A sodium-ion battery

Abstract

To overcome the shortcomings of existing sodium-ion batteries in terms of high-rate cycle performance and low-temperature performance, this invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode includes a negative electrode material layer containing a negative electrode active material. The non-aqueous electrolyte comprises a non-aqueous organic solvent and a sodium salt, wherein the sodium salt comprises sodium bis(fluorosulfonyl)imide. The sodium-ion battery satisfies the following conditions: 0.5 ≤ x*y / z ≤ 4.5, and 1.05 ≤ x ≤ 1.20, 2 ≤ y ≤ 12, 1 ≤ z ≤ 12; where x is the N / P ratio of the sodium-ion battery; y is the median particle size of the negative electrode active material in μm; and z is the mass percentage of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte in %. The sodium-ion battery provided by this invention exhibits excellent low-temperature performance, achieving the advantages of high-rate and long-cycle operation.

Description

Technical Field

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

[0002] With the rapid increase in demand for lithium-ion batteries and the continuous rise in lithium resource costs, the production cost of lithium-ion batteries has also gradually increased. Faced with these challenges, researchers have begun to consider using abundant sodium as a substitute for lithium, and have gradually started research on sodium-ion batteries. Sodium-ion batteries are similar in principle and structure to lithium-ion batteries. Compared to lithium batteries, sodium-ion batteries have more abundant resources, lower costs and less price fluctuations, and possess wide temperature range and high safety performance, making them a potential substitute. With the continuous advancement of sodium-ion battery technology, sodium-ion batteries will occupy an important place 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 determining whether they can be industrialized.

[0003] Existing sodium-ion batteries suffer from insufficient high-rate charge-discharge performance. During high-rate charge-discharge, sodium ions are easily deposited unevenly on the negative electrode, forming sodium dendrites, which leads to self-discharge in sodium-ion batteries and affects battery cycle performance. At the same time, the electrolyte viscosity is high at low temperatures, which affects ion conduction performance. Summary of the Invention

[0004] To address the shortcomings of existing sodium-ion batteries in terms of high-rate cycle performance and low-temperature performance, this invention provides a sodium-ion battery.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] This invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode material layer containing a negative electrode active material. The non-aqueous electrolyte comprises a non-aqueous organic solvent and a sodium salt, wherein the sodium salt comprises sodium bis(fluorosulfonyl)imide.

[0007] The sodium-ion battery meets the following conditions:

[0008] 0.5≤x*y / z≤4.5, and 1.05≤x≤1.20, 2≤y≤12, 1≤z≤12;

[0009] Where x is the N / P ratio of the sodium-ion battery;

[0010] y represents the median particle size of the negative electrode active material, in μm;

[0011] z represents the mass percentage of NaFSI in the non-aqueous electrolyte, expressed as %.

[0012] Optionally, the sodium-ion battery satisfies the following conditions:

[0013] 0.8≤x*y / z≤3.2.

[0014] Optionally, the N / P ratio x of the sodium-ion battery is 1.10 to 1.18.

[0015] Optionally, the median particle size y of the negative electrode active material is 4–8 μm.

[0016] Optionally, the mass percentage z of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 2% to 11%.

[0017] Optionally, the negative electrode active material includes at least one of soft carbon, hard carbon, carbon nanotubes, expanded graphite, and graphene.

[0018] Optionally, the positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material includes at least one of a sodium-containing layered oxide, a sodium-containing polyanionic compound, and a sodium-containing Prussian blue compound.

