Sodium-ion battery

Abstract

Provided is a sodium-ion battery, comprising an electrolyte solution, a positive electrode sheet, a negative electrode sheet and a separator. The components of the electrolyte solution include an electrolyte salt, an organic solvent and a combined additive, wherein the combined additive comprises an additive A and an additive B, the additive A being a compound represented by formula I, and the additive B being a compound represented by formula II. Further provided are a preparation method for the electrolyte solution and a sodium-ion battery containing the electrolyte solution.

Description

A sodium-ion battery Technical Field

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

[0002] Lithium-ion batteries, currently the best-performing rechargeable batteries overall, boast high energy density, excellent performance, good safety, and low cost, leading to their widespread application in digital devices, automobiles, and energy storage. In lithium-ion batteries, both the positive electrode active material and the lithium salt in the electrolyte are made from lithium-containing compounds. The positive electrode material accounts for approximately 40% of the total cost of a lithium-ion battery, while the lithium salt accounts for approximately 50%. Therefore, the price of lithium ore has a significant impact on the price of lithium-ion batteries. China's lithium resources are extremely scarce, relying heavily on imports. Sodium, one of the most abundant elements in nature, is widely distributed and is also one of the best elements for battery manufacturing. Against this backdrop, researchers invented the sodium-ion battery.

[0003] Sodium-ion batteries typically use layered oxides such as Prussian blue and Prussian white for the positive electrode, and hard carbon for the negative electrode. The main drawback of sodium-ion batteries is their relatively low energy density, but they offer excellent safety performance and are cheaper than lithium iron phosphate batteries. They also have lower requirements for electrolyte concentration, as sodium (Na) does not form alloys with al (Al), allowing al to be used as the current collector in the negative electrode. Over-discharge is risk-free, resulting in high safety, making them ideal for energy storage systems and applications where volumetric energy density requirements are not high, such as two-wheeled vehicles.

[0004] However, the stability of the solid electrolyte interface (SEI) in sodium-ion batteries is worse than that in lithium-ion batteries, and they are prone to gas generation during cycling, resulting in poor cycle performance. Therefore, there is an urgent need to develop a sodium-ion battery that balances cycle performance and other key performance characteristics.

[0005] Summary of the Invention

[0006] This application aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, this application provides a sodium-ion battery that balances cycle performance and other key performance characteristics.

[0007] This application also provides a method for preparing a sodium-ion battery electrolyte.

[0008] This application provides a sodium-ion battery, including an electrolyte, a positive electrode, a negative electrode, and a separator. The electrolyte comprises an electrolyte salt, an organic solvent, and a combination of additives. The combination of additives includes additive A and additive B. Additive A is a compound represented by Formula I, and additive B is a compound represented by Formula II.

[0009] The compound represented by Formula I has the following structure:

[0010] The compound represented by Formula II has the following structure:

[0011] In Formula II, R1-R5 are each independently selected from hydrogen atoms, C1-C 10 Alkyl, C1-C 10 Fluoroalkyl, C2-C 10 alkenyl, C2-C 10 Fluoroalkenyl, C2-C 10 alkynyl group, C2-C 10 Fluoro-alkynyl, C6-C 10 aromatic groups and C6-C 10 One of the halogenated aromatic groups; and / or, R1-R5 are each independently selected from one of the following halogenated alkyl, phenyl, biphenyl, naphthyl, pyridyl, thiophenyl, halophenyl, halobiphenyl, phenolyl, alkyl-containing phenolyl, alkenyl-containing phenolyl, acetylinyl-containing phenolyl, nitrile-containing phenolyl, monohalogenated phenolyl, and polyhalogenated phenolyl;

[0012] The N / P ratio of the sodium-ion battery is x; the positive electrode sheet includes a positive electrode active material, and the compaction density of the positive electrode active material is w g / cm³. 3 The additive A in the electrolyte has a mass percentage content of y%, and the additive B in the electrolyte has a mass percentage content of z%. The following relationship must be satisfied between w, x, y, and z: 0.2 ≤ (wx) 2 ) / min[(y+z),(y / z)]≤5.

[0013] One of the technical solutions in this application regarding sodium-ion batteries has at least the following beneficial effects:

[0014] This application uses additive A as an auxiliary solvent and film-forming additive, which optimizes the solvation structure, enhances the stability of the SEI, reduces its dissolution during cycling, and simultaneously reduces Na in the SEI film. x PO y F z Increasing the content of NaF can improve the stability of the SEI and inhibit its dissolution. Among the SEI components of sodium-ion batteries, NaF has the highest LUMO energy level, weak electron affinity, low electron driving force of the SEI, and a large band gap, which is beneficial for enhancing the insulation capacity of the SEI and reducing its continuous growth.

