A sodium-ion battery

Abstract

In order to overcome the technical problems of low initial efficiency and low cycle performance of the existing sodium-ion battery added with sodium-rich transition metal oxide supplementing sodium additive, the application provides a sodium-ion battery, which comprises a non-aqueous electrolyte, a positive electrode and a negative electrode, the non-aqueous electrolyte comprises an additive, the additive comprises a sodium salt type additive, the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprises a sodium supplementing additive and a positive electrode active material, and the sodium supplementing additive is a sodium-rich transition metal oxide; the negative electrode comprises a negative electrode active material, and the sodium-ion battery satisfies the following relationship: 0.3 <= a / (b+c) <= 1.5, and 5 <= a <= 10, 1 <= b <= 10, and 2 <= c <= 12; the sodium-ion battery provided by the application reduces the internal resistance of the battery and improves the initial efficiency and cycle performance of the battery.

Description

Technical Field

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

[0002] Sodium-ion batteries are similar in principle and structure to lithium-ion batteries. Compared with lithium batteries, sodium-ion batteries have more abundant resources, lower cost, less fluctuation, and offer potential for substitution due to their wide temperature range and high safety. With the continuous advancement of sodium-ion battery technology, they will occupy an important position in my country's energy system, especially in the field of energy storage, where they have broad growth potential. Therefore, developing high-performance, low-cost sodium-ion batteries is a decisive factor in their industrialization. Hard carbon, due to its stable structure, high conductivity, high sodium storage, and high capacity, has become one of the best-performing and most likely to be industrially applied anode materials for sodium-ion batteries. However, due to the numerous defects and large specific surface area of ​​hard carbon, the formation of its SEI film (solid electrolyte membrane) and the side reactions at the electrode interface are accompanied by more severe irreversible sodium ion loss, directly affecting the energy density and cycle life of sodium-ion batteries, especially for full sodium-ion batteries. To address these issues, researchers have used various sodium replenishment techniques to compensate for irreversible sodium ion loss and improve the initial efficiency of sodium-ion batteries. For example, the existing Chinese patent CN111293290A discloses a sodium-rich transition metal oxide composite sodium-supplementing positive electrode active material, in which the sodium-supplementing additive is a sodium-rich transition metal oxide with the chemical formula Na. x MO y Wherein, M is one or more of Ni, Co, Fe, Mn, Ru, Ir, Sn, Cr, Cu, Nb, and Mo. This material uses a mixture of two or more sodium-replenishing materials as a positive electrode additive, which can effectively compensate for the active sodium loss in sodium-ion batteries. However, sodium-rich metal oxides used as sodium-replenishing additives have characteristics such as poor conductivity, high impedance, high activity, and easy decomposition and gas generation, resulting in batteries with low initial efficiency and poor cycle performance. Therefore, it is of great significance to develop sodium-ion batteries that can improve upon the use of sodium-replenishing additives containing sodium-rich transition metal oxides. Summary of the Invention

[0003] In view of the technical problems of low initial efficiency and low cycle performance of existing sodium-ion batteries with sodium-rich transition metal oxides, this application provides a sodium-ion battery.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0005] On one hand, this application provides a sodium-ion battery, comprising a non-aqueous electrolyte, a positive electrode, and a negative electrode. The non-aqueous electrolyte includes additives, including sodium salt additives. The positive electrode includes a positive electrode active material layer, which includes a sodium-replenishing additive and a positive electrode active material. The sodium-replenishing additive is a sodium-rich transition metal oxide. The negative electrode includes a negative electrode active material.

[0006] The sodium-ion battery satisfies the following relationship:

[0007] 0.3≤a / (b+c)≤1.5, and 5≤a≤10, 1≤b≤10, 2≤c≤12;

[0008] Wherein, the total mass of the sodium supplement additive and the positive electrode active material is 100%, and a is the mass content of the sodium supplement additive, in %;

[0009] b represents the mass content of the sodium salt additive in the non-aqueous electrolyte, in %;

[0010] c represents the particle size of the negative electrode active material, in μm.

[0011] Preferably, the sodium-ion battery satisfies the following relationship: 0.5≤a / (b+c)≤1.2.

[0012] Preferably, the total mass of the sodium supplement additive and the positive electrode active material is 100%, and the mass content a of the sodium supplement additive is in the range of 5.5% to 9%.

[0013] Preferably, the sodium salt additive includes one or more of sodium difluorosulfonamide, sodium difluorooxalate borate, and sodium difluorophosphate;

[0014] The sodium salt additive has a mass content (b) in the non-aqueous electrolyte ranging from 2% to 6%.

[0015] Preferably, the particle size c of the negative electrode active material is in the range of 3 μm to 9 μm.