[0019] The sodium-containing layered oxide includes layered transition metal oxides, which include compounds represented by Formula I:

[0020] Na x M y O z Formula I

[0021] Wherein, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V;

[0022] The Prussian blue compound includes the compound represented by Formula II:

[0023] Na x′ L y′ [L′(CN)6] y′ ·z′H2O Formula II

[0024] Wherein, 0 < x′ ≤ 2, 0 < y′ ≤ 1, 0 < z′ ≤ 20, and L and L′ are each selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V;

[0025] The polyanionic compound includes at least one of phosphate compounds and sulfate compounds;

[0026] The phosphate compounds include at least one of the compounds represented by Formula III or Formula IV:

[0027] Na3(M′O 1-qPO4)2F 1+2q Formula III

[0028] Where 0≤q≤1, M′ is selected from at least one of Al, V, Ge, Fe, and Ga:

[0029] Na2EPO4F type IV

[0030] Wherein, E is selected from at least one of Fe and Mn;

[0031] The sulfate compounds include at least one of the compounds represented by Formula V:

[0032] Na2Y(SO4)2·2H2O (Formula V)

[0033] Wherein, Y is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0034] Optionally, the sodium salt further includes an auxiliary sodium salt, which includes at least one of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium bis(oxalate)borate, sodium difluorooxalateborate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0035] Based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the auxiliary sodium salt is 1% to 14%.

[0036] Optionally, the non-aqueous electrolyte further includes additives, which include at least one of vinyl sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, fluorovinyl carbonate, and difluorovinyl carbonate.

[0037] Based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the additive is 1% to 3%.

[0038] Optionally, the non-aqueous organic solvent includes at least one of carbonates, carboxylic acid esters, and ethers;

[0039] Preferably, the carbonates include cyclic or chain carbonates with 3 to 5 carbon atoms, wherein the cyclic carbonates include at least one of ethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; and the chain carbonates include at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0040] The carboxylic acid esters include carboxylic acid esters with 2 to 6 carbon atoms, and the carboxylic acid esters include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate.

[0041] The ethers include cyclic or chain ethers having 4 to 10 carbon atoms; the cyclic ethers include at least one of 1,3-dioxolane, 1,4-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ethers include at least one of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether.

[0042] Based on the mass of the electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 70% to 92%.

[0043] According to the sodium-ion battery provided by the present invention, sodium bis(fluorosulfonyl)imide (NaFSI) is added to the non-aqueous electrolyte. NaFSI can participate in the formation of a passivation film on the negative electrode surface. The passivation film on the negative electrode surface helps to suppress the occurrence of side reactions between the non-aqueous electrolyte and the negative electrode, effectively improves the stability of the non-aqueous electrolyte, and reduces battery impedance. More importantly, the inventors have found through extensive research that when the N / P ratio x of the sodium-ion battery, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte meet the following conditions: When 0.5≤x*y / z≤4.5, and 1.05≤x≤1.20, 2≤y≤12, and 1≤z≤12, the resulting battery system exhibits a fast ion transport rate, and the non-aqueous electrolyte possesses high conductivity and low viscosity. Full-cell testing revealed that, on the one hand, this battery system can achieve high-rate discharge above 10C while suppressing sodium deposition; on the other hand, it is beneficial for improving the quality of the passivation film on the negative electrode surface. The non-aqueous electrolyte has low viscosity at low temperatures, resulting in excellent low-temperature performance of the battery and achieving the performance advantages of high-rate and long-cycle operation. Detailed Implementation

[0044] 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.

[0045] This invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode comprises a negative electrode material layer containing a negative electrode active material. The non-aqueous electrolyte comprises a non-aqueous organic solvent and a sodium salt, wherein the sodium salt comprises sodium bis(fluorosulfonyl)imide.

[0046] The sodium-ion battery meets the following conditions:

[0047] 0.5≤x*y / z≤4.5, and 1.05≤x≤1.20, 2≤y≤12, 1≤z≤12;

[0048] Where x is the N / P ratio of the sodium-ion battery;

[0049] y represents the median particle size of the negative electrode active material, in μm;

[0050] z represents the mass percentage of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte, expressed as %.

