Sodium-ion battery negative electrode sheet, sodium-ion battery and application

Abstract

This invention discloses a sodium-ion battery negative electrode sheet, a sodium-ion battery, and its applications. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material coating applied to the current collector. The active material coating in the negative electrode sheet features a low loading, meaning the amount of negative electrode active material used is significantly lower than that in conventional batteries. The sodium-ion battery negative electrode sheet disclosed in this application can significantly improve the energy density of sodium-ion batteries and reduce their cost while providing the same energy. This application also provides a sodium-ion battery containing this negative electrode sheet, which uses a specially formulated electrolyte to suppress the formation of sodium dendrites under the low loading negative electrode active material design, thus improving the battery's cycle performance and safety performance.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, specifically to sodium-ion battery negative electrode sheets, sodium-ion batteries, and their applications. Background Technology

[0002] Energy storage technology is key to the large-scale application of renewable energy and new energy vehicles, and lithium-ion batteries are widely used as energy storage devices. However, lithium resources, as a core supporting element, are scarce in the earth's crust, leading to high battery costs.

[0003] Sodium-ion batteries have attracted increasing attention due to their abundant resources, sustainable development, and low cost. However, the technology of sodium-ion battery electrode materials is immature, sodium ions have a large radius, resulting in high resistance during insertion / extraction in the electrode material, and a low charge / discharge voltage plateau, ultimately leading to a lower energy density compared to lithium-ion batteries. To improve the energy density of sodium-ion batteries, new high-energy-density electrode materials can be developed, the actual proportion of electrode materials can be reduced, and anode-free battery systems can be used. However, anode-free battery systems face challenges such as the reaction of sodium metal with the electrolyte on the anode surface and sodium dendrite formation due to the low deposition potential of sodium, making commercial applications of sodium-ion batteries difficult. Summary of the Invention

[0004] This invention addresses the above-mentioned problems by proposing a sodium-ion battery negative electrode sheet, a sodium-ion battery, and its applications, which can effectively improve the energy density of sodium-ion batteries and suppress the formation of sodium dendrites. Furthermore, the cycle performance of the battery is also significantly improved.

[0005] One of the objectives of this invention is to provide a negative electrode for sodium-ion batteries, thereby solving the problems of low energy density and high cost of current sodium-ion batteries.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A sodium-ion battery negative electrode sheet includes a negative electrode current collector and a negative electrode active material coating applied to the negative electrode current collector. The negative electrode active material coating includes a carbon material and a polymer binder. The active material coating in the negative electrode sheet exhibits a low loading capacity, meaning the amount of negative electrode active material used is significantly lower than that used in conventional batteries, and satisfies the following formula:

[0008] 0.1≤Ac*Aw / Qd*Qw≤0.8

[0009] Where Ac is the initial charge specific capacity of the negative electrode active material (mAh / g), and Aw is the coating amount of the negative electrode active material (g / cm³). 2 Qc is the initial discharge specific capacity of the positive electrode active material (mAh / g), and Qw is the coating amount of the positive electrode active material (g / cm³).2 Preferably, the coating amount of the electrode active material satisfies 0.1≤Ac*Aw / Qd*Qw≤0.6; more preferably, the coating amount of the electrode active material satisfies 0.1≤Ac*Aw / Qd*Qw≤0.3.

[0010] The carbon material includes one or more of hard carbon, graphite, modified graphite, fluorinated graphite, activated carbon, porous carbon, carbon fiber, carbon nanotubes, graphene, and soft carbon. The carbon material constitutes 90% to 98% of the negative electrode active material coating by mass, preferably 95%.

[0011] The specific surface area of ​​the negative electrode active material is ≥2m². 2 / g, preferably with a specific surface area of ​​4m³ 2 / g、8m 2 / g or 10m 2 / g.

[0012] The negative electrode current collector includes one of aluminum foil, copper foil, foamed nickel foil, metal mesh current collector, carbon paper current collector, stainless steel current collector, carbon cloth current collector, and metal polymer composite current collector.

[0013] The polymer binder is one or more of the following: polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, styrene-butadiene rubber, sodium alginate, polyaniline, polypyrrole, sodium carboxymethyl cellulose, and butadiene acrylate rubber.

[0014] Furthermore, the negative electrode sheet designed with low loading negative electrode active material can lead to the formation of sodium dendrites. The second objective of this invention is to provide a sodium-ion battery that increases the growth barrier of sodium dendrites, inhibits the formation of sodium dendrites, and improves the cycle performance of sodium-ion batteries.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] The sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that the negative electrode is the same as the negative electrode described in the first purpose.