[0015] This application introduces additive B as a film-forming additive based on additive A. B contains B atoms with empty orbitals, belonging to electron-deficient groups. It can form a complex with additive A, and then with PF6. - The formation of stable ionic complexes facilitates the dissociation of sodium salts and can also increase PF6. - This improves the stability of sodium salts, reduces their decomposition during cycling, and extends the cycle life of sodium-ion batteries.

[0016] Meanwhile, additives A and B work synergistically, maintaining a certain parameter relationship with the N / P ratio and cathode compaction density of the sodium-ion battery. Their combined effect suppresses sodium salt consumption, improves SEI stability, reduces electrolyte consumption during cycling, and improves cycle performance.

[0017] Compared with the prior art, this application has the following significant advantages:

[0018] Additive A has one more F atom than the commonly used additive fluoroethylene carbonate (FEC), resulting in a lower least occupied molecular orbital (LUMO) energy. This makes it easier to reduce than FEC, thus preferentially forming a film at the negative electrode. It also allows the SEI film to contain more NaF, thereby improving its stability. Furthermore, additive B, containing boron atoms with empty orbitals (an electron-deficient group), forms a complex with additive A, which in turn reacts with PF6. - The formation of stable ionic complexes facilitates the dissociation of sodium salts and can also increase PF6. - This improves the stability of sodium salts, reduces their decomposition during cycling, and extends the cycle life of sodium-ion batteries.

[0019] The sodium-ion battery of this application can significantly improve the performance of sodium nickel iron manganese oxide (Na[Ni)). 1 / 3 Fe 1 / 3 Mn 1 / 3 The stability of O2 and negative electrode hard carbon is improved, the dissolution of transition metal ions is inhibited, and the stability of SEI on the hard carbon surface is enhanced. This also inhibits the reaction of active end groups on the hard carbon surface, reduces electrolyte solvent loss and Na2O losses caused by active sites. + This reduces losses and improves the battery's ambient / high temperature cycle performance, high temperature storage performance, and thermal box performance.

[0020] In summary, this application improves the stability of the SEI by introducing additive A as an auxiliary solvent and film-forming additive, reducing the SEI's fragility and easy decomposition caused by the high concentration of low-lattice-energy compounds in the SEI component, and thus improving cycle performance. Introducing additive B as a film-forming additive enhances the stability of the sodium salt and participates in film formation, thereby improving SEI stability and cycle performance of the sodium-ion battery.

[0021] Additives A and B work synergistically to inhibit the damage of the positive electrode active material to the electrolyte, reduce electrolyte consumption during the cycle, and improve cycle performance.

[0022] This application introduces difluoroethylene carbonate as an auxiliary solvent and film-forming additive, and pyridine borate pinacol ester derivatives as film-forming additives. The content percentage of the two additives is defined in relation to the N / P ratio of the battery and the cathode compaction density. Through synergistic effect, the stability of the SEI of sodium-ion batteries is improved.

[0023] According to some embodiments of this application, the additive B is at least one having a structure of B1 to B3, wherein:

[0024] The structure of B1 is as follows:

[0025] The structure of B2 is:

[0026] The structure of B3 is as follows:

[0027] According to some embodiments of this application, the amount of additive A added to the electrolyte is from 0.2 wt% to 15 wt%.

[0028] According to some embodiments of this application, the amount of additive A added to the electrolyte is 1 wt% to 8 wt%.

[0029] According to some embodiments of this application, the amount of additive B added to the electrolyte is from 0.1 wt% to 5 wt%.

[0030] According to some embodiments of this application, the amount of additive B added to the electrolyte is from 0.15 wt% to 2.5 wt%.

[0031] According to some embodiments of this application, the electrolyte also includes a solvent.

[0032] According to some embodiments of this application, the solvent is a mixture of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0033] According to some embodiments of this application, the electrolyte also includes sodium salts.

[0034] According to some embodiments of this application, the sodium salt includes at least one of sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0035] According to some embodiments of this application, the amount of sodium salt added to the electrolyte is 8 wt% to 20 wt%.

[0036] According to some embodiments of this application, the electrolyte also contains additives.

[0037] According to some embodiments of this application, the additive includes one of fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone, tris(trimethylsilane)borate (TMSB), and tris(trimethylsilane)phosphate (TMSP).