[0016] Preferably, the additive further includes 1,3-propanesulfonate lactone, wherein the mass content of 1,3-propanesulfonate lactone in the non-aqueous electrolyte is 0.5% to 2%.

[0017] Preferably, the mass content of the 1,3-propanesulfonic acid lactone in the non-aqueous electrolyte is 1% to 2%.

[0018] Preferably, the sodium-rich transition metal oxide comprises a compound shown in Formula 1.

[0019] Na x M y O z Formula 1,

[0020] Wherein, 0.2 < x / y < 9, 0 < y < 6, 2 ≤ z ≤ 9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr.

[0021] Preferably, the sodium-rich transition metal oxide includes one or more of Na5NbO5, Na3NbO4, Na4Nb2O7, Na5VO5, Na3VO4, and Na3TaO4.

[0022] Preferably, the non-aqueous electrolyte further includes electrolyte salts, auxiliary additives, and non-aqueous organic solvents.

[0023] The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, and sodium bis(trifluoromethanesulfonyl)imide.

[0024] Based on the mass of the electrolyte as 100%, the mass content of the electrolyte salt is 8% to 14%.

[0025] The auxiliary additives include at least one of 1,4-butanesulfonate lactone, acrylate lactone, vinyl sulfate, and fluorovinyl carbonate.

[0026] The electrolyte has a mass of 100%, and the auxiliary additives have a mass content of 2.5% to 10%.

[0027] The non-aqueous organic solvent includes at least one of carbonates having 3 to 5 carbon atoms, carboxylic acid esters having 2 to 6 carbon atoms, and ethers having 4 to 10 carbon atoms.

[0028] The positive electrode active material includes at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds;

[0029] The negative electrode active material layer includes a negative electrode active material, which includes one or more of carbon-based materials, silicon-based materials, and tin-based materials.

[0030] Beneficial effects:

[0031] The sodium-ion battery provided in this application has a total mass of 100% for the sodium-supplementing additive and the positive electrode active material, where 'a' represents the mass content of the sodium-supplementing additive. This additive has a synergistic effect with the sodium salt additive and the negative electrode active material. Furthermore, there is a certain relationship between the mass content 'a' of the sodium-supplementing additive and the mass content 'b' of the sodium salt additive added to the electrolyte, and the particle size 'c' of the negative electrode active material. When 'a', 'b', and 'c' satisfy the relationship 0.3 ≤ a / (b+c) ≤ 1.5, it can effectively improve the conductivity of the electrolyte and the diffusion and transport rate of ions in the negative electrode material while ensuring optimal conductivity of the positive electrode. This effectively reduces the overall internal resistance of the battery and improves its initial efficiency and cycle performance. In addition, the addition of the sodium salt additive to the electrolyte also participates in the formation of the positive and negative electrode interface film, effectively protecting the stability of the negative electrode during testing, thereby further improving cycle performance. Detailed Implementation

[0032] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] This application provides a sodium-ion battery, comprising a non-aqueous electrolyte, a positive electrode, and a negative electrode. The non-aqueous electrolyte includes additives, including sodium salt-type additives. The positive electrode includes a positive electrode active material layer, which includes a sodium-replenishing additive and a positive electrode active material. The sodium-replenishing additive is a sodium-rich transition metal oxide. The negative electrode includes a negative electrode active material.

[0034] The sodium-ion battery satisfies the following relationship:

[0035] 0.3≤a / (b+c)≤1.5, and 5≤a≤10, 1≤b≤10, 2≤c≤12;

[0036] Wherein, the total mass of the sodium supplement additive and the positive electrode active material is 100%, and a is the mass content of the sodium supplement additive, in %;

[0037] b represents the mass content of the sodium salt additive in the non-aqueous electrolyte, in %;

[0038] c represents the particle size of the negative electrode active material, in μm.

[0039] Adding sodium-rich transition metal oxides as sodium-supplementing additives to sodium-ion batteries has been found to result in batteries with poor conductivity, high impedance, high activity, and easy decomposition and gas generation. This leads to low initial efficiency and cycle performance. To address this issue, the inventors, through extensive research, discovered that the total mass of the sodium-supplementing additive and the positive electrode active material should be 100%, where 'a' represents the mass content of the sodium-supplementing additive. This additive exhibits a synergistic effect with the sodium salt-type additive and the negative electrode active material. Furthermore, there is a specific relationship between the mass content of the sodium-supplementing additive 'a', the mass content of the sodium salt-type additive added to the electrolyte 'b', and the particle size 'c' of the negative electrode active material. When 'a', 'b', and 'c' satisfy the relationship 0.3 ≤ a / (b+c) ≤ 1.5, the conductivity of the electrolyte and the diffusion and transport rate of ions in the negative electrode material can be effectively improved while ensuring optimal conductivity of the positive electrode. This effectively reduces the overall internal resistance of the battery, improving its initial efficiency and cycle performance. Additionally, the addition of sodium salt-type additives to the electrolyte also participates in the formation of the positive and negative electrode interface film, effectively protecting the stability of the negative electrode during testing, thereby further improving cycle performance.

