Sodium ion battery

Abstract

The invention relates to the technical field of electrochemistry, in particular to a sodium ion battery. The sodium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the negative electrode comprises a negative electrode material layer, the non-aqueous electrolyte comprises a sodium salt, a solvent and an additive, the additive comprises a sulfur-containing compound and silane phosphate, and the silane phosphate is selected from a compound as shown in a structural formula 1; the sodium ion battery satisfies the following conditions: 0.2 < = (a + b) / c < = 3.5, 0.1 < = a < = 2, 0.1 < = b < = 1, and 0.85 < = c < = 1.15. By limiting the relationship among the content a of the compound as shown in the structural formula 1, the content b of the sulfur-containing compound and the compaction density c of the negative electrode material layer, the impedance of the battery can be effectively reduced, the gas production of the battery is reduced, and the low-temperature and rate performance of the sodium-ion battery is improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and in particular to a sodium-ion battery with excellent low-temperature performance and rate performance. Background Technology

[0002] Sodium-ion batteries, similar in principle and structure to lithium-ion batteries, utilize an electrolyte medium that conducts alkali metal ions to facilitate reversible shuttle transport of these ions between two electrodes. Compared to lithium-ion batteries, sodium-ion batteries offer greater resource availability, lower cost, and less price fluctuations. Their wide temperature range and high safety also make them a viable alternative. With continuous advancements in sodium-ion battery technology, they are poised to occupy a significant position in my country's energy system, particularly in the energy storage sector, where they possess vast growth potential. Therefore, developing high-performance, low-cost sodium-ion batteries is crucial for their industrialization. However, existing sodium-ion batteries suffer from poor low-temperature and rate performance, as well as high gas production, hindering their development and application. Therefore, addressing these technical challenges is a key research focus in this field. Summary of the Invention

[0003] To address the above technical problems, this invention provides a sodium-ion battery that overcomes the issues of poor low-temperature performance and rate performance, and high gas production in existing sodium-ion batteries by adjusting the composition of additives in the non-aqueous electrolyte and the structure of the negative electrode material layer.

[0004] The present invention adopts the following technical solution:

[0005] A sodium-ion battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte;

[0006] The negative electrode includes a negative electrode material layer;

[0007] The non-aqueous electrolyte comprises a sodium salt, a solvent, and additives, wherein the additives include a sulfur-containing compound and a compound represented by structural formula 1:

[0008]

[0009] Structural Formula 1

[0010] R1, R2, and R3 are each independently selected from halogen-substituted or unsubstituted C2-C5 alkyl, halogen-substituted or unsubstituted C2-C5 alkenyl, halogen-substituted or unsubstituted C2-C5 alkynyl, or -Si(R4)3. R4 is selected from C2-C5 alkyl, and at least one of R1, R2, and R3 is selected from -Si(R4)3.

[0011] The sodium-ion battery meets the following conditions:

[0012] 0.2≤(a+b) / c≤3.5, 0.1≤a≤2, 0.1≤b≤1, 0.85≤c≤1.15;

[0013] Where: a is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in wt%;

[0014] b represents the mass percentage of sulfur-containing compounds in the non-aqueous electrolyte, in wt%.

[0015] c represents the compaction density of the negative electrode material layer, in g / cm³. 3 .

[0016] The sodium-ion battery of this invention uses the compound shown in structural formula 1 and a sulfur-containing compound as additives. Through extensive research, the inventors discovered that when the mass percentage *a* of the compound shown in structural formula 1 in the non-aqueous electrolyte, the mass percentage *b* of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density *c* of the negative electrode material layer satisfy the following relationships: 0.2 ≤ (a+b) / c ≤ 3.5, 0.1 ≤ a ≤ 2, 0.1 ≤ b ≤ 1, 0.85 ≤ c ≤ 1.15, the battery impedance can be effectively reduced, battery gas production can be reduced, and the low-temperature and rate performance of the sodium-ion battery can be effectively improved. It is speculated that the compound shown in structural formula 1 forms a film on the surface of the battery negative electrode, which can reduce battery impedance. Furthermore, because the SEI film formed is more stable, it further suppresses the side reactions of electrolyte decomposition caused by the contact between the non-aqueous electrolyte and the positive and negative electrode active materials, significantly improving the stability of the electrode and electrolyte, and improving low-temperature performance. Simultaneously, sulfur-containing compounds can participate in the SEI film formation of the negative electrode earlier than other components of the electrolyte, improving the film quality, increasing the transport rate of sodium ions on the interface film, reducing electrolyte decomposition, effectively improving battery cycle stability and rate performance, and further reducing battery gas production. Furthermore, by limiting the compaction density of the negative electrode material layer, sufficient contact between particles can be ensured without blocking ion movement channels, which is beneficial for the compound shown in Formula 1 to participate in the SEI film formation on the surface of the negative electrode material. This ensures good conductivity and rapid ion movement of electrons during high-current discharge, reducing discharge polarization, lowering impedance, and further improving the battery's rate performance. When the mass percentage a of the compound shown in Formula 1 in the non-aqueous electrolyte, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer are in a synergistic state, the battery stability can be significantly improved, rate performance enhanced, impedance reduced, and gas production decreased.

