive electrode active material; a functional additive is added to the electrolyte of the sodium-ion battery, wherein the functional additive is a metal ion inorganic salt; and its cation is K.+ 、Rb + Cs + Be 2+ Mg 2+ Ca 2+ 、Sr 2+ Ba 2+ Pb 2+ Al 3+ Ti 3+ ,Sc 3+ Y 3+ At least one of the following; its anion is PF6. - ClO4 - BF4 - FSI - TFSI - CF3SO3 - AlCl4 - FeCl4 - BCl4 - POF4 - AsF6 - SbF6 - At least one of them.

[0019] Furthermore, the content of the functional additive is 2% to 40% of the total mass of the electrolyte.

[0020] Preferably, the content of the functional additive is 6% to 20% of the total mass of the electrolyte.

[0021] Furthermore, the functional additive is at least one of barium perchlorate, barium hexafluorophosphate, strontium perchlorate, and potassium perchlorate.

[0022] Furthermore, the molecular formula of the Prussian blue-like material is A. x M A [M B (CN)6] (1-y) ·□ y ·nH₂O; where A is an alkali metal or alkaline earth metal cation, M A M B It is a transition metal cation, □ is M B (CN)6 empty holes, 0 <x<2,0≤y<1。

[0023] Furthermore, the electrolyte comprises a non-aqueous organic solvent and a sodium salt dissolved in the non-aqueous organic solvent.

[0024] Furthermore, the non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, ethyl methanesulfonate, dimethyl sulfite, and diethyl sulfite.

[0025] Furthermore, the sodium salt is selected from at least one of sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonate).

[0026] The beneficial effects of this invention are:

[0027] This invention provides a functional additive for sodium-ion batteries, which is added to and dissolved in the base electrolyte of the sodium-ion battery, and the sodium-ion battery uses Prussian blue and its analogues as the positive electrode material.

[0028] The cations in the functional additives preferentially insert into Prussian blue materials during the charging and discharging process of sodium-ion batteries, stabilizing the structure and minimizing the structural damage to Prussian blue materials during subsequent sodium ion insertion and extraction, thereby stabilizing the three-dimensional framework structure of Prussian blue materials.

[0029] Meanwhile, because the cations in the functional additives have a water-repellent effect, when hydrated Na(OH)2... + When ions attempt to enter the crystal lattice, the pre-embedded cations act as "guardians," allowing only bare sodium ions to enter. This provides sufficient space for the insertion / extraction of Na in the adjacent holes and for the diffusion of Na, as well as enough space and channels for the subsequent entry of Na. The insertion / extraction of bare sodium ions minimizes the damage to the frame caused by rapid ion shuttles, especially during high-rate charging and discharging, thereby avoiding the loss of battery performance and lifespan.

[0030] It is evident that during the charging and discharging process of sodium-ion batteries, the cations in the functional additives of this invention can reduce the water content in the framework and stabilize the framework structure, thereby promoting sodium ion transport, protecting the electrode from side reactions with the electrolyte, and thus improving the cycle and rate performance of sodium-ion batteries. Attached Figure Description

[0031] Figure 1 This is a comparison graph showing the cycle performance of sodium-ion batteries in Example 1 and Comparative Example 1;

[0032] Figure 2 This is a comparison graph showing the cycle performance of sodium-ion batteries in Example 3 and Comparative Example 1;

[0033] Figure 3 This is a comparison chart of the rate performance of sodium-ion batteries in Example 1 and Comparative Example 1;

[0034] Figure 4 This is a comparison chart of the rate performance of sodium-ion batteries in Example 3 and Comparative Example 1;

[0035] Figure 5 This is a SEM image of the electrode after multiple cycles in Comparative Example 1;

[0036] Figure 6 Here is a SEM image of the electrode after multiple cycles in Example 1;

[0037] Figure 7 This is a SEM image of the electrode after multiple cycles in Example 3. Detailed Implementation

[0038] To further understand the invention's content, features, and effects, the following embodiments are provided, along with detailed descriptions in conjunction with the accompanying drawings:

[0039] Example 1

[0040] 1. Preparation of positive electrode sheet

[0041] The positive electrode active material NaFe[Fe(CN)6], conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 70:20:10. The mixture was then coated onto an Al foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0042] 2. Preparation of electrolyte

[0043] Dissolve an appropriate amount of sodium perchlorate (NaClO4) in a non-aqueous organic solvent with a volume ratio of EC:DMC:FEC = 47.5:47.5:5 to prepare a NaClO4 electrolyte with a concentration of 1 mol / L. Then add 2% barium perchlorate to this electrolyte.