[0038] According to some embodiments of this application, the amount of the additive added to the electrolyte is from 0.1 wt% to 20 wt%.

[0039] According to some embodiments of this application, the method for preparing the electrolyte includes the following steps: mixing the components of the electrolyte according to the specified ratio.

[0040] The preparation method of electrolyte does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are readily available, the production cost is low, and it is easy to carry out industrial production.

[0041] According to some embodiments of this application, the hard carbon of the negative electrode adapted for sodium-ion batteries is Na[Ni]. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0042] The sodium-ion battery of this application can significantly improve the performance of sodium nickel iron manganese oxide (Na[Ni)). 1 / 3 Fe 1 / 3 Mn 1 / 3 The stability of O2 and negative electrode hard carbon is improved, the dissolution of transition metal ions is inhibited, and the stability of SEI on the hard carbon surface is enhanced. This also inhibits the reaction of active end groups on the hard carbon surface, reduces electrolyte solvent loss and Na2O losses caused by active sites. + This reduces losses and improves the battery's ambient / high temperature cycle performance, high temperature storage performance, and thermal box performance.

[0043] The sodium-ion battery of this application, by using the electrolyte of this application, possesses at least all the beneficial effects of an electrolyte. Specifically:

[0044] The sodium-ion battery of this application optimizes the solvation structure and enhances the stability of the solid electrolyte interface (SEI) by employing additive A as an auxiliary solvent and film-forming additive. This helps reduce SEI dissolution during cycling and improves SEI stability.

[0045] The sodium-ion battery of this application, by optimizing the electrolyte composition, can reduce the amount of Na in the SEI membrane. x PO yF z This increases the content of NaF, thereby improving the stability of SEI and inhibiting its dissolution.

[0046] The sodium-ion battery of this application improves battery performance because NaF has a high LUMO energy level and weak electron affinity, which helps to enhance the insulation capacity of the SEI and reduce the continuous growth of the SEI.

[0047] In the sodium-ion battery of this application, additive B, as a film-forming additive, contains B atoms and forms a complex with PF6. - It forms stable ionic complexes. This facilitates the dissociation of the sodium salt and increases PF6. - This improves the stability of sodium salts, reduces their decomposition during cycling, and extends the cycle life of sodium-ion batteries.

[0048] In the sodium-ion battery of this application, the synergistic effect of additives A and B helps to suppress sodium salt consumption, improve SEI stability, and reduce electrolyte consumption during cycling, thereby improving cycle performance.

[0049] According to some embodiments of this application, the N / P ratio of the sodium-ion battery is x, and the positive electrode compaction density is wg / cm³. 3 The mass percentage content of additive A is y%, and the mass percentage content of additive B is z%. The following relationship must be satisfied between w, x, y, and z: 0.5 ≤ (wx) 2 ) / min[(y+z),(y / z)]≤4.

[0050] In the above relationship, "min" refers to the smaller value between (y+z) and (y / z). For example, if y is 1 and z is 3, then y+z = 4, y / z = 1 / 3, and the value of / min[(y+z),(y / z)] is 1 / 3. Or, if y is 3 and z is 1, then y+z = 4, y / z = 3, and the value of / min[(y+z),(y / z)] is 3.

[0051] According to some embodiments of this application, the value of w ranges from 2.8 g / cm³. 3 Up to 3.2 g / cm 3 .

[0052] According to some embodiments of this application, the value of x ranges from 1.038 to 1.048.

[0053] According to some embodiments of this application, the value of y ranges from 0.2% to 15%.

[0054] According to some embodiments of this application, the value of z ranges from 0.1% to 5%.

[0055] According to some embodiments of this application, the sodium-ion battery further includes a cathode electrode, an anode electrode, and a separator.

[0056] According to some embodiments of this application, the cathode electrode includes an aluminum foil current collector and a cathode diaphragm.

[0057] According to some embodiments of this application, the cathode diaphragm includes a cathode active material (e.g., lithium nickel iron manganese oxide Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), conductive agents (e.g., Super-P), and binders (e.g., polyvinylidene fluoride (PVDF)).

[0058] According to some embodiments of this application, the anode electrode includes an aluminum foil current collector and an anode diaphragm.

[0059] According to some embodiments of this application, the anode membrane includes an anode active material (e.g., hard carbon), a conductive agent (e.g., carbon nanotubes (CNT)), a thickener (e.g., sodium carboxymethyl cellulose (CMC)), and a binder (e.g., polyacrylic acid (PAA) and / or styrene-butadiene rubber (SBR)). Detailed Implementation

[0060] The following are specific embodiments of this application, and the technical solutions of this application will be further described in conjunction with the embodiments, but this application is not limited to these embodiments.