[0017] When the relationship (a+b) / c > 3.5 between the mass percentage a of the compound represented by structural formula 1 in the non-aqueous electrolyte, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer, it may be that the content of the compound represented by structural formula 1 or the sulfur-containing compound in the non-aqueous electrolyte is too high, which leads to an increase in the viscosity of the non-aqueous electrolyte, excessive consumption of electrolyte to participate in film formation, high impedance, and poor low-temperature and rate performance; it may also be that the compaction density of the negative electrode material layer is too low, which leads to an excessively large interparticle distance, reduced conductivity, and deterioration of low-temperature and cycle performance.

[0018] When the relationship (a+b) / c < 0.2 between the mass percentage a of the compound represented by structural formula 1 in the non-aqueous electrolyte, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer, it may be that the content of the compound represented by structural formula 1 or the sulfur-containing compound in the non-aqueous electrolyte is too small, which cannot effectively participate in film formation, resulting in poor film quality and deteriorated rate performance; it may also be that the compaction density of the negative electrode material layer is too large, resulting in too small distance between particles, and longer time for ions to pass through the negative electrode, thus deteriorating rate performance.

[0019] Preferably, the relationship between the mass percentage a of the compound represented by structural formula 1 in the non-aqueous electrolyte, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer satisfies 0.4≤(a+b) / c≤1.6.

[0020] Specifically, in some embodiments of the present invention, the compound shown in Structural Formula 1 acts as an additive, participating in the film formation on the negative electrode surface. This suppresses side reactions caused by the contact between the non-aqueous electrolyte and the positive and negative electrode active materials, improving the stability of the electrode and electrolyte, reducing gas production, and thus improving the low-temperature and rate performance of the battery. If the value of 'a' is too small, it cannot effectively participate in the negative electrode film formation, resulting in poor film quality and poor stability of the SEI film, which accelerates side reactions, increases gas production, and degrades battery performance. If the value of 'a' is too large, a large amount of the compound shown in Structural Formula 1 participates in the film formation, causing a significant increase in battery impedance, a decrease in conductivity, and an increase in viscosity, thereby degrading the low-temperature performance of the battery. More specifically, the mass percentage 'a' of the compound represented by structural formula 1 is within the range of any value consisting of 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, or more; preferably, the mass percentage 'a' of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.2 to 1 wt%.

[0021] Specifically, in some embodiments of the present invention, R1, R2, and R3 are the same in the compound represented by structural formula 1.

[0022] More specifically, in some embodiments of the present invention, the compound represented by structural formula 1 includes one or more of the following compounds:

[0023]

[0024] Specifically, in some embodiments of the present invention, using sulfur-containing compounds as additives helps improve the quality of the negative electrode film formation, increases the transport rate of sodium ions on the interfacial film, and reduces electrolyte decomposition. If the b value is too small, fewer additives participate in film formation, resulting in low electrolyte conductivity and poor low-temperature and rate performance; if the b value is too large, too many additives participate in film formation, increasing the reaction with the electrolyte, causing a sharp increase in electrolyte impedance, and degrading battery rate and low-temperature performance. More specifically, the mass percentage b of the sulfur-containing compound is within the range of 0.1wt%, 0.15wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, or any value above; preferably, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte is 0.2 to 0.5wt%.