[0017] The electrolyte comprises an organic solvent, additives, and a sodium salt. The organic solvent comprises at least 40% chain carbonate solvent and at least 10% and less than or equal to 60% ether solvent; preferably, the chain carbonate solvent comprises at least 50% and the ether solvent comprises at least 20% and less than or equal to 50%. The chain carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; the ether solvent includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether; other organic solvents include cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, and butylene carbonate, as well as one or more of acetonitrile, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, and methyl ethyl phosphate.

[0018] The sodium salt includes one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium difluorosulfonamide, sodium trifluoromethanesulfonate, sodium perchlorate, and sodium ditrifluoromethanesulfonamide.

[0019] The additive is a certain amount of rubidium salt or cesium salt. The rubidium salt or cesium salt is one or more of its corresponding hexafluorophosphate, tetrafluoroborate, bis(fluorosulfonyl)imide salt, trifluoromethanesulfonate, perchlorate, and bis(trifluoromethanesulfonyl)imide salt. The amount of rubidium salt or cesium salt added is 0.01% to 0.1% (by mass of the electrolyte).

[0020] The positive electrode sheet includes a positive current collector and a positive active material coating applied to the surface of the positive current collector. The positive active material coating includes a positive active material, a binder, and a conductive agent. The positive active material includes one or more of transition metal oxide positive electrode materials, polyanionic compounds, and Prussian blue compounds.

[0021] The separator is one or more of the following: polyethylene film, polypropylene film, polyethylene / propylene composite film, glass fiber film, and polyimide film.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The negative electrode sheet, sodium-ion battery and their applications provided by this invention have a lower loading of negative active material compared to that in traditional batteries, which can significantly improve the energy density of sodium-ion batteries. In addition, the cost of sodium-ion batteries is reduced while providing the same energy.

[0024] (2) Due to the use of a specially formulated electrolyte, the low-load negative electrode sheet will inhibit the growth of sodium dendrites during the charging process. On the other hand, during the first charge cycle, sodium metal will preferentially deposit in the micropores or microcrystals of the negative electrode active material. When the micropores or microcrystals are filled with sodium metal, sodium metal will continue to deposit on its surface to form a nanoscale sodium metal layer. Under the synergistic inhibition effect of the electrolyte, the sodium metal deposited on the surface afterward has a very small overpotential, which reduces the formation of sodium dendrites and is beneficial to improving the cycle performance and safety performance of the battery.

[0025] (3) The sodium-ion battery negative electrode sheet and sodium-ion battery of the present invention are green, safe and low-cost energy storage devices that can be used in distributed energy storage, low-speed electric vehicles, two-wheeled electric vehicles, 5G base stations, outdoor emergency power supplies, large-scale energy storage and new energy vehicles, and have great cost, safety and performance advantages. Detailed Implementation

[0026] To further illustrate the technical solutions and advantages of the present invention, the present invention is described with reference to the following specific embodiments, but the present invention is not limited to these examples.

[0027] Example 1

[0028] Layered oxide NaFe 0.3 Ni 0.3 Mn 0.3 Ti 0.05 Mg 0.05 O2 is used as the positive electrode active material. The positive electrode sheet is manufactured as follows: According to the positive electrode active material (NaFe... 0.3 Ni 0.3 Mn 0.3 Ti 0.05 Mg 0.05 O2): Conductive agent (Super P): Binder (polyvinylidene fluoride PVDF) are mixed in a ratio of 95:3:2 to form a slurry. The slurry is then coated onto the surface of aluminum foil using a coating machine according to unit area mass and dried. The coated electrode is then rolled using a roller press to prepare the positive electrode. Hard carbon is used as the negative electrode active material (specific surface area 3.5 m²). 2The negative electrode is prepared as follows: A slurry is prepared by mixing negative electrode active material (hard carbon): binder 1 (CMC): binder 2 (styrene-butadiene rubber SBR) in a ratio of 95:3:2. The slurry is coated onto the surface of aluminum foil using a coating machine according to unit area mass and then dried. The coated electrode is then rolled using a roller press to obtain the negative electrode. The negative electrode capacity per unit area is 0.1 ppm compared to the positive electrode capacity. An electrolyte is prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% of the electrolyte mass) as an additive. The proportion of chain carbonate solvent is 40%, and the proportion of ethylene glycol dimethyl ether is 20%. Battery assembly: A sodium-ion coin cell is assembled using polypropylene as the battery separator. At room temperature, after 100 cycles at a 1C current density, the capacity retention is 90%, with an initial coulombic efficiency of 90%.