[0061] In some embodiments of this application, a sodium-ion battery is provided, comprising an electrolyte, a positive electrode, a negative electrode, and a separator. The electrolyte comprises an electrolyte salt, an organic solvent, and a combination of additives, wherein the combination of additives comprises additive A and additive B; additive A is a compound represented by formula I, and additive B is a compound represented by formula II.

[0062] The compound represented by Formula I has the following structure:

[0063] The CAS number of the compound represented by Formula I is 311810-76-1.

[0064] The compound shown in Formula II has the following structure:

[0065] In Formula II, R1-R5 are each independently selected from hydrogen atoms, C1-C 10 Alkyl, C1-C 10 Fluoroalkyl, C2-C 10 alkenyl, C2-C 10 Fluoroalkenyl, C2-C 10 alkynyl group, C2-C10 Fluoro-alkynyl, C6-C 10 aromatic groups and C6-C 10 One of the halogenated aromatic groups; and / or, R1-R5 are each independently selected from one of the following halogenated alkyl, phenyl, biphenyl, naphthyl, pyridyl, thiophenyl, halophenyl, halobiphenyl, phenolyl, alkyl-containing phenolyl, alkenyl-containing phenolyl, acetylinyl-containing phenolyl, nitrile-containing phenolyl, monohalogenated phenolyl, and polyhalogenated phenolyl;

[0066] The N / P ratio of the sodium-ion battery is x; the positive electrode includes the positive electrode active material, and the compaction density of the positive electrode active material is w g / cm³. 3 The mass percentage content of additive A in the electrolyte is y%, and the mass percentage content of additive B in the electrolyte is z%. The following relationship must be satisfied between w, x, y, and z: 0.2 ≤ (wx) 2 ) / min[(y+z),(y / z)]≤5.

[0067] It is understood that the electrolyte of this application uses additive A as an auxiliary solvent and film-forming additive, which optimizes the solvation structure, enhances the stability of the SEI, reduces its dissolution during cycling, and simultaneously reduces Na in the SEI film. x PO y F z Increasing the content of NaF can improve the stability of the SEI and inhibit its dissolution. Among the SEI components of sodium-ion batteries, NaF has the highest LUMO energy level, weak electron affinity, low electron driving force of the SEI, and a large band gap, which is beneficial for enhancing the insulation capacity of the SEI and reducing its continuous growth.

[0068] It is also understood that in the electrolyte of this application, additive B is introduced as a film-forming additive. The structure of B contains B atoms, which have empty orbitals and belong to electron-deficient groups. It can form a complex with additive A, and then with PF6. - The formation of stable ionic complexes facilitates the dissociation of sodium salts and can also increase PF6. - This improves the stability of sodium salts, reduces their decomposition during cycling, and extends the cycle life of sodium-ion batteries.

[0069] In the electrolyte of this application, additives A and B work synergistically to inhibit sodium salt consumption, improve SEI stability, reduce electrolyte consumption during the cycling process, and improve cycling performance.

[0070] Specifically, compared with the prior art, this application has the following significant advantages:

[0071] Additive A has one more F atom than the commonly used additive FEC, resulting in a lower LUMO energy and easier reduction compared to FEC. Therefore, it preferentially forms a film at the negative electrode and allows the SEI film to contain more NaF, thus improving its stability. Simultaneously, additive B is introduced. B contains boron atoms with empty orbitals, making it an electron-deficient group. It can form a complex with additive A, and then with PF6... - The formation of stable ionic complexes facilitates the dissociation of sodium salts and can also increase PF6. - This improves the stability of sodium salts, reduces their decomposition during cycling, and extends the cycle life of sodium-ion batteries.

[0072] The sodium-ion battery of this application can significantly improve the performance of sodium nickel iron manganese oxide (Na[Ni)). 1 / 3 Fe 1 / 3 Mn 1 / 3 The stability of O2 and negative electrode hard carbon is improved, the dissolution of transition metal ions is inhibited, and the stability of SEI on the hard carbon surface is enhanced. This also inhibits the reaction of active end groups on the hard carbon surface, reduces electrolyte solvent loss and Na2O losses caused by active sites. + This reduces losses and improves the battery's ambient / high temperature cycle performance, high temperature storage performance, and thermal box performance.