[0040] In some preferred embodiments, the sodium-ion battery satisfies the following relationship: 0.5 ≤ a / (b+c) ≤ 1.2.

[0041] Sodium-ion batteries satisfy the relationship 0.5≤a / (b+c)≤1.2, exhibiting high conductivity at the positive electrode and a significant increase in electrolyte conductivity. This enhances the diffusion and transport rate of sodium ions in the negative electrode active material, effectively reducing the overall internal resistance of the battery and improving its initial efficiency and cycle performance. Furthermore, the addition of sodium salt additives to the electrolyte participates in negative electrode film formation, creating a more stable interfacial film at the electrode interface. This prevents residual byproducts from sodium additives from damaging the positive and negative electrodes, effectively protecting the stability of the negative electrode during testing and further improving cycle performance.

[0042] Specifically, the relationship a / (b+c) for sodium-ion batteries can be 0.3, 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.5, etc., as long as the value of a / (b+c) is between 0.3 and 1.5. Specifically, the mass content b of sodium salt additives in the non-aqueous electrolyte ranges from 1% to 10%. This improves the overall conductivity of the electrolyte and also participates in the formation of the interfacial film between the positive and negative electrodes, protecting them. This effectively solves the problems of poor conductivity of sodium additives and the damage to the positive and negative electrodes caused by residual byproducts, thus improving battery performance and cycle life. If the mass content b of sodium salt additives in the non-aqueous electrolyte is less than 1%, the effect on improving the electrolyte conductivity is not significant, and it cannot effectively participate in the formation of the interfacial film between the positive and negative electrodes. If b is greater than 10%, the mass content of sodium salt additives in the electrolyte is too high, resulting in a thicker interfacial film formed at the electrode interface, a reduced sodium ion transport rate, and an increased battery impedance. Specifically, the mass content b of the sodium salt additive in the electrolyte can be 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10%, etc., as long as b is within the range of 1% to 10%.

[0043] In some preferred embodiments, the mass content b of the sodium salt additive in the non-aqueous electrolyte ranges from 2% to 6%.

[0044] When the mass content of sodium salt additives added to the electrolyte is within the above-mentioned preferred range, it can improve the overall conductivity of the electrolyte and form an interface film of moderate thickness and stable structure at the positive and negative electrode interfaces. This effectively solves the problems of poor conductivity of sodium additives and the damage of residual by-products to the positive and negative electrodes, thus improving battery performance and cycle performance.

[0045] In some embodiments, the sodium salt additive includes one or more of sodium difluorosulfonamide (NaFSI), sodium difluorooxalate borate (NaODFB), and sodium difluorophosphate (NaPO2F2).

[0046] In some embodiments, the total mass of the sodium supplementation additive and the positive electrode active material is 100%, and the mass content a of the sodium supplementation additive ranges from 5% to 10%.

[0047] Because sodium-replenishing additives themselves have poor conductivity and leave byproducts after the reaction, when the mass content 'a' of the sodium-replenishing additive is greater than 10%, the overall performance of the cathode material deteriorates; when the mass content 'a' of the sodium-replenishing additive is less than 5%, it has no sodium-replenishing effect. In sodium-ion batteries, taking the total mass of the sodium-replenishing additive and the cathode active material as 100%, the mass content 'a' of the sodium-replenishing additive is between 5% and 10%. In this case, the sodium-replenishing additive can effectively replenish sodium while also improving the conductivity of the cathode and reducing byproduct residues after the reaction, thus improving the battery's initial efficiency and cycle performance. Specifically, 'a' can be 5%, 5.5%, 6%, 6.4%, 7.0%, 7.3%, 7.6%, 8.0%, 9%, 10%, etc., as long as the value of 'a' is within the range of 5% to 10%.

[0048] In some preferred embodiments, the total mass of the sodium supplementation additive and the positive electrode active material is 100%, and the mass content a of the sodium supplementation additive ranges from 5.5% to 9%.

[0049] Within the aforementioned preferred range, sodium-replenishing additives in sodium-ion batteries not only provide good sodium replenishment but also improve the conductivity of the positive electrode, thereby enhancing the battery's initial efficiency and cycle performance.

[0050] In some embodiments, the sodium-rich transition metal oxide comprises a compound of Formula 1.

[0051] Na x M y O z Formula 1,

[0052] Wherein, 0.2 < x / y < 9, 0 < y < 6, 2 ≤ z ≤ 9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr.

[0053] In some preferred embodiments, the sodium-rich transition metal oxide includes one or more of Na5NbO5, Na3NbO4, Na4Nb2O7, Na5VO5, Na3VO4, and Na3TaO4. It is understood that this application does not limit the types of sodium-rich transition metal oxides described above.