[0029] Example 2

[0030] Unlike Example 1, the negative electrode capacity per unit area was 0.5 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, diethyl carbonate, methyl ethyl carbonate, and diethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.1% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 60%, and the proportion of diethylene glycol dimethyl ether was 30%. Battery assembly: A sodium-ion coin cell was assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 91%, with an initial coulombic efficiency of 90%.

[0031] The rest is the same as in Example 1, and will not be repeated here.

[0032] Example 3

[0033] Unlike Example 1, the negative electrode capacity per unit area was 0.8 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 80%, and the proportion of ethylene glycol dimethyl ether was 10%. Battery assembly: Sodium-ion coin cells were assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 89%, with an initial coulombic efficiency of 91%.

[0034] The rest is the same as in Example 1, and will not be repeated here.

[0035] Example 4

[0036] Unlike Example 1, the negative electrode capacity per unit area was 0.2 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and triethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (0.6M), and cesium hexafluorophosphate (0.1% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 50%, and the proportion of triethylene glycol dimethyl ether was 20%. Battery assembly: Sodium-ion coin cells were assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 93%, with an initial coulombic efficiency of 90%.

[0037] The rest is the same as in Example 1, and will not be repeated here.

[0038] Example 5

[0039] Unlike Example 1, the negative electrode capacity per unit area was 0.4 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 50%, and the proportion of ethylene glycol dimethyl ether was 40%. Battery assembly: Sodium-ion coin cells were assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 89%, with an initial coulombic efficiency of 88%.

[0040] The rest is the same as in Example 1, and will not be repeated here.

[0041] Example 6

[0042] Using Na2FeP2O7 / C as the positive electrode active material, the positive electrode sheet is fabricated as follows: A slurry is prepared by mixing the positive electrode active material (Na2FeP2O7 / C): conductive agent (Super P): binder (polyvinylidene fluoride PVDF) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine at a unit area mass ratio and dried. The coated electrode sheet is then rolled using a roller press to obtain the positive electrode sheet. Hard carbon is used as the negative electrode active material (specific surface area 3.5 m²). 2The negative electrode sheet is prepared as follows: A slurry is prepared by mixing the negative electrode active material (hard carbon), binder 1 (CMC), and binder 2 (styrene-butadiene rubber SBR) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine and dried. The coated electrode sheet is then rolled using a roller press to obtain the negative electrode sheet. The negative electrode capacity per unit area is 0.2 ppm, while the positive electrode capacity is 0.2 ppm. An electrolyte is prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and dimethyl glycol ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of chain carbonate solvent is 50%, and the proportion of dimethyl glycol ether is 40%. Battery assembly: A sodium-ion coin cell is assembled using polypropylene as the battery separator. At room temperature, after 100 cycles at a 1C current density, the capacity retention rate is 87%, with an initial coulombic efficiency of 89%.

[0043] Example 7

[0044] Using Na2FeP2O7 / C as the positive electrode active material, the positive electrode sheet is fabricated as follows: A slurry is prepared by mixing the positive electrode active material (Na2FeP2O7 / C): conductive agent (Super P): binder (polyvinylidene fluoride PVDF) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine at a unit area mass ratio and dried. The coated electrode sheet is then rolled using a roller press to obtain the positive electrode sheet. Soft carbon is used as the negative electrode active material (specific surface area 5.6 m²). 2 The negative electrode sheet is prepared as follows: A slurry is prepared by mixing the negative electrode active material (soft carbon), binder 1 (CMC), and binder 2 (styrene-butadiene rubber SBR) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine and dried. The coated electrode sheet is then rolled using a roller press to obtain the negative electrode sheet. The negative electrode capacity per unit area is 0.2 ppm compared to the positive electrode capacity. An electrolyte is prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% of the electrolyte mass) as an additive. The proportion of chain carbonate solvent is 50%, and the proportion of diethylene glycol dimethyl ether is 40%. Battery assembly: A sodium-ion coin cell is assembled using polypropylene as the battery separator. At room temperature, after 100 cycles at a 1C current density, the capacity retention is 89%, with an initial coulombic efficiency of 90%.

[0045] Example 8

[0046] Unlike Example 7, the negative electrode capacity per unit area was 0.6 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, diethyl carbonate, methyl ethyl carbonate, and diethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 50%, and the proportion of diethylene glycol dimethyl ether was 40%. Battery assembly: Sodium-ion coin cells were assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 90%, with an initial coulombic efficiency of 86%.

[0047] The rest is the same as in Example 7, and will not be repeated here.