[0073] In summary, this application improves the stability of the SEI by introducing additive A as an auxiliary solvent and film-forming additive, reducing the SEI's fragility and easy decomposition caused by the high concentration of low-lattice-energy compounds in the SEI component, and thus improving cycle performance. Introducing additive B as a film-forming additive enhances the stability of the sodium salt and participates in film formation, thereby improving SEI stability and cycle performance of the sodium-ion battery.

[0074] Additives A and B work synergistically to inhibit the damage of the positive electrode active material to the electrolyte, reduce electrolyte consumption during the cycle, and improve cycle performance.

[0075] In some embodiments of this application, additive B is at least one having a structure of B1 to B3, wherein:

[0076] The structure of B1 is as follows:

[0077] The CAS number for B1 is 754214-56-7.

[0078] The structure of B2 is:

[0079] The CAS number for B2 is 181219-01-2.

[0080] The structure of B3 is as follows:

[0081] The CAS number for B3 is 844891-01-6.

[0082] In some embodiments of this application, the amount of additive A added to the electrolyte is from 0.2 wt% to 15 wt%.

[0083] In some embodiments of this application, the amount of additive A added to the electrolyte is from 1 wt% to 8 wt%.

[0084] In some embodiments of this application, the amount of additive B added to the electrolyte is from 0.1 wt% to 5 wt%.

[0085] In some embodiments of this application, the amount of additive B added to the electrolyte is from 0.15 wt% to 2.5 wt%.

[0086] In some embodiments of this application, the electrolyte also includes a solvent.

[0087] In some embodiments of this application, the solvent is a mixture of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0088] In some embodiments of this application, the electrolyte composition further includes sodium salts. In some embodiments of this application, the sodium salts include at least one selected from sodium hexafluorophosphate (NaPF6), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), and sodium bis(fluorosulfonyl)imide (NaFSI).

[0089] In some embodiments of this application, the amount of sodium salt added to the electrolyte is from 8 wt% to 20 wt%.

[0090] In some embodiments of this application, the electrolyte components also include additives.

[0091] In some embodiments of this application, the additives include one of fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone, tris(trimethylsilane)borate (TMSB), and tris(trimethylsilane)phosphate (TMSP).

[0092] In some embodiments of this application, the amount of additive added to the electrolyte is from 0.1 wt% to 20 wt%.

[0093] In some embodiments of this application, the method for preparing the electrolyte includes the following steps: mixing the components of the electrolyte according to the specified ratio.

[0094] It is understood that the preparation method of this application does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are readily available, the production cost is low, and it is easy to industrialize.

[0095] In some embodiments of this application, the hard carbon of the negative electrode adapted for sodium-ion batteries is Na[Ni] 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0096] The sodium-ion battery of this application can significantly improve the performance of sodium nickel iron manganese oxide (Na[Ni)). 1 / 3 Fe 1 / 3 Mn 1 / 3 The stability of O2 and negative electrode hard carbon is improved, the dissolution of transition metal ions is inhibited, and the stability of SEI on the hard carbon surface is enhanced. This also inhibits the reaction of active end groups on the hard carbon surface, reduces electrolyte solvent loss and Na2O losses caused by active sites. + This reduces losses and improves the battery's ambient / high temperature cycle performance, high temperature storage performance, and thermal box performance.

[0097] It is understood that the sodium-ion battery of this application, by using the electrolyte of this application, possesses at least all the beneficial effects of an electrolyte. Specifically:

[0098] The sodium-ion battery of this application optimizes the solvation structure and enhances the stability of the solid electrolyte interface (SEI) by employing additive A as an auxiliary solvent and film-forming additive. This helps reduce SEI dissolution during cycling and improves SEI stability.

[0099] The sodium-ion battery of this application, by optimizing the electrolyte composition, can reduce the amount of Na in the SEI membrane. x PO y F z This increases the content of NaF, thereby improving the stability of SEI and inhibiting its dissolution.

[0100] The sodium-ion battery of this application improves battery performance because NaF has a high LUMO energy level and weak electron affinity, which helps to enhance the insulation capacity of the SEI and reduce the continuous growth of the SEI.

[0101] In the sodium-ion battery of this application, additive B, as a film-forming additive, contains B atoms and forms a complex with PF6. - It forms stable ionic complexes. This facilitates the dissociation of the sodium salt and increases PF6. - This improves the stability of sodium salts, reduces their decomposition during cycling, and extends the cycle life of sodium-ion batteries.

[0102] In the sodium-ion battery of this application, the synergistic effect of additives A and B helps to suppress sodium salt consumption, improve SEI stability, and reduce electrolyte consumption during cycling, thereby improving cycle performance.