[0025] Specifically, in some embodiments of the present invention, the sulfur-containing compound includes at least one of cyclic sulfate esters and sulfonate lactones;

[0026] In a preferred embodiment, the cyclic sulfate compound includes at least one of 4-methyl vinyl sulfate, vinyl sulfate (DTD), and propylene sulfate (TS);

[0027] In a preferred embodiment, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone (PS), 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone (RPS).

[0028] Specifically, in some embodiments of the present invention, limiting the compaction density of the negative electrode material layer allows for sufficient contact between particles without blocking ion movement channels. This facilitates the participation of additives in SEI film formation on the surface of the negative electrode material, ensuring good conductivity and rapid ion movement during high-current discharge, reducing discharge polarization, lowering impedance, and further improving the battery's rate performance. If the c value is too small, the distance between particles is too large, reducing the contact probability and contact area, decreasing conductivity, and deteriorating low-temperature and cycle performance. If the c value is too large, the distance between particles is too small, hindering the rapid movement of a large number of ions, deteriorating the battery's rate performance, and reducing discharge capacity. More specifically, the compaction density c of the negative electrode material layer is 0.85 g / cm³.3 0.88g / cm 3 0.9g / cm 3 0.92g / cm 3 0.95g / cm 3 0.98g / cm 3 1g / cm 3 1.02g / cm 3 1.05g / cm 3 1.08g / cm 3 1.1g / cm 3 1.12 g / cm 3 1.15g / cm 3 Preferably, the compaction density of the negative electrode material layer is 0.9–1 g / cm³. 3 .

[0029] Specifically, in some embodiments of the present invention, the sodium salt includes one or more of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]), or sodium bis(trifluoromethanesulfonyl)imide (Na[(CF3SO2)2N]).

[0030] Specifically, in some embodiments of the present invention, the organic solvent includes at least one of cyclic carbonates, linear carbonates, carboxylic acid esters, and ether compounds.

[0031] In some preferred embodiments, the cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, vinylene carbonate, propylene carbonate, and butene carbonate.

[0032] In some preferred embodiments, the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0033] In some preferred embodiments, the carboxylic acid ester includes at least one selected from methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0034] In some preferred embodiments, the ether compound includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0035] Specifically, in some embodiments of the present invention, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of cyclic carbonate compounds, borate compounds, and nitrile compounds;

[0036] The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 2:

[0037]

[0038] In the structural formula 2 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group;

[0039] In some preferred embodiments, the compound represented by structural formula 2 includes at least one of the compounds represented by compounds 2-1 to 2-6 below:

[0040]

[0041] The borate ester compounds include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; and / or,

[0042] The nitrile compounds are selected from one or more of succinic anionibacterium, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, and sebaconitil.

[0043] Specifically, in some embodiments of the present invention, based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01 wt% to 10 wt%. Preferably, the content is 0.1 wt% to 5 wt%; more preferably, the content is 0.1 wt% to 2 wt%. Specifically, the content of any one optional substance in the auxiliary additive can be 0.01 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.5 wt%, or 5 wt%.

[0044] Specifically, in some embodiments of the present invention, the negative electrode material layer includes a negative electrode active material, which includes artificial graphite, natural graphite, and SiO2. w At least one of the silicon-carbon composite materials formed by combining graphite, wherein 0 ≤ w < 2.

[0045] Specifically, in some embodiments of the present invention, the negative electrode further includes a negative electrode conductive agent, which is selected from one or more of acetylene black, Super P, graphene, Ketjen black, SFG-6, carbon nanotubes, and graphyne.

[0046] Specifically, in some embodiments of the present invention, the negative electrode further includes a negative electrode binder, which is selected from one or more of the following: polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ether, copolymers of ethylene-tetrafluoroethylene, copolymers of vinylidene fluoride-tetrafluoroethylene, copolymers of vinylidene fluoride-trifluoroethylene, copolymers of vinylidene fluoride-trichloroethylene, copolymers of vinylidene fluoride-fluorinated vinylidene, copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0047] Specifically, in some embodiments of the present invention, the positive electrode includes a positive electrode active material, which is selected from one or more of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

[0048] Specifically, in some embodiments of the present invention, the chemical formula of the layered transition metal oxide is Na. x M y O z 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, M can be selected from one or more of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; the transition metal oxide is NaNi. m Fe n Mn p O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1), NaNi m Co n Mn p O2 (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1); more specifically, the layered transition metal oxide is selected from Na[Cu 1 / 9Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2, Na 0.44MnO2, NaNi 0.3 Mn 0.3 Fe 0.4 O2, Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 O2, Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na 7 / 9 [Cu 2 / 9 Fe 1 / 9 Mn 2 / 3 O2, NaNi 0.7 Co 0.15 Mn 0.15 One or more of O2.