[0044] 3. Preparation of sodium-ion batteries

[0045] The sodium-ion battery of Example 1 was manufactured in the following order: negative electrode shell, sodium sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, and spring sheet.

[0046] Example 2

[0047] Sodium-ion batteries were prepared according to the method in Example 1, except that the amount of barium perchlorate added was 6%.

[0048] Example 3

[0049] Sodium-ion batteries were prepared according to the method in Example 1, except that the amount of barium perchlorate added was 10%.

[0050] Example 4

[0051] Sodium-ion batteries were prepared according to the method in Example 1, except that the amount of barium perchlorate added was 20%.

[0052] Example 5

[0053] Sodium-ion batteries were prepared according to the method in Example 1, except that the amount of barium perchlorate added was 40%.

[0054] Example 6

[0055] Sodium-ion batteries were prepared according to the method in Example 3, except that the sodium salt used in the electrolyte preparation process was NaPF6.

[0056] Example 7

[0057] Sodium-ion batteries were prepared according to the method in Example 3, except that the non-aqueous organic solvent in the electrolyte preparation process was EC:PC:FEC = 47.5:47.5:5 (volume ratio).

[0058] Example 8

[0059] Sodium-ion batteries were prepared according to the method in Example 3, except that the positive electrode active material used in the positive electrode preparation process was NaMn[Fe(CN)6].

[0060] Example 9

[0061] Sodium-ion batteries were prepared according to the method in Example 3, except that the functional additive used in the electrolyte preparation process was strontium perchlorate.

[0062] Example 10

[0063] Sodium-ion batteries were prepared according to the method in Example 3, except that the functional additive used in the electrolyte preparation process was potassium perchlorate.

[0064] Example 11

[0065] Sodium-ion batteries were prepared according to the method in Example 3, except that the functional additive used in the electrolyte preparation process was calcium perchlorate.

[0066] Example 12

[0067] Sodium-ion batteries were prepared according to the method in Example 3, except that the functional additive used in the electrolyte preparation process was aluminum perchlorate.

[0068] Example 13

[0069] Sodium-ion batteries were prepared according to the method in Example 3, except that the functional additive used in the electrolyte preparation process was barium hexafluorophosphate.

[0070] Example 14

[0071] Sodium-ion batteries were prepared according to the method in Example 3, except that the functional additive used in the electrolyte preparation process was strontium hexafluorophosphate.

[0072] Comparative Example 1

[0073] Sodium-ion batteries were prepared according to the method in Example 1, except that barium perchlorate, a functional additive, was not added during the electrolyte preparation process.

[0074] Comparative Example 2

[0075] Sodium-ion batteries were prepared according to the method in Example 1, except that no functional additive barium perchlorate was added during the electrolyte preparation process and the sodium salt used in the electrolyte preparation process was NaPF6.

[0076] Comparative Example 3

[0077] Sodium-ion batteries were prepared according to the method in Example 1, except that no functional additive barium perchlorate was added during the electrolyte preparation process and the organic solvent used in the electrolyte preparation process was EC:PC:FEC = 47.5:47.5:5 (volume ratio).

[0078] Comparative Example 4

[0079] Sodium-ion batteries were prepared according to the method in Example 1, except that no functional additive barium perchlorate was added during the electrolyte preparation process and the positive electrode active material during the positive electrode preparation process was NaMn[Fe(CN)6].

[0080] The cycle performance of the sodium-ion batteries prepared in all the above embodiments was tested as follows:

[0081] At room temperature, the sodium-ion batteries obtained in Examples 1-5 and Comparative Example 1 were charged at a constant current of 0.25C to a voltage of 4.0V, then allowed to stand for 1 minute, and discharged at a constant current of 0.25C to a voltage of 2.0V, and then allowed to stand for another 1 minute. This constitutes one cycle of charge and discharge.