[0051] Sodium bis(fluorosulfonyl)imide (NaFSI) is added to the non-aqueous electrolyte. NaFSI can participate in the formation of a passivation film on the negative electrode surface. The passivation film on the negative electrode surface helps to suppress the occurrence of side reactions between the non-aqueous electrolyte and the negative electrode, effectively improving the stability of the non-aqueous electrolyte and reducing battery impedance. More importantly, the inventors have found through extensive research that when the N / P ratio x of the sodium-ion battery, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte meet the condition: 0.5 ≤ x * y When z ≤ 4.5, and 1.05 ≤ x ≤ 1.20, 2 ≤ y ≤ 12, and 1 ≤ z ≤ 12, the resulting battery system exhibits a fast ion transport rate, and the non-aqueous electrolyte possesses high conductivity and low viscosity. Full-cell testing revealed that, on the one hand, this battery system can achieve high-rate discharge above 10C while suppressing sodium deposition; on the other hand, it is beneficial for improving the passivation film quality on the negative electrode surface. The non-aqueous electrolyte has low viscosity at low temperatures, resulting in excellent low-temperature performance of the battery and achieving the performance advantages of high-rate and long-cycle operation.

[0052] In a preferred embodiment, the sodium-ion battery satisfies the following conditions:

[0053] 0.8≤x*y / z≤3.2.

[0054] By further limiting the N / P ratio x of the sodium-ion battery, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte to meet the above conditions, the high-rate discharge performance and low-temperature capacity retention of the sodium-ion battery can be improved.

[0055] In some embodiments, the N / P ratio x of the sodium-ion battery is 1.05, 1.06, 1.08, 1.09, 1.10, 1.13, 1.12, 1.15, 1.17, 1.18, 1.19 or 1.20.

[0056] In a preferred embodiment, the N / P ratio x of the sodium-ion battery is 1.10 to 1.18.

[0057] In sodium-ion battery design, the ratio of the capacity provided by the negative electrode to the capacity provided by the positive electrode is called the N / P ratio. N / P ratio = (specific capacity of negative electrode active material × areal density of negative electrode × content of negative electrode active material) / (specific capacity of positive electrode active material × areal density of positive electrode × content of positive electrode active material). When the N / P ratio of a sodium-ion battery is within the above range, it effectively ensures the battery's capacity utilization, suppresses sodium deposition caused by fast charging and discharging, and provides better rate discharge and safety performance. If the N / P ratio is too small, the positive electrode active material in the positive electrode cannot be fully utilized, resulting in insufficient capacity release and excessive sodium ion deposition on the negative electrode surface, leading to severe sodium deposition and deterioration of battery performance. This results in reduced capacity retention and significantly worse rate performance. Conversely, if the N / P ratio is too large, the proportion of positive electrode active material in the positive electrode is low, while the negative electrode capacity is too large, leading to a decrease in the material's energy density, resulting in reduced capacity retention and significantly worse rate performance.

[0058] In some embodiments, the median particle size y of the negative electrode active material can be 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 7.8 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 11 μm, or 12 μm.

[0059] In a preferred embodiment, the median particle size y of the negative electrode active material is 4–8 μm.

[0060] When the median particle size y of the negative electrode active material is within the above-mentioned range, it is beneficial to reduce the excessive decomposition of the electrolyte in film formation while taking into account the ion transport rate. This can improve the first charge and discharge efficiency of the battery while ensuring good rate performance. If the particle size of the negative electrode active material is too small, the electrolyte will participate excessively in film formation, increasing the irreversible capacity and reducing the battery capacity retention rate. At the same time, it will make the internal structure of the negative electrode material layer too dense, affecting the wetting of the non-aqueous electrolyte in the negative electrode material layer and hindering the diffusion of sodium ions. On the other hand, if the particle size of the negative electrode material is too large, the transport time of sodium ions in the negative electrode material particles will increase, which will also reduce the transport rate of sodium ions in the negative electrode, worsen the rate performance of the battery, and reduce the battery capacity retention rate.