[0049] In some embodiments of the present invention, the formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, where M is a transition metal, M′ is a transition metal, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; the Prussian compound is Na x Mn[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20), and the Prussian compound is Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20).

[0050] In some embodiments of the present invention, the chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, and M is selected from one or more of Al, V, Ge, Fe, Ga; the chemical formula of the phosphate compound is Na3(VPO4)2F3, Na3(VOPO4)2F.

[0051] In some embodiments of the present invention, the chemical formula of the phosphate compound is Na2MPO4F, and M is selected from one or more of Fe, Mn; the chemical formula of the phosphate compound is Na2FePO4F, Na2MnPO4F.

[0052] In some embodiments of the present invention, the chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, and M can be selected from one or more of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

[0053] Specifically, in some embodiments of the present invention, the positive electrode further includes a positive electrode conductive agent and a positive electrode binder, which may be the same as the negative electrode binder and negative electrode conductive agent, respectively, and will not be described in detail here.

[0054] In some embodiments of the present invention, the sodium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0055] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0056] Compared with the prior art, the present invention achieves the following beneficial effects:

[0057] The sodium-ion battery of the present invention uses sulfur-containing compounds and compounds shown in structural formula 1 as electrolyte additives. By limiting the relationship between the content a of the compound shown in structural formula 1, the content b of the sulfur-containing compound, and the compaction density c of the negative electrode material layer, the battery impedance can be effectively reduced, the battery gas production can be reduced, and the low-temperature and rate performance of the sodium-ion battery can be improved. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0059] In the embodiments and comparative examples of the present invention, one of the compounds shown in Table 1 is used as a non-aqueous electrolyte additive.

[0060] Table 1

[0061]

[0062] Examples 1-21

[0063] This embodiment provides a sodium-ion battery, which includes a positive electrode, a negative electrode, and a non-aqueous electrolyte.

[0064] (1) Preparation of non-aqueous electrolyte

[0065] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. 1 mol / L sodium hexafluorophosphate was added. Based on 100% of the total weight of the electrolyte, additives of the types and mass percentages shown in Table 1 were added.

[0066] (2) Preparation of positive electrode plate

[0067] Take the positive electrode active material NaNi according to a mass ratio of 88:9:3 0.3 Mn 0.3 Fe 0.4 O2, 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, and after drying, rolling and vacuum drying, aluminum leads are welded on using an ultrasonic welding machine to obtain the positive electrode plate. The thickness of the electrode plate is between 120-150 μm.

[0068] (3) Preparation of negative electrode plate

[0069] Hard carbon, conductive carbon black Super-P, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) were mixed 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 then nickel leads were welded on using an ultrasonic welder to obtain a negative electrode plate with a thickness between 120-150 μm. The compaction density of the negative electrode material layer is shown in Table 1.

[0070] (4) Cell fabrication

[0071] A three-layer separator with a thickness of 20 μm is placed between the positive and negative plates prepared above. Then, the sandwich structure composed of the positive plate, negative plate and separator is wound up, and the wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the cell to be injected with electrolyte.

[0072] (5) Electrolyte injection and formation of the battery cell

[0073] In a glove box where the dew point is controlled below -40°C, the electrolyte prepared above is injected into the battery cell, vacuum sealed, and left to stand for 24 hours.

[0074] Then, the conventional formation of the battery is carried out according to the following steps: constant current charging at 0.1C for 180 minutes, constant current charging at 0.2C to 3.8V, vacuum sealing for the second time, and then further constant current charging at 0.2C to 3.95V. After being left at room temperature for 24 hours, constant current discharge at 0.2C to 1.5V is obtained to obtain a sodium-ion battery.

