Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention relates to a high-stability sodium ion battery electrolyte and a sodium ion total battery using the same. The high-stability sodium ion battery electrolyte comprises an organic solvent, sodium salt and an additive. The additive comprises the negative electrode side additive and the positive electrode side additive, the negative electrode side additive and the positive electrode side additive form the composite additive, and the positive electrode side additive can effectively inhibit oxygenolysis of the electrolyte on the surface of a high-voltage positive electrode on the positive electrode side; and the negative electrode side additive in the composite additive can effectively inhibit reductive decomposition of the positive electrode side additive and the solvent on the low-potential negative electrode side on the negative electrode side. And the negative electrode side additive is an additive with a special structure, and the annular structure of the negative electrode side additive comprises-SO3 and C = C functional groups. And the positive electrode side additive is an additive with a special structure, and the structure of the additive comprises at least two-C = N functional groups. After the electrolyte containing the composite additive is applied to the sodium ion total battery, the irreversible capacity loss of the battery can be obviously reduced, and the cycle life of the battery can be obviously prolonged.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically a sodium-ion battery electrolyte and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries possess advantages such as abundant sodium resources, low cost, and high cost-effectiveness, showing broad application prospects in low- and medium-speed electric vehicles and large-scale energy storage. However, they are limited by their relatively low energy density and power density. Therefore, it is necessary to design positive electrode materials with high operating voltage and high energy density, and negative electrode materials with low operating voltage and high energy density. However, electrolytes at high voltage positive electrodes (>4.0V vs. Na / Na) present challenges. + The surface is highly susceptible to oxidative decomposition and operates at low working voltages (<1.0V vs. Na / Na). + The surface is highly susceptible to reductive decomposition, and this redox decomposition consumes active Na. + This causes a rapid decay of the full battery capacity, resulting in low energy density and poor cycle life of the full battery. Summary of the Invention

[0003] To address the aforementioned issues, research revealed that by introducing a special structural functional additive as the positive electrode side functional additive, combined with the negative electrode side functional additive, a high-voltage resistant sodium-ion battery electrolyte was designed. This positive electrode side functional additive contains at least one -C≡N functional group at the end of each carbon chain. Provided that one of the -C≡N functional groups participates in the sodium-ion solvation structure (this modified solvation structure reduces the interaction between the solvent and Na₂O₃), a suitable solution can be developed. + The coordination number, the charge and discharge process under voltage drive, the components in the electrolyte are Na + Solvated structural form "additive-Na" + The solvent-anion shuttles between the positive and negative electrode surfaces, and the decrease in solvent coordination number makes it more effective at high voltages (>4.0V vs. Na / Na). + The frequency and probability of this phenomenon on the positive electrode surface decrease, thereby reducing the oxidative decomposition of the electrolyte solvent on the high-voltage positive electrode surface. Another type of electrolyte preferentially adsorbs onto the positive electrode surface, contacting the high-voltage positive electrode, and subsequently undergoes preferential oxidative decomposition, thus constructing a stable CEI rich in nitrides, which can effectively inhibit the oxidative decomposition of the electrolyte on the high-voltage positive electrode surface.

[0004] However, in early studies of this invention, the electrolyte scheme containing only the positive electrode functional additive was introduced into a full cell with Na3V2(PO4)2F3 as the positive electrode and hard carbon as the negative electrode. It was found that the reversible cycle capacity and cycle life of the full cell were significantly reduced. This is because the positive electrode functional additive undergoes a violent reduction reaction on the negative electrode side, consuming bulk Na. + This results in a significant reduction in the battery's reversible cycle capacity and cycle life.

[0005] To this end, the present invention further explores and provides one or more functional additives for the negative electrode side, thereby inventing a highly stable sodium-ion battery electrolyte and a sodium-ion full battery that are compatible with all batteries.

[0006] Specifically, the sodium-ion battery electrolyte of the present invention includes an organic solvent, a sodium salt, and an additive, wherein the additive is a composite additive, including a negative electrode side functional additive and a positive electrode side functional additive.