[0061] In some embodiments, the mass percentage z of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte can be 1%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, or 12%.

[0062] In a preferred embodiment, the mass percentage z of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 2% to 11%.

[0063] When the mass percentage z of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is within the above-mentioned range, it can improve the conductivity and electrochemical stability of the non-aqueous electrolyte, while participating in the formation of the passivation film, inhibiting the occurrence of side reactions between the electrolyte and the electrode, effectively reducing the impedance during battery cycling, and improving cycle performance. If the content of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is too low, the conductivity of the non-aqueous electrolyte is too low, and it cannot effectively participate in the formation of the passivation film on the negative electrode surface, resulting in little improvement in battery performance. When too much sodium bis(fluorosulfonyl)imide is added, the viscosity of the non-aqueous electrolyte increases, which seriously degrades the low-temperature performance of the battery, resulting in a decrease in battery capacity retention and a significant deterioration in rate performance.

[0064] In some embodiments, the negative electrode active material includes at least one of soft carbon, hard carbon, carbon nanotubes, expanded graphite, and graphene.

[0065] In some embodiments, the positive electrode includes a positive electrode material layer containing a positive electrode active material, wherein the positive electrode active material includes at least one of a sodium-containing layered oxide, a sodium-containing polyanionic compound, and a sodium-containing Prussian blue compound.

[0066] The sodium-containing layered oxide includes layered transition metal oxides, which include compounds represented by Formula I:

[0067] Na x M y O z Formula I

[0068] Wherein, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V;

[0069] The Prussian blue compound includes the compound represented by Formula II:

[0070] Na x′ L y′ [L′(CN)6] y′·z′H2O Formula II

[0071] Wherein, 0 < x′ ≤ 2, 0 < y′ ≤ 1, 0 < z′ ≤ 20, and L and L′ are each selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V;

[0072] The polyanionic compound includes at least one of phosphate compounds and sulfate compounds;

[0073] The phosphate compounds include at least one of the compounds represented by Formula III or Formula IV:

[0074] Na3(M′O 1-q PO4)2F 1+2q Formula III

[0075] Where 0≤q≤1, M′ is selected from at least one of Al, V, Ge, Fe, and Ga:

[0076] Na2EPO4F type IV

[0077] Wherein, E is selected from at least one of Fe and Mn;

[0078] The sulfate compounds include at least one of the compounds represented by Formula V;

[0079] Na2Y(SO4)2·2H2O (Formula V)

[0080] Wherein, Y is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0081] In some preferred embodiments, the layered transition metal oxide includes NaNi. m Fe n Mn p O2 compounds, NaNi m Co n Mn p At least one of the O2 compounds, wherein m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1;

[0082] The Prussian blue compound includes Na. x′ Mn[Fe(CN)6] y′ ·z′H2O compounds, Na x′ Fe[Fe(CN)6] y′ At least one of the compounds z′H2O, wherein 0<x′≤2, 0<y′≤1, and 0<z′≤20;

[0083] The phosphate compounds include at least one of Na3(VPO4)2F3, Na3(VOPO4)2F, Na2FePO4F, and Na2MnPO4F.

[0084] In some embodiments, the sodium salt further includes an auxiliary sodium salt, which includes at least one of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium bis(oxalateborate)borate (NaBOB), sodium difluorooxalateborate (NaODFB), sodium hexafluoroarsenate (NaAsF6), sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0085] Based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the auxiliary sodium salt is 1% to 14%.

[0086] By using the aforementioned auxiliary sodium salt, it is beneficial to suppress the corrosive effect of non-aqueous electrolyte on the positive and negative current collectors.

[0087] In some embodiments, the non-aqueous electrolyte further includes additives, the additives including at least one of vinyl sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, fluoroethylene carbonate, and difluoroethylene carbonate.

[0088] Based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the additive is 1% to 3%.