[0082] The capacity retention rate (%) of a sodium-ion battery after n cycles = the discharge capacity of the sodium-ion battery in the nth cycle / the discharge capacity of the sodium-ion battery in the first cycle × 100%.

[0083] The following section describes the rate performance test of sodium-ion batteries.

[0084] At room temperature, the sodium-ion batteries obtained in Examples 1, 3, and Comparative Example 1 were charged to 4V at a constant current of 0.25C, then allowed to rest for 1 minute, and discharged to 2V at a constant current of 0.25C, followed by a rest for 1 minute, for a total of 5 cycles. Then, the sodium-ion batteries were charged to 4V at a constant current of 0.5C, then allowed to rest for 1 minute, and discharged to 2V at a constant current of 0.5C, followed by a rest for 1 minute, for a total of 5 cycles. Next, the sodium-ion batteries were charged to 4V at a constant current of 1C, then allowed to rest for 1 minute, and discharged to 2V at a constant current of 1C, followed by a rest for 1 minute, for a total of 5 cycles. Finally, the sodium-ion batteries were charged to 4V at a constant current of 1.5C, then allowed to rest for 1 minute, and discharged to 2V at a constant current of 1.5C, for a total of 5 cycles. After resting for 1 minute, repeat this cycle 5 times. Then, charge the sodium-ion battery to 4V at a constant current of 2C, then rest for 1 minute, discharge it to 2V at a constant current of 2C, then rest for 1 minute, repeat this cycle 5 times. Then, charge the sodium-ion battery to 4V at a constant current of 3C, then rest for 1 minute, discharge it to 2V at a constant current of 3C, then rest for 1 minute, repeat this cycle 5 times. Then, charge the sodium-ion battery to 4V at a constant current of 4C, then rest for 1 minute, discharge it to 2V at a constant current of 4C, then rest for 1 minute, repeat this cycle 5 times. Then, charge the sodium-ion battery to 4V at a constant current of 6C, then rest for 1 minute, discharge it to 2V at a constant current of 6C, then rest for 1 minute, repeat this cycle 5 times.

[0085] Capacity retention rate = discharge capacity in the last cycle / discharge capacity in the first cycle × 100%.

[0086] The parameters and cycle & rate performance test results of sodium-ion batteries in Examples 1-14 and Comparative Examples 1-3 are shown in Table 1.

[0087] Table 1. Sodium-ion battery parameters and cycle & rate performance test results for Examples 1-14 and Comparative Examples 1-3

[0088]

[0089]

[0090] As shown in Table 1, a comparison between Examples 1-5 and Comparative Example 1 reveals that adding different amounts of barium perchlorate additives to the electrolyte of sodium-ion batteries improves both cycle performance and rate performance to varying degrees. Preferably, the improvement is more pronounced when the content of the functional additive falls within the range of 6% to 20%.

[0091] As can be seen from the comparison of Examples 3, 9-12 in Table 1, adding the same amount of different cation types of additives to the electrolyte of sodium-ion batteries improved the cycle performance and rate performance to varying degrees. Preferably, the cation of the functional additive is Ba. 2+ 、Sr 2+ and K + The improvement is even more pronounced over time.

[0092] As can be seen from the comparison of Examples 13 and 14 and Comparative Example 2 in Table 1, the cycle performance and rate performance of sodium-ion batteries are improved to varying degrees after adding the same amount of different types of anion additives to the electrolyte of sodium-ion batteries.

[0093] As can be seen from the comparison between Example 6 and Comparative Example 2 in Table 1, after changing the sodium salt component of the electrolyte and adding the functional additive to the electrolyte of the sodium-ion battery, the cycle performance and rate performance of the sodium-ion battery were improved to a certain extent.

[0094] As can be seen from the comparison between Example 7 and Comparative Example 3 in Table 1, after changing the organic solvent component of the electrolyte and adding the functional additive to the electrolyte of the sodium-ion battery, the cycle performance and rate performance of the sodium-ion battery were improved to a certain extent.