[0007] The negative electrode side functional additive includes one or more of the structural compounds shown in Formula 1a or Formula 1b; preferably, a structural compound shown in Formula 1c (propylene-1,3-sulfonyl lactone (PES)).

[0008]

[0009] In equation 1a, R is C 1-10 Straight-chain alkyl (preferably C) 1-6 Straight-chain alkyl, more preferably C 1-4 (linear alkyl), in formula 1b, the two R1s are each independently C 1-10 Alkyl (preferably C) 1-6 Alkyl, more preferably C 1-4 alkyl);

[0010] The positive electrode side functional additive includes one or more of the compounds with the structure shown in Formula 2; preferably, it is a compound with the structure shown in Formula 2a (butadienenitrile (SN));

[0011]

[0012] In Equation 2, R2 is C 1-10 Alkyl (preferably C) 1-6 Alkyl, more preferably C 1-4 alkyl).

[0013] The present invention has found that, after applying the above-mentioned additives, the reversible cycle capacity of the battery is significantly improved and the cycle life is significantly increased.

[0014] Preferably, the final mass percentage of the positive electrode side functional additive in the electrolyte is 0.5-10%, more preferably 1-5%, and more preferably 2-3%.

[0015] Preferably, the final mass percentage of the negative electrode side functional additive in the electrolyte is 0.5-10%, more preferably 1-5%, and more preferably 2-3%.

[0016] Preferably, the sodium salt is one or more selected from sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(fluorosulfonyl)imide; the concentration of the sodium salt in the electrolyte is 0.2-3 mol / L.-1 Preferably 0.5-1.5 mol L -1 More preferably 0.8-1 mol L -1 .

[0017] Preferably, the organic solvent comprises one or more of cyclic carbonates, chain carbonates, and dimethyl ethers; the cyclic carbonate is selected from one or two of ethylene carbonate and propylene carbonate; the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, and methyl propyl carbonate; and the dimethyl ether is selected from one or more of dimethyl ether (DME), diethylene glycol dimethyl ether (DEG), and tetraethylene glycol dimethyl ether (TEG).

[0018] Preferably, the volume ratio of the cyclic carbonate to the chain carbonate is 1:1.

[0019] Those skilled in the art can combine the above solutions to obtain preferred embodiments of the electrolyte of the present invention.

[0020] Furthermore, the present invention also provides a sodium-ion battery containing the electrolyte described above.

[0021] Preferably, the positive electrode material of the battery is a polyanionic compound, including sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), Na3V2(PO4)2O2F, Na3V2(PO4)3, Na4VMn(PO4)3, Na4FeMn(PO4)3, Na3TiMn(PO4)3, Na4MnCr(PO4)3, Na3Fe2(SO4)3, NaFePO4, Na2FeP2O7, Na4Fe3(PO4)2P2O7, Na4Fe x Mn y (PO4)2P2O7, Na3NiZr(PO4)3, Na2FePO4F, Na2FeSiO4, and manganese-rich composite phosphate cathode Na4M3(PO4)2P2O7 (M is a combination of ≥3 high-abundance elements, which can be a combination of Mn with two or more of Fe, Cr, V, etc., where M is dominated by Mn, the molar percentage of Mn in the high-abundance elements is x, and 50%≤x<100%, and the total molar percentage of the other elements is 3-x) are one or more of these.

[0022] The negative electrode material of the battery is a carbon-based material, including one or two of hard carbon and soft carbon; the separator is one or two of glass fiber membrane and Celgard membrane.

[0023] Preferably, the positive electrode material of the battery is Na3V2(PO4)2F3 or Na3V2(PO4)2O2F.

[0024] Preferably, the negative electrode material of the battery is a hard carbon material.

[0025] Preferably, the separator of the battery is a Celgard membrane.

[0026] Preferably, the polyanionic positive and negative electrodes of the battery are arranged sequentially in the electrolyte through a separator, and the electrolyte is used as a sodium-ion full battery electrolyte.