[0089] In some embodiments, the non-aqueous organic solvent includes at least one of carbonates, carboxylic acid esters, and ethers;

[0090] Preferably, the carbonates include cyclic or chain carbonates with 3 to 5 carbon atoms, wherein the cyclic carbonates include at least one of ethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; and the chain carbonates include at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0091] The carboxylic acid esters include carboxylic acid esters with 2 to 6 carbon atoms, and the carboxylic acid esters include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate.

[0092] The ethers include cyclic or chain ethers having 4 to 10 carbon atoms; the cyclic ethers include at least one of 1,3-dioxolane, 1,4-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ethers include at least one of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether.

[0093] Based on the mass of the electrolyte being 100%, the mass percentage of the non-aqueous organic solvent is 70% to 92%.

[0094] The present invention will be further illustrated by the following examples.

[0095] Table 1

[0096]

[0097]

[0098] Example 1

[0099] This embodiment illustrates the sodium-ion battery and its preparation method disclosed in this invention, including the following steps:

[0100] 1) Preparation of non-aqueous electrolyte:

[0101] Ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:PC:EMC = 1:2:7. Sodium bis(fluorosulfonyl)imide (NaFSI) and additives were added in the mass percentages shown in Example 1 of Table 1, based on the total weight of the non-aqueous electrolyte as 100%.

[0102] 2) Preparation of the positive electrode:

[0103] The positive electrode active material Na was mixed at a mass ratio of 93:4:3. 1.2 Ni2[Fe(CN)6] 0.5 H2O, conductive carbon black Super-P, and polyvinylidene fluoride (PVDF) binder are dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. Aluminum foil is used as the positive electrode current collector, and the slurry is uniformly coated on both sides of the foil. After drying, calendering, and vacuum drying, a positive electrode material layer is obtained. Aluminum leads are then welded on using an ultrasonic welder to obtain the positive electrode sheet.

[0104] 3) Preparation of the negative electrode:

[0105] The negative electrode active materials hard carbon, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) with median particle sizes as shown in Table 1 were mixed at a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain the negative electrode sheet.

[0106] 4) Cell fabrication:

[0107] A separator is placed between the positive and negative electrodes, and the N / P ratio of the positive and negative electrodes is shown in Table 1. Then, the sandwich structure composed of the positive electrode, negative electrode 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 85°C for 48 hours to obtain the cell to be injected with electrolyte.

[0108] 5) Electrolyte injection and formation of the battery cell:

[0109] 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.

[0110] Then, perform the first-charge routine formation as follows: Charge the sodium-ion battery at a constant current of 0.05C for at least 2 hours, then charge it at a constant current of 0.3C until it reaches 3.5V and stop charging. Then, age the sodium-ion battery at room temperature for 30-60 minutes and vacuum seal it a second time. Continue to charge and form the sodium-ion battery at a rate of 0.3C. Stop charging when the formation potential reaches 3.95V. Then, age the sodium-ion battery at room temperature for a period of time. Continue to charge and form the sodium-ion battery at a rate of 0.3C until it reaches 100% SOC to obtain the sodium-ion battery.

[0111] Examples 2-19

[0112] Examples 2-19 illustrate the sodium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences:

[0113] The sodium salt and its amount, additives and their amounts, median particle size and N / P ratio of the negative electrode active material were used as shown in Examples 2-19 in Table 1.

[0114] Comparative Examples 1-14

[0115] Comparative Examples 1-14 are used to illustrate the sodium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, the difference being:

[0116] The sodium salts and their amounts, additives and their amounts, median particle size and N / P ratio of the negative electrode active material were used as shown in Comparative Examples 1 to 14 in Table 1.

[0117] Performance testing

[0118] The sodium-ion batteries prepared in Examples 1-19 and Comparative Examples 1-14 were subjected to the following performance tests:

[0119] 1. Electrolyte conductivity test at 25℃

[0120] The conductivity of the electrolyte was tested at 25°C using a conductivity meter.