[0103] In some embodiments of this application, the N / P ratio of the sodium-ion battery is x, and the positive electrode compaction density is wg / cm³. 3 The mass percentage content of additive A is y%, and the mass percentage content of additive B is z%. The following relationship must be satisfied between w, x, y, and z: 0.2 ≤ (wx) 2 ) / min[(y+z),(y / z)]≤5.

[0104] In the above relationship, "min" refers to the smaller value between (y+z) and (y / z). For example, if y is 1 and z is 3, then y+z = 4, y / z = 1 / 3, and the value of / min[(y+z),(y / z)] is 1 / 3. Or, if y is 3 and z is 1, then y+z = 4, y / z = 3, and the value of / min[(y+z),(y / z)] is 3.

[0105] In some embodiments of this application, the value of w ranges from 2.8 g / cm³. 3 Up to 3.2 g / cm 3 .

[0106] In some embodiments of this application, the value of x ranges from 1.038 to 1.048.

[0107] In some embodiments of this application, the value of y ranges from 0.2% to 15%.

[0108] In some embodiments of this application, the value of z ranges from 0.1% to 5%.

[0109] In some embodiments of this application, the sodium-ion battery further includes a cathode electrode, an anode electrode, and a separator.

[0110] In some embodiments of this application, the cathode electrode includes an aluminum foil current collector and a cathode diaphragm.

[0111] In some embodiments of this application, the cathode diaphragm includes a cathode active material (e.g., lithium nickel iron manganese oxide Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), conductive agents (e.g., Super-P), and binders (e.g., polyvinylidene fluoride (PVDF)).

[0112] In some embodiments of this application, the anode electrode includes an aluminum foil current collector and an anode diaphragm.

[0113] In some embodiments of this application, the anode membrane includes an anode active material (e.g., hard carbon), a conductive agent (e.g., carbon nanotubes (CNT)), a thickener (e.g., sodium carboxymethyl cellulose (CMC)), and a binder (e.g., polyacrylic acid (PAA) and / or styrene-butadiene rubber (SBR)).

[0114] The technical solution of this application will be better understood below with reference to specific embodiments.

[0115] It should be noted that all reagents used in the examples are available from commercially available sources.

[0116] Example 1

[0117] This embodiment provides an electrolyte. The specific preparation method is as follows:

[0118] In an argon-filled glove box, EC, PC, DMC, and DEC were mixed in a mass ratio of EC:PC:DMC:DEC = 20:20:50:10. Then, sodium hexafluorophosphate (NaPF6) at 12 wt% of the total electrolyte weight was slowly added to the mixed solution. Finally, additive A at 1.5 wt% of the total electrolyte weight, B1 at 1.5 wt%, 1,3-propanesulfonate lactone (PS) at 4 wt%, and tris(trimethylsilane)borate (TMSB) at 1 wt% of the total electrolyte weight were added. After stirring evenly, the sodium-ion battery electrolyte of this embodiment was obtained.

[0119] Furthermore, a positive electrode sheet was prepared. The specific preparation method is as follows:

[0120] The cathode diaphragm includes the cathode active material lithium nickel iron manganese oxide (Na[Ni]). 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF). The active material NFM: conductive agent Super P: PVDF = 97%: 1.7%: 1.3% by weight were mixed, and then N-methylpyrrolidone (NMP) was added. The mixture was stirred until homogeneous to prepare the sodium-ion battery positive electrode slurry. The positive electrode slurry was coated onto a current collector aluminum foil, dried at 85°C, and then cold-pressed. After edge trimming, cutting, and slitting, it was dried under vacuum at 85°C for 4 hours. The tabs were then welded to obtain the sodium-ion battery positive electrode sheet.

[0121] Furthermore, a negative electrode sheet was prepared. The specific preparation method is as follows:

[0122] The anode film comprises hard carbon as the anode active material, carbon nanotubes (CNTs) as the conductive agent, sodium carboxymethyl cellulose (CMC) as the thickener, and styrene-butadiene rubber (SBR) as the binder. The materials are mixed in a weight ratio of hard carbon:CNT:CMC:SBR = 96%:1.3%:1.2%:1.5%, and then deionized water is added and mixed thoroughly to prepare the negative electrode slurry. The negative electrode slurry is coated onto an aluminum foil current collector, dried at 85°C, cold-pressed, then trimmed, cut, and slit. Finally, it is dried under vacuum at 85°C for 12 hours to obtain the sodium-ion battery negative electrode sheet.