[0054] In some embodiments, the particle size c of the negative electrode active material ranges from 2 μm to 12 μm.

[0055] A particle size of 2–12 μm for the negative electrode active material ensures a fast ion transport rate both within and between the particles, thereby further mitigating the degradation of battery rate performance caused by sodium additives and improving cycle performance. If the particle size c of the negative electrode active material is greater than 12 μm, the battery's internal resistance increases, resulting in poor cycle performance; if the particle size c is less than 2 μm, the small particle size reduces the battery's initial efficiency. Specifically, the particle size c of the negative electrode active material can be 3 μm, 4 μm, 5 μm, 5.5 μm, 6 μm, 7.5 μm, 8 μm, 9 μm, 10 μm, 12 μm, etc., as long as c is within the range of 3 μm–12 μm.

[0056] In some preferred embodiments, the particle size c of the negative electrode active material ranges from 3 μm to 9 μm.

[0057] When the particle size c of the negative electrode active material is within the above-mentioned preferred range, it can better improve the sodium ion transport efficiency and improve the cycle performance of the battery.

[0058] In some embodiments, the additive further includes 1,3-propanesulfonate lactone, wherein the mass content of 1,3-propanesulfonate lactone in the non-aqueous electrolyte is 0.5% to 2%.

[0059] Specifically, a 1,3-propanesulfonate lactone (PS) content of 0.5%–2% by mass in the electrolyte can effectively suppress side reactions on the positive electrode surface, as well as the dissolution and precipitation of metal ions, stabilize the positive electrode crystal structure, effectively reduce battery internal resistance and gas production, and improve cycle performance. Conversely, if the PS content in the electrolyte is below 0.5%, it cannot effectively suppress the dissolution and precipitation of metal ions at the positive electrode interface. If the PS content in the electrolyte is above 2%, the thickness of the electrode interface film formed in the electrolyte increases, leading to increased battery impedance. The mass content of 1,3-propanesulfonate lactone in the electrolyte can be 0.5%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9%, 2.0%, etc., as long as it is between 0.5% and 2%.

[0060] In some preferred embodiments, the 1,3-propanesulfonic acid lactone has a mass content of 1% to 2% in the non-aqueous electrolyte.

[0061] Within this preferred range, the mass content of 1,3-propanesulfonic acid lactone can effectively suppress the dissolution and precipitation of metal ions at the positive electrode interface, while also participating in the formation of a structurally stable interface film, thereby reducing the battery's internal resistance and gas production.

[0062] In some embodiments, the non-aqueous electrolyte further includes an electrolyte salt, which includes at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, and sodium bis(trifluoromethanesulfonyl)imide.

[0063] Based on the mass of the electrolyte as 100%, the mass content of the electrolyte salt is 8% to 14%.

[0064] Adding electrolyte salts to the electrolyte ensures that the electrolyte has high ionic conductivity and promotes the redox reaction of the battery.

[0065] In some embodiments, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of 1,4-butanesulfonate lactone, acrylate lactone (RPS), vinyl sulfate (DTD), and fluoroethylene carbonate, wherein the mass content of the auxiliary additives is 2.5% to 10% of the electrolyte by mass.

[0066] In some embodiments, the non-aqueous electrolyte further includes a non-aqueous organic solvent, which includes at least one of carbonates having 3 to 5 carbon atoms, carboxylic acid esters having 2 to 6 carbon atoms, and ethers having 4 to 10 carbon atoms.

[0067] Preferably, the carbonate solvent with 3 to 5 carbon atoms includes cyclic carbonates or chain carbonates with 3 to 5 carbon atoms. Cyclic carbonates include, but are not limited to, at least one of ethylene carbonate (EC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC). Chain carbonates may specifically include, but are not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC).

[0068] Preferably, the carboxylic acid esters having 2 to 6 carbon atoms include, but are not limited to, at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, and propyl propionate (PP). As a preferred embodiment, the non-aqueous electrolyte of the secondary battery further includes vinylene carbonate (VC), ethylene ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0069] Preferably, the ether solvent with 4 to 10 carbon atoms includes cyclic ethers or chain ethers with 4 to 10 carbon atoms. The cyclic ethers include, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ethers include, but are not limited to, at least one of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (TEGDME).

[0070] In some embodiments, the positive electrode active material layer includes a positive electrode active substance, which is selected from at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds;

[0071] The negative electrode includes a negative electrode active material, which includes one or more of carbon-based materials, silicon-based materials, and tin-based materials. The carbon-based material includes at least one of hard carbon, soft carbon, carbon nanotubes, graphite, graphene, expanded graphite, or mesophase carbon microspheres.