[0121] 2. Low-temperature performance test:

[0122] At 25℃, the formed battery was charged to 3.9V using a constant current of 0.5C, followed by constant voltage charging at 3.9V with a cutoff current of 0.05C. It was then discharged to 1.5V using a constant current of 0.5C, and the discharge capacity was recorded. The battery was then charged to 3.9V using a constant current of 0.5C, followed by constant voltage charging at 3.9V with a cutoff current of 0.05C. After being placed in an environment at -20℃ for 12 hours, it was discharged to 1.5V using a constant current of 0.5C, and the discharge capacity was recorded. The calculation formula is as follows:

[0123] -20℃ discharge capacity retention % = 0.5C discharge capacity (-20℃) / 0.5C discharge capacity (25℃) × 100%

[0124] 3. Cyclic performance test:

[0125] The sodium-ion batteries prepared in the examples and comparative examples were placed at room temperature (25°C) and charged at a constant current of 0.7C to 3.9V, followed by constant voltage charging at 3.9V with a cutoff current of 0.05C, and then discharged at a constant current of 1C to 1.5V. This cycle was repeated for 200 cycles. The capacity retention rate after 200 cycles at 25°C was calculated using the following formula:

[0126] Capacity retention rate after 200 cycles at 25℃ = discharge capacity in the 200th cycle / discharge capacity in the 1st cycle × 100%.

[0127] 4. High-temperature cycling performance test:

[0128] The sodium-ion batteries prepared in the examples and comparative examples were subjected to a high temperature of 45°C, charged at a constant current of 0.7C to 3.9V, then charged at a constant voltage of 3.9V with a cutoff current of 0.05C, and then discharged at a constant current of 1C to 1.5V. This cycle was repeated for 200 cycles. The capacity retention rate after 200 cycles at 45°C was calculated using the following formula:

[0129] Capacity retention rate after 200 cycles at 45℃ = discharge capacity in the 200th cycle / discharge capacity in the 1st cycle × 100%.

[0130] 5. Ratio Performance Test:

[0131] At 25°C, the formed battery was charged to 3.9V using a constant current of 0.5C, followed by constant voltage charging at 3.9V with a cutoff current of 0.05C. It was then discharged to 1.5V using a constant current of 0.5C, and the discharge capacity was recorded. The battery was then charged again to 3.9V using a constant current of 0.5C, followed by constant voltage charging at 3.9V with a cutoff current of 0.05C, and then discharged to 1.5V using a constant current of 10C, and the discharge capacity was recorded. The 10C rate discharge capacity ratio was calculated using the following formula:

[0132] 10C rate discharge capacity ratio % = (0.5C discharge capacity / 10C discharge capacity) × 100%

[0133] 6. Sodium precipitation phenomenon test:

[0134] The sodium-ion batteries prepared in the examples and comparative examples were placed at room temperature of 25°C and charged at a constant current of 0.7C to 3.9V. Then, they were charged at a constant voltage of 3.9V with a cutoff current of 0.05C. Then, they were discharged at a constant current of 10C to 1.5V. This cycle was repeated for 50 cycles. The batteries were then disassembled, and the negative electrode was removed to observe whether sodium deposition occurred.

[0135] (1) The test results obtained from Examples 1-16 and Comparative Examples 1-14 are filled in Table 2.