[0095] As can be seen from the comparison between Example 8 and Comparative Example 4 in Table 1, after changing the positive electrode active material components and adding the functional additive to the electrolyte of the sodium-ion battery, the cycle performance and rate performance of the sodium-ion battery were improved to a certain extent.

[0096] Figure 1 This is a comparison graph showing the cycle performance of sodium-ion batteries in Example 1 and Comparative Example 1; by Figure 1 It can be seen that even with the addition of a small amount of additive, the cycle performance was significantly improved (13.6% improvement in Example 1). Figure 2 This is a comparison graph showing the cycle performance of sodium-ion batteries in Example 3 and Comparative Example 1; Figure 2 It can be seen that when the content of the functional additive falls within the preferred range, the capacity decays very little, and the performance improvement is relatively more significant. Thermogravimetric analysis of the cycled samples revealed that the interstitial water and lattice water contents of Examples 1 and 3 at 100–170°C and 200–270°C, respectively, decreased to varying degrees. Infrared spectroscopy results also showed that Examples 1 and 3 exhibited reductions in interstitial water and lattice water contents at a wavelength of 1625 cm⁻¹. -1 and 3436cm -1The corresponding water content also decreases. The above proof shows that the cations in the functional additive have a repulsive effect on water, only allowing the insertion and extraction of naked sodium ions, reducing the water content in the lattice, and further maintaining the framework stability during subsequent cycles.

[0097] Figure 3 It is a comparison chart of the rate performance of the sodium-ion batteries in Example 1 and Comparative Example 1; Figure 3 It can be seen that even with a small amount of additive added, its rate performance has a small increase. Figure 4 It is a comparison chart of the rate performance of the sodium-ion batteries in Example 3 and Comparative Example 1; Figure 4 It can be seen that when the content of the functional additive falls within the preferred range, the rate increase is relatively more obvious (the rate in Example 3 increases by 35.91%). After XRD tests are carried out on the samples before and after cycling, it is known that the peaks can be well indexed after comparison with the standard card JCPDS No: 73-0687, and the peaks after cycling in Example 1 and Example 3 are higher and stronger, indicating that structural rearrangement occurs in the samples after adding the functional additive and the crystallinity is good.

[0098] Figure 5 , Figure 6 and Figure 7 are respectively the SEM characterization results of the electrodes after multiple cycles in Comparative Example 1, Example 1 and Example 3. It can be clearly found that under the action of the functional additive of the present invention, the electrode surface is more uniform and has fewer defects, significantly reducing the cracking of the electrode during the charge and discharge process.

[0099] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms of specific transformations without departing from the purpose of the present invention and the scope protected by the claims. All of these fall within the protection scope of the present invention.

Claims

1. Use of a sodium-ion battery functional additive, characterized in that, Functional additives are added to and dissolved in the electrolyte of a sodium-ion battery, wherein the sodium-ion battery uses Prussian blue-like materials as the positive electrode active material. The functional additive is at least one of barium perchlorate and barium hexafluorophosphate, and the content of the functional additive is 6% to 20% of the total mass of the electrolyte.

2. The application of the sodium-ion battery functional additive according to claim 1, characterized in that, The molecular formula of the Prussian blue type material is A x M A [M B (CN)6] (1-y) ·□ y ·nH2O; wherein A is an alkali metal or alkaline earth metal cation, M A , M B is a transition metal cation, □ is an M B (CN)6 hole, 0 < x < 2, 0 ≤ y < 1.

3. The application of the sodium-ion battery functional additive according to claim 1, characterized in that, The electrolyte includes a non-aqueous organic solvent and a sodium salt dissolved in the non-aqueous organic solvent.

4. The application of the sodium-ion battery functional additive according to claim 3, characterized in that, The non-aqueous organic solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, ethyl methanesulfonate, dimethyl sulfite, and diethyl sulfite.

5. The application of the sodium-ion battery functional additive according to claim 3, characterized in that, The sodium salt is selected from at least one of sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonate).

6. A sodium-ion battery, wherein the sodium-ion battery uses a Prussian blue-like material as the positive electrode active material; characterized in that, The electrolyte of the sodium-ion battery contains a functional additive, which is at least one of barium perchlorate and barium hexafluorophosphate, and the content of the functional additive is 6% to 20% of the total mass of the electrolyte.

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