[0072] In some embodiments, the layered transition metal oxide has the chemical formula Na. n L m O r , 0 < n ≤ 1, 0 < m ≤ 1, 1 < r ≤ 2, L can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

[0073] In a preferred embodiment, the layered transition metal oxide has the chemical formula Na. p Ni m Mn n M (1-m-n) O q , where 0 < p ≤ 1, 0 ≤ m < 1, 0 < m + n < 1, 1 < q ≤ 2.

[0074] In a more preferred embodiment, the positive electrode active material is Na. p＇ Ni m＇ Mn n＇ Fe (1-m＇-n＇) O2, where 0 < p' ≤ 1, 0 ≤ m' < 1, 0 < m' + n' < 1, 1 < q' ≤ 2. Further, NaNi is preferred. 0.3 Mn 0.3 Fe 0.4 O2, NaNi 0.4 Mn 0.4 Fe 0.2 O2, NaNi 0.5 Mn 0.35 Fe0.15 O2.

[0075] In a more preferred embodiment, the layered transition metal oxide has the chemical formula NaNi. m Co n Mn p At least one of O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1).

[0076] In some embodiments, the molecular formula of the Prussian-like compound is Na. x＇ M[M′(CN)6] y＇ ·z'H2O, M is a transition metal, M′ is a transition metal, 0 <x'≤2,0<y'≤1,0<z'≤20。

[0077] In a more preferred embodiment, the Prussian-like compound is Na. x＇ Mn[Fe(CN)6] y＇ ·z'H2O or Na x＇ Fe[Fe(CN)6] y '·z'H2O, 0<x'≤2, 0<y'≤1, 0<z'≤20.

[0078] In some embodiments, the phosphate compound has the chemical formula Na3(RO) 1-x＇＇ PO4)2F 1+2x＇＇ Or Na2R′PO4F, where 0≤x′′≤1, R is selected from at least one of Al, V, Ge, Fe, and Ga, and R′ is selected from at least one of Fe and Mn.

[0079] In a more preferred embodiment, the chemical formula of the phosphate compound is Na3(VPO4)2F3, Na3(VOPO4)2F, Na2FePO4F, or Na2MnPO4F.

[0080] In some embodiments, the sulfate compound has the chemical formula Na2A(SO4)2·2H2O, where A is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0081] The present invention will be further illustrated by the following examples.

[0082] Example 1

[0083] This embodiment is used to illustrate the sodium-ion battery disclosed in this application.

[0084] (1) Preparation of positive electrode: Take the positive electrode active material NaNi in a mass ratio of 88.825:6.175:2:3 0.3 Fe0.3 Mn 0.4 O2, sodium-supplementing additive Na5NbO5, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed and then dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. The obtained slurry is uniformly coated on both sides of aluminum foil, dried, calendered, and vacuum dried, and then aluminum leads are welded on using an ultrasonic welding machine to obtain the positive electrode sheet. The total mass of the positive electrode active material and sodium-supplementing additive is 100%, and the mass content of the sodium-supplementing additive is 'a', where 'a' is 6.5%.

[0085] (2) Preparation of negative electrode: Hard carbon, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5 and then dispersed in an appropriate amount of deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, calendered, and vacuum dried, and nickel leads were welded on using an ultrasonic welding machine to obtain the negative electrode sheet. The particle size of the hard carbon, the negative electrode active material, is c, and the specific value of c is shown in Table 1.

[0086] (3) Preparation of electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate were mixed in a mass ratio of EC:PC:EMC = 10:15:75. Then, sodium hexafluorophosphate (12% by mass) was added, sodium difluorooxalate borate (b) was added, and 1,3-propanesulfonate lactone (PS) was added. Finally, auxiliary additives were added to form the electrolyte. The specific types and mass contents of auxiliary additives, the specific value of b, and the mass content of 1,3-propanesulfonate lactone are shown in Table 1.

[0087] (4) Preparation of sodium-ion battery: A separator is placed between the positive electrode and the negative electrode prepared above. Then, the sandwich structure composed of the positive electrode, the negative electrode and the separator is wound up. The wound body is flattened and put into an aluminum foil packaging bag for assembly to obtain the battery.

[0088] Examples 2-31 and Comparative Examples 1-11

[0089] The differences between Examples 2-31 and Comparative Examples 1-11 and Example 1 are that the values ​​of a, c, and b are different, as are the types and mass contents of the auxiliary additives and the mass content of 1,3-propanesulfonic acid lactone, as detailed in Table 1. The rest of the preparation method is the same as in Example 1. Among the auxiliary additives, DTD is vinyl sulfate and RPS is acrylate lactone.

[0090] Table 2. Parameters for Examples and Comparative Examples

[0091]

[0092]

[0093] Performance testing

[0094] The sodium-ion batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests.