[0075] Comparative Examples 1-15

[0076] Comparative Examples 1-15 include most of the operating steps in the above embodiments, except that: the types and contents of the additives, and the compaction density of the negative electrode material layer, are calculated based on 100% of the total mass of the electrolyte, as shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] Note: DTD - vinyl sulfate, TS - propylene sulfate, PS - 1,3-propanesulfonate lactone, RPS - 1,3-propenesulfonate lactone, FEC - fluorovinyl carbonate, HTCN - 1,3,6-hexanetrionitrile

[0081] Performance testing

[0082] The electrolytes and sodium-ion batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0083] 1.4C rate discharge capacity ratio: The ratio of the capacity released by the battery from 3.95-1.5V at a 4C rate to the capacity released by the battery at a 0.2C rate during the activation phase.

[0084] 2. High temperature cycle test: After formation, the battery is left to stand at 45℃ for 2 hours, charged at a constant current rate of 0.5C to 3.95V, then charged at a constant voltage to a current of 0.03C, and then discharged at a constant current rate of 1C to 1.5V, and cycled 400 times.

[0085] Rate of volume change = (Volume of the last revolution - Volume of the first revolution) / Volume of the first revolution × 100%

[0086] Internal resistance growth rate = (Internal resistance of the last cycle - Internal resistance of the first cycle) / Internal resistance of the first cycle × 100%

[0087] 3. Low temperature test: At 25℃, the formed battery was charged to 4.25V with 1C constant current and constant voltage, and then discharged to 3.0V with 1C constant current and constant voltage. The discharge capacity was recorded. Then, the battery was charged to 4.25V with 1C constant current and constant voltage, placed in an environment of -20℃ for 12 hours, and then discharged to 3.0V with 0.5C constant current. The discharge capacity was recorded.

[0088] The discharge capacity ratio at -20℃ (%) = 0.5C discharge capacity (-20℃) / 1C discharge capacity (25℃) × 100%.

[0089] 4. Electrolyte conductivity: After placing the electrolyte in a -20℃ constant temperature chamber for 12 hours, its conductivity and viscosity were measured using a conductivity meter.

[0090] (1) The test results of Examples 1-12 and Comparative Examples 4-13 are shown in Table 3.

[0091] Table 3

[0092]

[0093]

[0094] As can be seen from the test results in Table 3, the sodium-ion battery of the present invention, by using the compound shown in structural formula 1 and the sulfur-containing compound as additives, and further limiting the mass percentage a of the compound shown in structural formula 1 in the non-aqueous electrolyte, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer, satisfies the following relationships: 0.2≤(a+b) / c≤3.5, 0.1≤a≤2, 0.1≤b≤1.

[0095] When 0.85≤c≤1.15, the battery impedance can be effectively reduced, the battery gas production can be reduced, and the low-temperature and rate performance of sodium-ion batteries can be effectively improved.

[0096] The test results of Example 1 and Comparative Examples 4-13 show that when any one of the following parameters—mass percentage a of the compound represented by Structural Formula 1 in the non-aqueous electrolyte, mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, or compaction density c of the negative electrode material layer—does not meet the specified range, or when the value of (a+b) / c is too large or too small, it cannot effectively improve the low-temperature and rate performance of the sodium-ion battery. This indicates that the mass percentage a of the compound represented by Structural Formula 1 in the non-aqueous electrolyte, mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and compaction density c of the negative electrode material layer are strongly correlated with improving the performance of the sodium-ion battery.

[0097] (2) The test results of Examples 1, 13-16 and Comparative Examples 14-15 are shown in Table 4.

[0098] Table 4

[0099]

[0100] As can be seen from the test results in Table 4, when different types of compounds of structural formula 1 are selected as electrolyte additives in the sodium-ion battery of the present invention, improvements in the low-temperature and rate performance of the lithium-ion battery can be achieved when the mass percentage a of the compound of structural formula 1, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer meet the corresponding conditions. This indicates that the battery system of the present invention has universality for different compounds of structural formula 1. However, as can be seen from the test results of Example 1 and Comparative Examples 14-15, when other silane phosphates are used, even if the content meets the corresponding conditions, they still cannot achieve a good improvement effect, indicating the specificity of the compound of structural formula 1 as an additive in improving the low-temperature performance of sodium-ion batteries.

[0101] (3) The test results of Examples 1 and 17-19 are shown in Table 5.