[0027] Preferably, the full battery voltage range for charging and discharging is 2-4.5V, preferably 2-4.3V, corresponding to a positive electrode potential ≥4.5V vs. Na / Na, respectively. + Negative electrode potential ≤ 0.1V vs. Na / Na + Both the positive and negative electrodes can operate stably under this potential, thus the whole cell can operate stably within the selected voltage range of the whole cell.

[0028] Based on the above technical solution, the electrolyte of the present invention has the following advantages:

[0029] The electrolyte of this invention comprises a composite additive consisting of positive-side and negative-side functional additives. During the formation stage, the positive-side functional additives preferentially oxidize and decompose to form a film on the positive-side surface such as Na3V2(PO4)2F3, effectively suppressing the electrolyte at high-voltage positive electrodes (>4.0V vs. Na / Na). + The oxidation / reduction decomposition of the surface of the positive electrode leads to the preferential reduction and film formation of the negative electrode functional additive on the negative electrode surface, effectively inhibiting the reduction and decomposition of the positive electrode functional additive. This allows the positive electrode functional additive to effectively exert its function on the positive electrode side. Simultaneously, the negative electrode functional additive also effectively inhibits the reduction and decomposition of the solvent on the negative electrode side. Because the oxidation / reduction decomposition of the solvent in the electrolyte and the reduction and decomposition of the positive electrode functional additive consume active sodium ions in the positive electrode material, irreversible capacity loss occurs in the full cell, resulting in a decrease in the reversible cycle capacity. Furthermore, the negative electrode-electrolyte-interface film formed by the reduction and decomposition of the solvent and positive electrode functional additive on the negative electrode side cannot effectively inhibit the continuous reduction and decomposition of the solvent and positive electrode functional additive on the negative electrode side. This leads to a continuous decrease in the reversible cycle capacity of the full cell, resulting in a low cycle life. The electrolyte obtained after adding the aforementioned composite additives exhibits reduced consumption of active sodium ions at the positive electrode due to decreased oxidation / reduction decomposition of the solvent and reduction decomposition of the functional additives on the positive electrode side. This translates to reduced irreversible capacity loss in the full-cell performance, resulting in improved reversible cycle capacity and a significantly longer cycle life. The cycle life is measured by the difference in capacity retention after 1000 cycles (under 1C testing conditions); an increase in capacity retention indicates an improved cycle life. Attached Figure Description

[0030] Figure 1 Linear sweep voltammetry (LSV) for $1 and $2 (0-3V vs. Na / Na) + ).

[0031] Figure 2 The charge-discharge curves of Na3V2(PO4)2F3|hard carbon full cell in the voltage range of 2 to 4.2V at 0.05C are as follows: a) First charge curve on the hard carbon side, b) First charge curve on the Na3V2(PO4)2F3 side, c) First charge-discharge curve of Na3V2(PO4)2F3|hard carbon full cell.

[0032] Figure 3 The composition of the anode (hard carbon)-electrolyte interface formed by #2 and *2-1 was characterized by cryogenic transmission electron microscopy (cryo-TEM): a) #2, b) *2-1.

[0033] Figure 4 The composition of the anode (hard carbon)-electrolyte interface formed by *2-2 and *2-3 was characterized by cryogenic transmission electron microscopy (cryo-TEM): a) *2-2, b) *2-3.

[0034] Figure 5 1C cycle performance of #2 and *2-1, *2-2, *2-3 (Na3V2(PO4)2F3|hard carbon system). Detailed Implementation

[0035] Ethylene carbonate / propylene carbonate (1 / 1, volume ratio) solvent system:

[0036] Example 1 (#1)

[0037] This embodiment prepares 0.5 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) and 2% succinate (SN) added by mass.

[0038] Example 2 (#2)

[0039] This embodiment prepares 0.8 mol L -1The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) and 2% succinate (SN) added by mass.

[0040] propylene carbonate / dimethyl carbonate (1 / 1, volume ratio) solvent system:

[0041] Example 3 (#3)

[0042] This embodiment prepares 0.5 mol L -1 The NaPF6 electrolyte is prepared by solvents of propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) and 2% succinate (SN) added by mass.