[0095] 1. Initial effectiveness test:

[0096] Place the battery in a 25℃ environment and let it stand for 2 hours. Charge it at a constant current rate of 0.5C to 4.0V, and then charge it at a constant voltage rate to a current of 0.03C. Record the charging capacity C1. Discharge it at a constant current rate of 1C to 1.5V and record the discharge capacity C2.

[0097] First-efficacy (%) = C2 / C1 × 100%.

[0098] 2. High-temperature cycling performance test:

[0099] After formation, the battery was placed at 45°C and left to stand for 2 hours. It was then charged at a constant current rate of 0.5C to 4.0V, and then charged at a constant voltage rate to a current of 0.03C. Finally, it was discharged at a constant current rate of 1C to 1.5V. The discharge capacity C3 of the first cycle was recorded. After 400 cycles of charge and discharge, the discharge capacity C4 of the 400th cycle was recorded.

[0100] Capacity retention rate (%) after 400 high-temperature cycles = C4 / C3 × 100%.

[0101] The battery gas production rate was tested by measuring the weight of the displaced liquid to calculate the battery gas production rate. During the first week of charging and discharging, after the battery was fully charged, the weight of the displaced liquid, G1, was measured and recorded. In the 400th week, after the battery was fully charged, the weight of the displaced liquid, G2, was measured and recorded.

[0102] Gas production (mL) of battery after 400 high-temperature cycles = G2 - G1.

[0103] 3. Room temperature cycling performance test:

[0104] After formation, the battery was placed at 25°C and left to stand for 2 hours. It was then charged at a constant current rate of 0.5C to 4.0V, and then charged at a constant voltage rate to a current of 0.03C. Finally, it was discharged at a constant current rate of 1C to 1.5V. The discharge capacity C3 of the first cycle was recorded. After 400 cycles of charge and discharge, the discharge capacity C4 of the 400th cycle was recorded.

[0105] Capacity retention rate (%) after 400 cycles at room temperature = C4 / C3 × 100%.

[0106] 4. Conductivity test:

[0107] The conductivity test follows standard HG / T 4067-2015. The conductivity meter used is a DDSJ-308A instrument with a range of 0.000 μS / cm to 199.9 mS / cm, and type 1 and type 10 electrodes (platinum black). Before use, it is calibrated with a potassium chloride standard solution at 25℃: C(KCl) = 0.1 mol / L (standard value 12.88 mS / cm). During testing, the electrodes and temperature sensor are inserted into a beaker containing the electrolyte. The beaker is placed in a constant temperature bath and kept at 25℃. The reading is taken after the reading stabilizes.

[0108] 5. DCIR test after battery capacity grading

[0109] At 25℃, the battery is left to rest for 5 minutes, then charged at a constant current rate of 1C to the upper limit cutoff voltage, and then charged at a constant voltage until the current is less than or equal to 0.05C. At this point, the battery's state of charge (SOC) is 100%. After resting for 5 minutes, it is discharged at a constant current rate of 1C to adjust the SOC of the sodium-ion secondary battery to 50%. After resting for 30 minutes, it is discharged at a rate of 1C for 10 seconds. The voltage before discharge is recorded as U1, and the voltage after discharge is recorded as U2. Then, the battery's DCIR = (U1 - U2) / 1C.

[0110] 6. Battery internal resistance

[0111] The battery's internal resistance was tested after the first full charge. Specifically, at 25°C, the battery was charged at a constant current rate of 1C to the upper limit cutoff voltage, and then charged at a constant voltage until the current was less than or equal to 0.05C. At this point, the battery's state of charge (SOC) was 100%, and the battery's internal resistance was tested.

[0112] The test results are shown in Table 2-5.

[0113] Table 2 Performance data for Examples 1-17 and Comparative Examples 1-11

[0114]

[0115]