[0136] Table 2

[0137]

[0138]

[0139] The test results from Examples 1-16 and Comparative Examples 1-14 show that the N / P ratio x of the sodium-ion battery, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte have a significant correlation with maintaining the stability of the non-aqueous electrolyte and improving the performance of the sodium-ion battery. When the N / P ratio x of the sodium-ion battery, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte satisfy the following relationship: 0.5≤x*y / z≤4.5, and 1.05≤x≤1.20, 2≤y≤12, 1≤z≤12, the obtained sodium-ion battery has a better low-temperature and high-temperature discharge capacity retention rate, meets the high-rate discharge requirement of 10C or above, and does not have the problem of sodium deposition. It is speculated that NaFSI participates in the formation of the passivation film on the negative electrode surface. By adjusting the N / P ratio of the sodium-ion battery and the median particle size of the negative electrode active material, the contact area and concentration between NaFSI and the negative electrode surface, as well as the penetration of the non-aqueous electrolyte into the interior of the negative electrode material layer, can be adjusted. Ultimately, this affects the stability and density of the passivation film formed by NaFSI, keeping it at a relatively thin level. This reduces the interfacial ion conduction resistance between the negative electrode and the non-aqueous electrolyte, which is beneficial for improving the performance of sodium-ion batteries under low temperature and high-rate discharge conditions. At the same time, it densifies the passivation film, making it more stable, thereby avoiding the occurrence of side reactions of the non-aqueous electrolyte under high temperature conditions and improving the high-temperature cycle performance of sodium-ion batteries.

[0140] As can be seen from the test results of Examples 1-16, when the N / P ratio x of the sodium-ion battery, the median particle size y of the negative electrode active material, and the mass percentage of NaFSI in the non-aqueous electrolyte z further satisfy the conditions 0.8≤x*y / z≤3.2, and 1.10≤x≤1.18, 4≤y≤8, 2≤z≤11, the sodium-ion battery has the best comprehensive performance.

[0141] The test results from Comparative Examples 1 to 7 show that when any of the parameters x, y, and z exceeds the limit, even if the requirement of the relationship 0.5 ≤ x*y / z ≤ 4.5 is met, the capacity retention rate of sodium-ion batteries under high temperature conditions, low temperature conditions, and high-rate discharge are still poor. This indicates that when the N / P ratio x, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte are too high or too low, they will affect the formation of the passivation film on the negative electrode surface and the stability of the non-aqueous electrolyte under rapid discharge conditions. In some cases, it may even lead to sodium deposition. The test results from Comparative Examples 8 to 14 show that even if the x, y, and z values ​​all meet their parameter range limits, excessively large or small x*y / z values ​​will lead to the deterioration of the battery's high and low temperature performance and fast discharge performance. This indicates that there is an interaction between the N / P ratio x of sodium-ion batteries, the median particle size y of the negative electrode active material, and the mass percentage z of NaFSI in the non-aqueous electrolyte. Only when the three reach a good balance can they significantly improve the high and low temperature performance and fast discharge performance of sodium-ion batteries.

[0142] (2) The test results obtained in Examples 1, 17-19 are filled in Table 3.

[0143] Table 3

[0144]

[0145] As can be seen from the test results of Examples 1 and 17-19, based on the battery system provided by the present invention, replacing the additive FEC with DTD (ethylene sulfate), 1,3-PS (1,3-propane sulfonyl lactone), and RPS (1,3-propene sulfonyl lactone) can still ensure that the high and low temperature performance and high-rate discharge performance of the sodium-ion battery are at a relatively good level. This indicates that the battery system provided by the present invention has a good synergistic effect with DTD (ethylene sulfate), 1,3-PS (1,3-propane sulfonyl lactone), RPS (1,3-propene sulfonyl lactone), and FEC (fluoroethylene carbonate). It can be seen that in the sodium-ion battery system provided by the present invention, when FEC (fluoroethylene carbonate) is used as an additive, it has the best improvement effect on the high and low temperature performance and high-rate discharge performance of the sodium-ion battery.

[0146] The above description is only 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 sodium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the negative electrode comprises a negative electrode material layer containing a negative electrode active material, the non-aqueous electrolyte comprises a non-aqueous organic solvent and a sodium salt, and the sodium salt comprises sodium bis(fluorosulfonyl)imide; The sodium ion battery satisfies the following conditions: 0.5≤x*y / z≤4.5, and 1.05≤x≤1.20, 2≤y≤12, and 1≤z≤12; wherein x is the N / P ratio of the sodium ion battery; y is the median particle size of the negative electrode active material, in μm; z is the mass percentage of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte, in %.