[0102] Table 5

[0103]

[0104] As can be seen from the test results in Table 5, when different types of sulfur-containing compounds are selected as electrolyte additives in the sodium-ion battery of the present invention, the low-temperature and rate performance of the lithium-ion battery can be improved when the mass percentage a of the compound shown in structural formula 1, the mass percentage b of the sulfur-containing compound in the non-aqueous electrolyte, and the compaction density c of the negative electrode material layer meet the corresponding conditions. This indicates that the battery system of the present invention has universality for different sulfur-containing compounds.

[0105] (4) The test results of Examples 1, 20-21, and Comparative Examples 1-3 are shown in Table 6.

[0106] Table 6

[0107]

[0108] As can be seen from the test results of Examples 1 and 20-21 in Table 6, the sodium-ion battery of the present invention, with the addition of additives such as fluoroethylene carbonate (FEC) and 1,3,6-hexanetrionitrile (HTCN) to the non-aqueous electrolyte, can further optimize the rate performance and low-temperature performance of the sodium-ion battery, indicating that there is a complementary effect between the compound shown in structural formula 1 and other additives.

[0109] The test results of Example 1 and Comparative Examples 1-3 show that when the non-aqueous electrolyte does not contain the compound shown in Structural Formula 1, or when conventional additives are used to replace the compound shown in Structural Formula 1, the rate performance and low-temperature performance of the sodium-ion battery are poor. This indicates that the sodium-ion battery in the system of the present invention can significantly improve the rate performance and low-temperature performance of the sodium-ion battery by using specific additives in the non-aqueous electrolyte.

[0110] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A sodium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, characterized in that, The negative electrode includes a negative electrode material layer; The non-aqueous electrolyte comprises a sodium salt, a solvent, and additives, wherein the additives include sulfur-containing compounds and silane phosphates, and the silane phosphates are selected from compounds shown in structural formula 1. R1, R2, and R3 are each independently selected from halogen-substituted or unsubstituted C2-C5 alkyl, halogen-substituted or unsubstituted C2-C5 alkenyl, halogen-substituted or unsubstituted C2-C5 alkynyl, or -Si(R4)3. R4 is selected from C2-C5 alkyl, and at least one of R1, R2, and R3 is selected from -Si(R4)3. The sodium-ion battery meets the following conditions: 0.2≤(a+b) / c≤3.5, 0.1≤a≤2, 0.1≤b≤1, 0.85≤c≤1.15; Where: a is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in wt%; b represents the mass percentage of sulfur-containing compounds in the non-aqueous electrolyte, in wt%. c represents the compaction density of the negative electrode material layer, in g / cm³. 3 .

2. The sodium-ion battery according to claim 1, characterized in that, The sodium-ion battery satisfies the following condition: 0.4≤(a+b) / c≤1.

6.

3. The sodium-ion battery according to claim 1, characterized in that, The mass percentage a of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.2 to 1 wt%.

4. The sodium-ion battery according to claim 1, characterized in that, The mass percentage b of sulfur-containing compounds in the non-aqueous electrolyte is 0.2–0.5 wt%.

5. The sodium-ion battery according to claim 1, characterized in that, The compaction density c of the negative electrode material layer is 0.9–1 g / cm³. 3 .

6. The lithium-ion battery according to claim 1, characterized in that, In the compound shown in structural formula 1, R1, R2, and R3 are the same.

7. The sodium-ion battery according to claim 1, characterized in that, The compound represented by structural formula 1 includes one or more of the following compounds:

8. The sodium-ion battery according to claim 1, characterized in that, The sulfur-containing compound includes at least one of cyclic sulfate compounds and sulfonyl lactone compounds; and / or, The cyclic sulfate compounds include at least one of 4-methylvinyl sulfate, vinyl sulfate, and propylene sulfate; and / or, The sulfonyl lactone compounds include at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

9. The sodium-ion battery according to claim 1, characterized in that, The sodium salt includes one or more of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

10. The sodium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte also includes auxiliary additives, which include at least one of cyclic carbonate compounds, borate compounds, and nitrile compounds; and / or, Based on the total mass of the non-aqueous electrolyte (100%), the content of the auxiliary additives is 0.01 wt% to 10 wt%; and / or, The cyclic carbonate compounds include at least one of the following: vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and a compound represented by structural formula 2: In the structural formula 2 shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, C1-C5 group; and / or, The borate ester compounds include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; and / or, The nitrile compounds include at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitol.

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