[0116] As shown in Tables 1 and 2, compared with Comparative Examples 1-3, Example 1, without sodium-supplementing additives or sodium salt additives, resulted in low initial efficiency, high internal resistance, and poor cycle performance. Comparative Example 2, with the addition of sodium-supplementing additives, showed a slight improvement in initial efficiency, but the battery performance remained poor. Comparative Example 3, without sodium-supplementing additives but with the addition of sodium salt additives to the electrolyte, improved electrolyte conductivity, but still resulted in low initial efficiency, high internal resistance, and poor cycle performance. This indicates that adding sodium-supplementing additives can supplement sodium and improve initial efficiency; adding sodium salt additives helps improve electrolyte conductivity. Comparing Example 7 with Comparative Examples 4-5, Example 7 with a sodium-supplementing additive content (a) below 5% resulted in low initial efficiency; Example 7 with a sodium-supplementing additive content (a) above 10% resulted in low initial efficiency, high DCIR, high internal resistance, and poor cycle performance. It is speculated that when the sodium-supplementing additive content (a) exceeds 10%, the additive decomposes, and residual byproducts damage the interfacial film, increasing internal resistance and reducing initial efficiency and cycle performance. Compared with Comparative Examples 5-6, in Example 1, the mass content (b) of sodium salt-type sodium supplementation additive in the electrolyte was less than 1%, resulting in low electrolyte conductivity and increased battery internal resistance. When b was greater than 10%, although electrolyte conductivity improved, battery internal resistance remained high and cycle performance was poor. It is speculated that adding sodium salt-type sodium supplementation additive (b) to the electrolyte at a concentration between 1% and 10% can improve electrolyte conductivity and participate in the formation of the electrode interface film, protecting the positive and negative electrodes. This effectively solves the problems of poor conductivity of sodium supplementation additives and the destructive effects of residual byproducts on the positive and negative electrodes. Compared with Comparative Examples 8-9, in Examples 6-7, the particle size (c) of the negative electrode active material was less than 2 μm or greater than 12 μm, resulting in low initial efficiency, high DCIR, high internal resistance, low cycle capacity retention, and excessive gas production. Comparing Examples 1-17 and Comparative Examples 10-11, although the mass content of sodium additive a is between 5% and 10%, the mass content of sodium salt additive b is between 1% and 10%, and the particle size c of the negative electrode active material is between 2 and 12 μm, the values ​​of a, b, and c do not satisfy the relationship 0.3≤a / (b+c)≤1.5. This results in low initial efficiency, poor cycle performance, high internal resistance, and high DCIR impedance after capacity grading. This indicates that in the battery, a, b, and c must not only satisfy 5≤a≤10, 1≤b≤10, and 2≤c≤12, but also 0.3≤a / (b+c)≤1.5 to effectively improve the conductivity of the electrolyte and the diffusion and transport rate of ions in the negative electrode material while ensuring optimal conductivity of the positive electrode. This can effectively reduce the overall internal resistance of the battery and improve its initial efficiency and cycle performance.

[0117] Comparisons of Examples 1-4 show that, with the total mass of the positive electrode active material and sodium-supplementing additive as 100%, and the mass content of the sodium-supplementing additive being 'a', and 'a' being in the range of 5.5% to 9%, the battery exhibits higher initial efficiency, higher capacity retention during both room temperature and high temperature cycling, and lower internal resistance. Comparisons of Examples 5-9 show that, with the added sodium salt additive having a mass content 'b' in the electrolyte between 2% and 6%, the battery exhibits relatively high conductivity in the electrolyte, lower internal resistance, and higher cycle capacity retention. Comparisons of Examples 10-13 show that, with the negative electrode active material particle size 'c' in the range of 3 to 9 μm, the battery exhibits higher initial efficiency, lower DCIR, higher cycle capacity retention, lower gas production, and lower internal resistance. By comparing Examples 1-17, the values ​​of a, b, and c in the battery satisfy the range of 5≤a≤10, 1≤b≤10, and 2≤c≤12, and also satisfy 0.5≤a / (b+c)≤1.2. The battery has high initial efficiency and cycle performance, and low internal resistance.

[0118] Comparing Example 1 and Example 17, Example 17's electrolyte lacked 1,3-propanesulfonate additive, resulting in low battery cycle capacity retention, excessive gas production, and low first-time efficiency. This indicates that adding 1,3-propanesulfonate (PS) to the electrolyte can effectively suppress side reactions on the positive electrode surface, as well as the dissolution and precipitation of metal ions, stabilize the positive electrode crystal structure, effectively reduce battery internal resistance and gas production, and improve cycle performance.

[0119] Table 3 Battery performance data for Examples 1 and 18-21

[0120]

[0121] As shown in Tables 1 and 3, compared with Examples 18-21, the initial efficiency, internal resistance, DCIR, cycle capacity retention, and gas production of the batteries were basically similar even when different types of sodium-supplementing additives were added to the batteries in Example 1. This indicates that as long as the sodium-supplementing additive meets the Na... x M y O z The compounds shown in Formula 1, wherein 0.2 < x / y < 9, 0 < y < 6, 2 ≤ z ≤ 9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr, all have the effect of improving the first efficiency and cycle performance of the battery and reducing the internal resistance of the battery.

[0122] Table 4 Battery performance data for Examples 1 and 22-23

[0123]

[0124] As shown in Tables 1 and 4, compared with Examples 22-23, the battery's initial efficiency, internal resistance, DCIR, cycle capacity retention rate, and gas production were basically similar when different types of sodium salt additives were added to the electrolyte in Example 1. This indicates that the different types of sodium salt additives provided in this application all have the effect of improving the battery's initial efficiency and cycle performance, and reducing the battery's internal resistance.