2. The sodium-ion battery of claim 1, wherein, The sodium ion battery satisfies the following conditions: 0.8≤x*y / z≤3.

2.

3. The sodium-ion battery of claim 1, wherein, The N / P ratio x of the sodium ion battery is 1.10-1.

18.

4. The sodium-ion battery of claim 1, wherein, The median particle size y of the negative electrode active material is 4-8 μm.

5. The sodium-ion battery of claim 1, wherein, The mass percentage z of sodium bis(fluorosulfonyl)imide in the non-aqueous electrolyte is 2%-11%.

6. The sodium-ion battery of claim 1, wherein, The negative electrode active material comprises at least one of soft carbon, hard carbon, carbon nanotube, expanded graphite and graphene.

7. The sodium-ion battery of claim 1, wherein, The positive electrode comprises a positive electrode material layer containing a positive electrode active material, and the positive electrode active material comprises at least one of sodium-containing layered oxide, sodium-containing polyanion compound and sodium-containing Prussian blue compound.

8. The sodium-ion battery of claim 7, wherein, The sodium-containing layered oxide comprises layered transition metal oxide, and the layered transition metal oxide comprises a compound represented by Formula I: Na x M y O z Formula I wherein 0 The Prussian blue compound comprises a compound represented by Formula II: Na x´ L y´ [L´(CN)6] y´ •z´H2O Formula II wherein 0 The polyanion compound comprises at least one of phosphate compound and sulfate compound. The phosphate compound comprises at least one of a compound represented by Formula III or Formula IV: Na3(M'0 1-q PO4)2F 1+2q Formula III wherein 0 Na2EPO4F Formula IV wherein E is at least one of Fe and Mn; The sulfate compound comprises at least one of a compound represented by Formula V: Na2Y(SO4)2•2H2O Formula V wherein Y is at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb and V.

9. The sodium-ion battery of claim 1, wherein, The sodium salt further comprises an auxiliary sodium salt, and the auxiliary sodium salt comprises at least one of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium bis(oxalate)borate, sodium difluoro(oxalate)borate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethylsulfonate and sodium bis(trifluoromethylsulfonyl)imide. The mass percentage of the auxiliary sodium salt is 1%-14% based on the total mass of the non-aqueous electrolyte.

10. The sodium-ion battery of claim 1, wherein, The non-aqueous electrolyte further comprises an additive, the additive comprising at least one of vinyl sulfate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, fluoroethylene carbonate and bisfluoroethylene carbonate; The mass percentage of the additive is 1% to 3% based on the total mass of the non-aqueous electrolyte.

11. The sodium-ion battery of claim 1, wherein, The non-aqueous organic solvent comprises at least one of carbonates, carboxylic acid esters and ethers.

12. The sodium-ion battery of claim 11, wherein, The carbonates comprise cyclic or chain carbonates with carbon atom number 3 to 5, the cyclic carbonates comprising at least one of vinyl carbonate, vinylene carbonate, vinyl ethylene carbonate, propylene carbonate, gamma-butyrolactone and butylene carbonate; the chain carbonates comprising at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and dipropyl carbonate; The carboxylic acid esters comprise carboxylic acid esters with carbon atom number 2 to 6, the carboxylic acid esters comprising at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate and propyl propionate; The ethers comprise cyclic or chain ethers with carbon atom number 4 to 10, the cyclic ethers comprising at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, 2-methyl tetrahydrofuran and 2-trifluoromethyl tetrahydrofuran; the chain ethers comprising at least one of dimethoxymethane, 1,2-dimethoxyethane and diglyme; The mass percentage of the non-aqueous organic solvent is 70% to 92% based on the mass of the electrolyte.

Images