[0043] Example 4 (#4)

[0044] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) and 2% succinate (SN) added by mass.

[0045] Diethylene glycol dimethyl ether (DEG) solvent system:

[0046] Example 5 (#5)

[0047] This embodiment prepares 0.5 mol L -1 The NaPF6 electrolyte is prepared using diethylene glycol dimethyl ether (DEG) as the solvent, with 2% (final mass) of propylene-1,3-sulfonyl lactone (PES) and 2% (final mass) of succinate (SN).

[0048] Example 6 (#6)

[0049] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared using diethylene glycol dimethyl ether (DEG) as the solvent, with 2% (final mass) of propylene-1,3-sulfonyl lactone (PES) and 2% (final mass) of succinate (SN).

[0050] Different combinations of negative electrode-side functional additives and positive electrode-side functional additives:

[0051] Example 7 (#7)

[0052] This embodiment prepares 0.8 mol L -1The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 2% by final mass of 1,4-butene sulfonyl lactone (BTS) and 2% by final mass of succinate (SN).

[0053] Example 8 (#8)

[0054] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) and 2% heptanonitrile (DNP) added.

[0055] Example 9 (#9)

[0056] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 2% by final mass of 1,4-butene sulfonyl lactone (BTS) and 2% by final mass of heptanonitrile (DNP).

[0057] Ethylene carbonate / propylene carbonate (1 / 1, volume ratio) solvent system:

[0058] Comparative Example 1-1 (*1-1)

[0059] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte has the following solvent: ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio).

[0060] Comparative Examples 1-2 (*1-2)

[0061] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate and propylene carbonate in a 1 / 1 ratio (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) added as a final mass percentage.

[0062] Comparative Examples 1-3 (*1-3)

[0063] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte is prepared by using a solvent of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio) and adding 2% succinate (SN) by mass.

[0064] Comparative Example 2-1 (*2-1)

[0065] This comparative example prepared 0.8 mol L -1The NaPF6 electrolyte has the following solvent: ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio).

[0066] Comparative Example 2-2 (*2-2)

[0067] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate and propylene carbonate in a 1 / 1 ratio (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) added as a final mass percentage.

[0068] Comparative Example 2-3 (*2-3)

[0069] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by using a solvent of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio) and adding 2% succinate (SN) by mass.

[0070] propylene carbonate / dimethyl carbonate (1 / 1, volume ratio) solvent system:

[0071] Comparative Example 3-1 (*3-1)

[0072] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte has the following solvent: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio).

[0073] Comparative Example 3-2 (*3-2)

[0074] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte is prepared by solvents of propylene carbonate and dimethyl carbonate in a 1 / 1 ratio (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) added as a final mass percentage.

[0075] Comparative Example 3-3 (*3-3)

[0076] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte is prepared by using a solvent of propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio) and adding 2% succinate (SN) by mass.

[0077] Comparative Example 4-1 (*4-1)

[0078] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte has the following solvent: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio).

[0079] Comparative Example 4-2 (*4-2)

[0080] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of propylene carbonate and dimethyl carbonate in a 1 / 1 ratio (volume ratio), with 2% propylene-1,3-sulfonyl lactone (PES) added as a final mass percentage.

[0081] Comparative Example 4-3 (*4-3)

[0082] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by using a solvent of propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio) and adding 2% succinate (SN) by mass.

[0083] Diethylene glycol dimethyl ether (DEG) solvent system:

[0084] Comparative Example 5-1 (*5-1)

[0085] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte uses diethylene glycol dimethyl ether (DEG) as the solvent.

[0086] Comparative Example 5-2 (*5-2)

[0087] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte is prepared using diethylene glycol dimethyl ether (DEG) as the solvent, with 2% (by weight) of propylene-1,3-sulfonyl lactone (PES).

[0088] Comparative Example 5-3 (*5-3)

[0089] This comparative example prepares 0.5 mol L... -1 The NaPF6 electrolyte is prepared using diethylene glycol dimethyl ether (DEG) as the solvent, with 2% succinate (SN) added as the final mass percentage.