[0125] Table 5 Battery performance data for Examples 1 and 24-31

[0126]

[0127] As shown in Tables 1 and 5, compared with Examples 24-28, the batteries with higher DCIR, higher internal resistance, higher gas production, and lower cycle capacity retention when the mass content of 1,3-propanesulfonate added to the electrolyte in Examples 27-28 was not in the range of 0.5% to 2% were compared in Examples 1. This indicates that adding 1,3-propanesulfonate (PS) to the electrolyte in the range of 0.5% to 2% can effectively suppress the occurrence of side reactions on the electrode surface and the dissolution and precipitation of metal ions, stabilize the positive electrode crystal structure, effectively reduce the battery's internal resistance and gas production rate, and improve cycle performance. When the PS content added to the electrolyte is in the range of 1% to 2%, the battery's internal resistance and gas production rate are lower.

[0128] Comparing Example 1 with Examples 29-30, the addition of 1,3-propanesulfonate lactone and auxiliary additives to the electrolyte in Examples 29-30 resulted in a decrease in battery DCIR and internal resistance, a significant decrease in cycle gas production, an increase in first-efficiency, and an improvement in cycle capacity retention. This indicates that the addition of 1,3-propanesulfonate lactone to the electrolyte, in synergy with auxiliary additives, has the effect of reducing battery DCIR, internal resistance, and gas production, and improving battery first-efficiency and cycle performance.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium-ion battery, characterized in that, The device includes a non-aqueous electrolyte, a positive electrode, and a negative electrode. The non-aqueous electrolyte includes additives, including sodium salt additives. The positive electrode includes a positive electrode active material layer, which includes a sodium-supplementing additive and a positive electrode active material. The sodium-supplementing additive is a sodium-rich transition metal oxide. The negative electrode includes a negative electrode active material. The sodium-ion battery satisfies the following relationship: 0.3≤a / (b+c)≤1.5, and 5≤a≤10, 1≤b≤10, 2≤c≤12; Wherein, the total mass of the sodium supplement additive and the positive electrode active material is 100%, and a is the mass content of the sodium supplement additive, in % %. b represents the mass content of the sodium salt additive in the non-aqueous electrolyte, in percentage (%). c represents the particle size of the negative electrode active material, in μm. The sodium salt type additive includes one or more of sodium difluorosulfonylimide, sodium difluorooxalate borate, and sodium difluorophosphate. The additive also includes 1,3-propanesulfonic acid lactone, wherein the mass content of 1,3-propanesulfonic acid lactone in the non-aqueous electrolyte is 0.5% to 2%.

2. The sodium-ion battery according to claim 1, characterized in that, The sodium-ion battery satisfies the following relationship: 0.5≤a / (b+c)≤1.

2.

3. The sodium-ion battery according to claim 1, characterized in that, The total mass of the sodium supplement additive and the positive electrode active material is 100%, and the mass content a of the sodium supplement additive is in the range of 5.5% to 9%.

4. The sodium-ion battery according to claim 1, characterized in that, The mass content b of the sodium salt additive in the non-aqueous electrolyte ranges from 2% to 6%.

5. The sodium-ion battery according to claim 1, characterized in that, The particle size c of the negative electrode active material ranges from 3 μm to 9 μm.

6. The sodium-ion battery according to claim 1, characterized in that, The mass content of the 1,3-propanesulfonic acid lactone in the non-aqueous electrolyte is 1% to 2%.

7. The sodium-ion battery according to claim 1, characterized in that, The sodium-rich transition metal oxide includes the compound shown in Formula 1. Na x M y O z Formula 1 Wherein, 0.2 < x / y < 9, 0 < y < 6, 2 ≤ z ≤ 9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr.

8. The sodium-ion battery according to claim 7, characterized in that, The sodium-rich transition metal oxide includes one or more of Na5NbO5, Na3NbO4, Na4Nb2O7, Na5VO5, Na3VO4, and Na3TaO4.

9. The sodium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte also includes electrolyte salts, auxiliary additives, and non-aqueous organic solvents. The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium trifluoromethanesulfonylimide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, and sodium bis(trifluoromethanesulfonyl)imide. Based on the mass of the electrolyte as 100%, the mass content of the electrolyte salt is 8% to 14%. The auxiliary additives include at least one of 1,4-butanesulfonate lactone, acrylate lactone, vinyl sulfate, and fluorovinyl carbonate. With the electrolyte comprising 100% by mass, the auxiliary additives comprise 2.5% to 10% by mass. The non-aqueous organic solvent includes at least one of carbonates with 3 to 5 carbon atoms, carboxylic acid esters with 2 to 6 carbon atoms, and ethers with 4 to 10 carbon atoms; The positive electrode active material includes at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds; The negative electrode includes a negative electrode active material, which includes one or more of carbon-based materials, silicon-based materials, and tin-based materials.

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