[0123] Furthermore, a pouch cell was fabricated. The specific fabrication method is as follows:

[0124] The resulting positive electrode (mainly composed of Na[Ni)) 1 / 3 Fe 1 / 3 Mn 1 / 3 The sodium-ion soft-pack battery is prepared by stacking the O2 (Xiamen Tungsten New Energy), separator (Shenzhen Xingyuan), and negative electrode (active material hard carbon, Shenzhen BTR) in sequence, with the separator positioned between the positive and negative electrodes, and then winding it to obtain a bare cell. The bare cell is placed in an aluminum-plastic film outer packaging, and the electrolyte prepared above is injected into the dried battery. The battery is then encapsulated, left to stand, formed, shaped, and tested for capacity to complete the preparation of the sodium-ion soft-pack battery.

[0125] The sodium-ion battery has an N / P ratio of 1.044 and a positive electrode compaction density of 3.0 g / cm³. 3 .

[0126] Examples 2 to 7

[0127] Except for the different electrolyte composition (see Table 1 below), all other parameters and processes are the same as in Example 1.

[0128] Example 8

[0129] Except for the positive electrode, the compaction density is 2.9 g / cm³. 3 Apart from the above, all other parameters and processes are consistent with those in Example 1.

[0130] Example 9

[0131] Except for the N / P ratio of 1.040, all other parameters and processes are the same as in Example 1.

[0132] Comparative Examples 1 to 3

[0133] Except for the different electrolyte composition, the other parameters and processes are the same as in Example 1.

[0134] Comparative Example 4

[0135] Except for the positive electrode, whose compaction density is 2.6 g / cm³. 3 Apart from the above, all other parameters and processes are consistent with those in Example 1.

[0136] Comparative Example 5

[0137] Except for the N / P ratio of 1.02, all other parameters and processes are the same as in Example 1.

[0138] The specific proportions of each embodiment and comparative example are shown in Table 1.

[0139] Table 1

[0140] Performance testing

[0141] The batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were subjected to relevant performance tests.

[0142] Room temperature cycle performance test: In a 25℃ environment, the battery after capacity gradation is charged to 4.0V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C, and then discharged to 2.0V at a constant current of 0.5C. This cycle is repeated, and the capacity retention rate at the 700th cycle is calculated using the following formula:

[0143] 700-week cycle capacity retention (%) = (700-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0144] High-temperature cycle performance test: In a 45℃ environment, the battery after capacity gradation is charged to 4.0V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C, and then discharged to 2.0V at a constant current of 0.5C. This cycle is repeated, and the capacity retention rate at the 700th cycle is calculated using the following formula:

[0145] 700-week cycle capacity retention (%) = (700-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0146] 85℃ 24h High-Temperature Storage Test: The battery was placed at room temperature and charged and discharged once at 0.5C (4.0V-2.0V). The discharge capacity C0 before storage was recorded. Then, the battery was charged to 4.0V (100% SOC) under constant current and constant voltage. The thickness d1 of the battery before high-temperature storage was measured using a PPG battery thickness gauge (600g). The battery was then placed in an 85℃ constant temperature chamber for 24 hours. After storage, the battery was removed and the thermal thickness d2 after storage was measured. The battery thickness expansion rate after 24 hours of storage at 85℃ was calculated. After the battery cooled at room temperature for 24 hours, it was discharged again at 0.5C to 2.0V under constant current, and then charged to 4.0V under constant current and constant voltage at 0.5C. The discharge capacity C1 and charge capacity C2 after storage were recorded. The remaining capacity and recovery rate of the battery after 24 hours of storage at 85℃ were calculated using the following formulas:

[0147] Thickness expansion rate after storage at 85℃ for 24 hours = (d2-d1) / d1×100%;

[0148] The remaining capacity after storage at 85℃ for 24 hours is calculated as C1 / C0 × 100%.

[0149] Capacity recovery rate after storage at 85℃ for 24 hours = C2 / C0 × 100%.

[0150] The results of the above performance tests are shown in Table 2.

[0151] Thermal shock performance: Under 25℃ ambient conditions, discharge to 2.0V with a given current of 0.2C; rest for 5 minutes; charge to 4.0V with a charging current of 0.2C. When the cell voltage reaches 4.0V, switch to constant voltage charging at 4.0V until the charging current ≤ cutoff current 0.05C; after resting for 1 hour, place the cell in an oven. The oven temperature is increased to 135±2℃ at a rate of 5±2℃ / min and maintained for 60 minutes before stopping. The judgment criterion is that the cell does not catch fire or explode.