[0090] Comparative Example 6-1 (*6-1)

[0091] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte uses diethylene glycol dimethyl ether (DEG) as the solvent.

[0092] Comparative Example 6-2 (*6-2)

[0093] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared using diethylene glycol dimethyl ether (DEG) as the solvent, with 2% (by weight) of propylene-1,3-sulfonyl lactone (PES).

[0094] Comparative Example 6-3 (*6-3)

[0095] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared using diethylene glycol dimethyl ether (DEG) as the solvent, with 2% succinate (SN) added as the final mass percentage.

[0096] Different combinations of negative electrode-side functional additives and positive electrode-side functional additives:

[0097] Comparative Example 7-1 (*7-1)

[0098] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate and propylene carbonate in a 1 / 1 ratio (volume ratio), with 2% 1,4-butene sulfonyl lactone (BTS) added as a final mass percentage.

[0099] Comparative Example 8-1 (*8-1)

[0100] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by using a solvent of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio) and adding 2% heptanonitrile (DNP) by mass.

[0101] Experimental Example

[0102] Experimental Example 1 ($1)

[0103] This comparative example prepared 0.8 mol L -1 NaPF6 electrolyte, with succinate (SN) as the solvent.

[0104] Experimental Example 2 ($2)

[0105] This comparative example prepared 0.8 mol L -1 The NaPF6 electrolyte is prepared by a solvent of succinate (SN) / propenyl-1,3-sulfonyl lactone (PES) = 1 / 1 (volume ratio).

[0106] Detailed experimental procedure:

[0107] Linear Scan Voltammetry (LSV) test

[0108] To demonstrate the severe reductive decomposition of the positive electrode functional additive at low potential, and the effect of the negative electrode functional additive in inhibiting the reductive decomposition of the positive electrode functional additive, electrolytes $1 and $2 were injected into an electrolytic cell (using a 10*10*0.1 mm Pt sheet as the working electrode, a 10*10*0.1 mm Cu sheet as the counter electrode, and a 10*10*0.1 mm Na metal sheet as the reference electrode). The reaction was carried out at 1 mV s. -1The scan rate is between 3 and 0V (vs. Na / Na). + Linear ScanVoltage (LSV) tests were performed within the voltage range to obtain... Figure 1 The results are shown.

[0109] Figure 1 This demonstrates the severe reductive decomposition of the positive electrode functional additive at low potentials, and the effect of the negative electrode functional additive in inhibiting the reductive decomposition of the positive electrode functional additive. Specifically, the LSV curve of $1 is shown below 1.0V (vs. Na / Na). + A significant reduction current appears at ~0.3V (vs. Na / Na). + The strong reduction current peak at this point indicates that the functional additives (such as SN) on the positive electrode side can achieve reduction currents below 1.0V (vs. Na / Na). + The reduction on the negative electrode side is severe. However, after adding the negative electrode functional additive (PES), the reduction potential of the negative electrode functional additive in the LSV curve of $2 is ~1.4V (vs. Na / Na). + The negative electrode functional additive preferentially undergoes reduction and decomposition compared to the positive electrode functional additive. At this time, the reduction current and peak value of the positive electrode functional additive are significantly reduced (the peak value of the reduction current is reduced by 1 / 39), indicating that the negative electrode functional additive inhibits the violent reduction and decomposition of the positive electrode functional additive at low potential.

[0110] Cryogenic transmission electronmicroscopy (cryo-TEM) test

[0111] Cells injected with electrolytes #2, *2-1, *2-2, and *2-3 (cell preparation is described in the "Battery Performance Testing" section) were formed in a 45°C forced-air drying oven at 0.05C within a voltage range of 2–4.3V. After the first charge cycle, the hard carbon anode of the cell was removed and rinsed ≥5 times with dimethyl carbonate solvent, then dried in a glove box at 45°C. The dried electrode was then subjected to Cryogenic Transmission Electron Microscopy (cryo-TEM) to obtain the interfacial film structure on the surface of the hard carbon anode, as shown below. Figure 3 and Figure 4 .