[0152] Table 2

[0153] As can be seen from the test results of Examples 1-7 and Comparative Examples 1-4 in Table 2, the introduction of additive A into the electrolyte system can effectively improve the cycle performance and high-temperature performance of sodium-ion batteries, and the effect is very significant.

[0154] Additive A, acting as both an auxiliary solvent and a film-forming additive, optimizes the solvation structure, enhances the stability of the SEI, reduces its dissolution during cycling, and simultaneously reduces Na+ in the SEI film. x PO y F z Increasing the NaF content improves the stability of the SEI and inhibits its dissolution. Among the SEI components of sodium-ion batteries, NaF has the highest LUMO energy level, weaker electron affinity, lower electron driving force of the SEI, and a larger band gap, which is beneficial for enhancing the insulation capacity of the SEI and reducing its continuous growth.

[0155] Simultaneously, additive B is introduced. B contains a B atom with empty orbitals, making it an electron-deficient group. It can form a complex with additive A, and then with PF6. - The formation of stable ionic complexes facilitates the dissociation of sodium salts and can also increase PF6. - The stability of the electrolyte is improved, reducing the decomposition of sodium salt during cycling and extending the cycle life of sodium-ion batteries. The synergistic effect of A and B inhibits sodium salt consumption, improves SEI stability, reduces electrolyte consumption during cycling, and enhances cycle performance.

[0156] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the protection of the present application.

Claims

1. A sodium-ion battery, characterized in that, It includes an electrolyte, a positive electrode, a negative electrode, and a separator. The electrolyte comprises an electrolyte salt, an organic solvent, and a combination of additives. The combination of additives includes additive A and additive B. Additive A is a compound represented by Formula I, and additive B is a compound represented by Formula II. The compound represented by Formula I has the following structure: The compound represented by Formula II has the following structure: In Formula II, R1-R5 are each independently selected from hydrogen atoms, C1-C 10 Alkyl, C1-C 10 Fluoroalkyl, C2-C 10 alkenyl, C2-C 10 Fluoroalkenyl, C2-C 10 alkynyl group, C2-C 10 Fluoro-alkynyl, C6-C 10 aromatic groups and C6-C 10 One of the halogenated aromatic groups; and / or, R1-R5 are each independently selected from one of the following halogenated alkyl, phenyl, biphenyl, naphthyl, pyridyl, thiophenyl, halophenyl, halobiphenyl, phenolyl, alkyl-containing phenolyl, alkenyl-containing phenolyl, acetylinyl-containing phenolyl, nitrile-containing phenolyl, monohalogenated phenolyl, and polyhalogenated phenolyl; The N / P ratio of the sodium-ion battery is x; the positive electrode sheet includes a positive electrode active material, and the compaction density of the positive electrode active material is w g / cm³. 3 The additive A in the electrolyte has a mass percentage content of y%, and the additive B in the electrolyte has a mass percentage content of z%, where w, x, y, and z satisfy the following relationship: 0.2 ≤ (wx) 2 ) / min[(y+z),(y / z)]≤5.

2. The sodium-ion battery according to claim 1, characterized in that, The compound represented by Formula II has at least one of the structures B1 to B3, wherein: The structure of B1 is as follows: The structure of B2 is: The structure of B3 is as follows:

3. The sodium-ion battery according to claim 1, characterized in that, The amount of additive A added to the electrolyte is from 0.2 wt% to 15 wt%.

4. The sodium-ion battery according to claim 1, characterized in that, The amount of additive B added to the electrolyte is from 0.1 wt% to 5 wt%.

5. The sodium-ion battery according to claim 1, characterized in that, The electrolyte also includes sodium salts.

6. The sodium-ion battery according to claim 5, characterized in that, The sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(fluorosulfonyl)imide.

7. The sodium-ion battery according to claim 5, characterized in that, The amount of sodium salt added to the electrolyte is from 8 wt% to 20 wt%.

8. The sodium-ion battery according to any one of claims 1 to 7, characterized in that, The value of w ranges from 2.8 g / cm³. 3 Up to 3.2 g / cm 3 ; and / or, the value of x ranges from 1.038 to 1.048; and / or, the value of y ranges from 0.2% to 15%; and / or, the value of z ranges from 0.1% to 5%.

9. The sodium-ion battery according to any one of claims 1 to 7, characterized in that, The preparation method of the electrolyte includes the following steps: mixing the components of the electrolyte according to the specified ratio.

10. The sodium-ion battery according to any one of claims 1 to 7, characterized in that, The sodium-ion battery is adapted to use Na[Ni] hard carbon as the negative electrode. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

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