[0112] Figure 3 and Figure 4This study demonstrates that the functional additives (PES) on the negative electrode side construct a good negative electrode-electrolyte-interface film on the hard carbon negative electrode side. Among these, the interfacial film constructed by one of the electrolytes of this invention (#2) is the optimal and densest, rich in beneficial inorganic components such as NaF, Na2S, and Na2SO3. In contrast, the interfaces constructed by the comparative electrolytes *2-1, *2-2, and *2-3 are not dense and lack inorganic component richness. This indicates that the electrolyte of this invention constructs a good interfacial film on the hard carbon negative electrode side. This interfacial film inhibits the continuous decomposition of the electrolyte, thereby improving battery cycle life (reflected in the capacity retention rate of over 85% after 1000 cycles).

[0113] Battery performance test

[0114] The electrolytes used in the above examples and comparative examples (as electrolytes for sodium-ion full batteries, i.e., as electrolytes for both positive and negative electrodes) were injected into sodium-ion full battery pouch cells (the positive electrode active materials were Na3V2(PO4)2F3 or Na3V2(PO4)2O2F, respectively; the electrode components included electrode active materials, conductive agent carbon black, and binder PVDF, which were thoroughly mixed at a mass ratio of 94:3:3 and then coated onto aluminum foil). The cells were then placed in a vacuum oven at 90°C for 48 hours, resulting in a final loading of 11.0 mg / cm³ on the aluminum foil. -2 The electrode was cut into 106*76mm length-width sheets. The negative electrode active material was hard carbon, prepared using the same method as the positive electrode. The electrode composition included the active material, conductive agent carbon black, and binder PVDF, which were thoroughly mixed in a mass ratio of 94:3:3 and then coated onto aluminum foil. After being placed in a 90℃ vacuum oven for 48 hours, the final loading on the aluminum foil was 4.0 mg / cm³. -2 The electrode sheets are cut to a length and width of 108*78mm; the membrane is a Celgard membrane, and then assembled into a ~0.5Ah soft-pack battery cell.

[0115] To monitor the potential changes of the positive and negative electrodes during charging and discharging, after the pouch battery cells were assembled, a 20mm x 2mm x 1mm metallic Na electrode was placed 2mm away from the cell as a reference electrode, and the battery was then sealed. After injecting the electrolyte as described above, it was charged and discharged at 0.05C. Figure 2 As shown.

[0116] Figure 2 First of all Figure 2 The circled part in a (*2-3) shows the violent reduction and decomposition of the positive electrode functional additive (SN) at low potential of the hard carbon negative electrode. However, this position disappears when the negative electrode functional additive (PES) (#2) is added, which proves that the negative electrode functional additive inhibits the violent reduction and decomposition of the positive electrode functional additive at low potential of the hard carbon negative electrode. Figure 2In b, the charging curves of *2-3 and #2 both show the oxidation of the positive electrode functional additive (SN), proving that the positive electrode functional additive (SN) is oxidized and decomposed on the positive electrode side, thus exerting its positive electrode side function. Figure 2 c combination Figure 2 a and 2b are used to map the full cell voltage to the potentials of the hard carbon negative electrode and the Na3V2(PO4)2F3 positive electrode. In 2a and 2b, the voltage is relative to Na / Na. + The potential of the cathode is 2C, while the potential difference between the positive and negative electrodes is 2C. Within a voltage range of 2–4.2V, the negative electrode potential on the hard carbon side is as low as 0.1V (vs. Na / Na). + This is far lower than the reduction potential of the solvent and the functional additive on the positive electrode side, so it will undergo reduction decomposition on the negative electrode side, while the positive electrode potential of Na3V2(PO4)2F3 is as high as 4.4V (vs. Na / Na). + The potential of the positive electrode is much higher than that of the solvent, so the solvent will undergo oxidative decomposition on the positive electrode side.

[0117] The aforementioned battery cells were formed in a 45°C forced-air drying oven at 0.05C within a voltage range of 2–4.3V. Next, they were calibrated at room temperature at 0.2C within a voltage range of 2–4.3V to obtain the reversible cycle capacity. Finally, cycle performance was tested at room temperature at 1C within a voltage range of 2–4.3V, and the results are shown below. Figure 5 See Table 1.

[0118] Figure 5 The figure shows the capacity retention of Na3V2(PO4)2F3|hard carbon full cells under different cycle numbers. One of the electrolytes of this invention (#2) has a capacity retention of up to 86.67% after 1000 cycles, while the other comparative samples *2-1, *2-2, and *2-3 have a capacity retention of 65.35%, 76.96%, and 20%, respectively, all lower than that of #2. This indicates that the cycle life of Na3V2(PO4)2F3|hard carbon full cells using the electrolyte of this invention is significantly improved.

[0119] Table 1. Results of ambient temperature cycling tests for the examples and comparative examples.

[0120]

[0121] Based on the results, in the Linear ScanVoltammetry test ( Figure 1 ) and three-electrode soft-pack charge-discharge test ( Figure 2 In the results, after adding functional additives to both the positive and negative electrode sides, the solvent at the high-voltage positive electrode (>4.0V vs. Na / Na) showed... + Oxidative decomposition of the surface was significantly inhibited, and the functional additives and solvents on the positive electrode side were effective at low voltage negative electrode (>1.0V vs. Na / Na). +The reductive decomposition of the surface is suppressed. Battery performance data shows that the cycle life of full cells using this electrolyte is slightly improved, as evidenced by the capacity retention rate after 1000 cycles at 1C at room temperature increasing from ~65% for the blank sample without additives, ~75% for the control sample with only negative electrode functional additives, and ~20% for the control sample with only positive electrode functional additives to over 85%. Figure 5 (and Table 1). Simultaneously, batteries using the electrolyte of this invention exhibit reduced loss of active sodium ions in the positive electrode material due to suppressed solvent oxidation / reduction decomposition, resulting in reduced irreversible capacity loss and improved reversible cycle capacity (from ~85 mAh g in the blank sample without additives). -1 The control sample with only negative electrode-side functional additives added had a capacity of ~90 mAh g. -1 The comparison sample with only positive electrode functional additives added has a capacity of ~88 mAh g. -1 Increased to ~100mAh g -1 (Table 1).

[0122] Different additive content systems:

[0123] Example 10-1 (#10-1)

[0124] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by a solvent of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 0.5% propylene-1,3-sulfonyl lactone (PES) and 0.5% succinate (SN) added by mass.

[0125] Example 10-2 (#10-2)

[0126] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 1% propylene-1,3-sulfonyl lactone (PES) and 1% succinate (SN) added by mass.

[0127] Example 10-3 (#10-3)

[0128] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 3% propylene-1,3-sulfonyl lactone (PES) and 3% succinate (SN) added by mass.

[0129] Example 10-4 (#10-4)

[0130] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 5% propylene-1,3-sulfonyl lactone (PES) and 5% succinate (SN) added by mass.

[0131] Example 10-5 (#10-5)

[0132] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 10% propylene-1,3-sulfonyl lactone (PES) and 10% succinate (SN) added by mass.

[0133] Comparative Example 10⁻¹ (*10⁻¹)

[0134] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by a solvent of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with the addition of 0.1% propylene-1,3-sulfonyl lactone (PES) and 0.1% succinate (SN) by final mass percentage.

[0135] Comparative Example 10⁻² (*10⁻²)

[0136] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte is prepared by solvents of ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio), with 15% propylene-1,3-sulfonyl lactone (PES) and 15% succinate (SN) added by mass.

[0137] A cathode-side functional additive system containing only a single -C≡N functional group:

[0138] Comparative Example 11-1 (*11-1)

[0139] This embodiment prepares 0.8 mol L -1 The NaPF6 electrolyte has the following solvent: ethylene carbonate / propylene carbonate = 1 / 1 (volume ratio). 2% of propylene-1,3-sulfonyl lactone (PES) and 2% of acrylonitrile (ANN) are added, wherein the acrylonitrile contains only one -C≡N functional group.

[0140] Table 2. Results of ambient temperature cycling tests for the examples and comparative examples.

[0141]

[0142] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A sodium-ion battery electrolyte, comprising an organic solvent, a sodium salt, and additives, characterized in that: The additive is a composite additive, including a negative electrode side functional additive and a positive electrode side functional additive. The negative electrode side functional additive includes one or more of the compounds with the structures shown in Formula 1a or Formula 1b; In equation 1a, R is C 1-10 Straight-chain alkyl (preferably C) 1-6 Straight-chain alkyl, more preferably C 1-4 (linear alkyl), in formula 1b, the two R1s are each independently C 1-10 Alkyl (preferably C) 1-6 Alkyl, more preferably C 1-4 alkyl); The positive electrode side functional additives include one or more of the compounds with the structure shown in Formula 2; In Equation 2, R2 is C 1-10 Alkyl (preferably C) 1-6 Alkyl, more preferably C 1-4 alkyl).

2. The sodium-ion battery electrolyte according to claim 1, characterized in that: Organic solvents include one or more of cyclic carbonates, chain carbonates, and dimethyl ethers; The cyclic carbonate is selected from one or both of ethylene carbonate and propylene carbonate; The chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, and methyl propyl carbonate. The dimethyl ether is selected from one or more of dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

3. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that: The sodium salt is one or more selected from sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(fluorosulfonyl)imide; the concentration of the sodium salt in the electrolyte is 0.2-3 mol / L. -1 Preferably 0.5-1.5 mol / L -1 More preferably 0.8-1.0 mol L -1 .

4. The sodium-ion battery electrolyte according to claim 1, characterized in that: The final mass percentage of the negative electrode side functional additive in the electrolyte is 0.5-10%, preferably 1-5%, and more preferably 2-3%.

5. The sodium-ion battery electrolyte according to claim 1, characterized in that: The final mass percentage of the positive electrode side functional additive in the electrolyte is 0.5-10%, preferably 1-5%, and more preferably 2-3%.

6. A sodium-ion battery, characterized in that: The electrolyte used is the electrolyte according to any one of claims 1-5.

7. The battery according to claim 6, characterized in that: The positive electrode active material of the sodium-ion battery is a polyanionic compound, including Na3V2(PO4)2F3, Na3V2(PO4)2O2F, Na3V2(PO4)3, Na4VMn(PO4)3, Na4FeMn(PO4)3, Na3TiMn(PO4)3, Na4MnCr(PO4)3, Na3Fe2(SO4)3, NaFePO4, Na2FeP2O7, Na4Fe3(PO4)2P2O7, and Na4Fe x Mn y (PO4)2P2O7, Na3NiZr(PO4)3, Na2FePO4F, Na2FeSiO4, and manganese-rich composite phosphate cathode Na4M3(PO4)2P2O7 (M is a combination of ≥3 high-abundance elements, which can be a combination of Mn with two or more of Fe, Cr, V, etc., where M is dominated by Mn, the molar percentage of Mn in the high-abundance elements is x, and 50%≤x<100%, and the total molar percentage of the other elements is 3-x) are one or more of these.

8. The battery according to claim 7, characterized in that: The negative electrode material of the sodium-ion battery is a carbon-based material, including one or two of hard carbon and soft carbon; the separator is one or two of glass fiber membrane and Celgard membrane, with Celgard membrane being preferred.

9. The battery according to claim 6, 7, or 8, characterized in that: The polyanionic positive and negative electrodes of the sodium-ion battery are arranged sequentially in the electrolyte through a membrane, and the electrolyte of any one of claims 1-5 is used as the electrolyte of a sodium-ion full battery.

10. The battery according to claim 9, characterized in that: The full-cell voltage range for charging and discharging is 2-4.5V, preferably 2-4.3V, corresponding to a positive electrode potential ≥4.5V vs. Na / Na, respectively. + Negative electrode potential ≤ 0.1V vs. Na / Na + Both the positive and negative electrodes can operate stably under this potential, thus the whole cell can operate stably within the selected voltage range of the whole cell.

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