[0048] Example 9

[0049] Using Na2FePO4F / C as the positive electrode active material, the positive electrode sheet is fabricated as follows: A slurry is prepared by mixing the positive electrode active material (Na2FePO4F / C): conductive agent (Super P): binder (polyvinylidene fluoride PVDF) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine at a unit area mass ratio and dried. The coated electrode sheet is then rolled using a roller press to obtain the positive electrode sheet. Soft carbon is used as the negative electrode active material (specific surface area 5.6 m²). 2 The negative electrode sheet is prepared as follows: A slurry is prepared by mixing negative electrode active material (soft carbon): binder 1 (CMC): binder 2 (styrene-butadiene rubber SBR) in a ratio of 95:3:2. The slurry is coated onto the surface of aluminum foil using a coating machine according to unit area mass and then dried. The coated electrode sheet is then rolled using a roller press to obtain the negative electrode sheet. The negative electrode capacity per unit area is 0.6 ppm compared to the positive electrode capacity. An electrolyte is prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% of the electrolyte mass) as an additive. The chain solvent ratio is 50%, and the ethylene glycol dimethyl ether ratio is 40%. Battery assembly: A sodium-ion coin cell is assembled using polypropylene as the battery separator. At room temperature, after 100 cycles at a 1C current density, the capacity retention rate is 86%, with an initial coulombic efficiency of 89%.

[0050] Example 10

[0051] Using Na2FePO4F / C as the positive electrode active material, the positive electrode sheet is fabricated as follows: A slurry is prepared by mixing the positive electrode active material (Na2FePO4F / C): conductive agent (Super P): binder (polyvinylidene fluoride PVDF) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine at a unit area mass ratio and dried. The coated electrode sheet is then rolled using a roller press to obtain the positive electrode sheet. Hard carbon is used as the negative electrode active material (specific surface area 3.5 m²). 2 The negative electrode is prepared as follows: A slurry is prepared by mixing the negative electrode active material (hard carbon), binder 1 (CMC), and binder 2 (styrene-butadiene rubber SBR) in a ratio of 95:3:2. The slurry is then coated onto the surface of aluminum foil using a coating machine and dried. The coated electrode is then rolled using a roller press to obtain the negative electrode. The negative electrode capacity per unit area is 0.3. An electrolyte is prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% of the electrolyte mass) as an additive. The chain solvent accounts for 50%, and the ethylene glycol dimethyl ether accounts for 40%. Battery assembly: A sodium-ion coin cell is assembled using polypropylene as the battery separator. At room temperature, after 100 cycles at a 1C current density, the capacity retention is 88%, with an initial coulombic efficiency of 87%.

[0052] Comparative Example 1

[0053] Unlike Example 1, the negative electrode capacity per unit area is 1:the positive electrode capacity. An electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 40%, and the proportion of ethylene glycol dimethyl ether was 20%. Battery assembly: A sodium-ion coin cell was assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 95%, with an initial coulombic efficiency of 91%.

[0054] The rest is the same as in Example 1, and will not be repeated here.

[0055] Comparative Example 2

[0056] Unlike Example 1, the negative electrode capacity per unit area was 0.5 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 30%, and the proportion of ethylene glycol dimethyl ether was 20%. Battery assembly: A sodium-ion coin cell was assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 67%, with an initial coulombic efficiency of 73%.

[0057] The rest is the same as in Example 1, and will not be repeated here.

[0058] Comparative Example 3

[0059] Unlike Example 1, the negative electrode capacity per unit area was 0.05 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 50%, and the proportion of ethylene glycol dimethyl ether was 40%. Battery assembly: A sodium-ion coin cell was assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 55%, with an initial coulombic efficiency of 65%.

[0060] The rest is the same as in Example 1, and will not be repeated here.

[0061] Comparative Example 4

[0062] Unlike Example 1, the negative electrode capacity per unit area was 0.5 times that of the positive electrode. The electrolyte was prepared using propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and ethylene glycol dimethyl ether as solvents, sodium hexafluorophosphate as the sodium salt (1M), and cesium hexafluorophosphate (0.02% by mass of the electrolyte) as an additive. The proportion of the chain carbonate solvent was 50%, and the proportion of ethylene glycol dimethyl ether was 5%. Battery assembly: A sodium-ion coin cell was assembled using polypropylene as the battery separator. After 100 cycles at 1C current density at room temperature, the capacity retention was 75%, with an initial coulombic efficiency of 78%.

[0063] The rest is the same as in Example 1, and will not be repeated here.

[0064] Table 1. Comparison of battery design and performance between each embodiment and the comparative example.

[0065]

[0066]

[0067] Based on the test results of Examples 1-4 and Comparative Examples 1-4, it is evident that when the ratio of negative electrode capacity to positive electrode capacity per unit area is within the range of 0.1 to 0.8, the battery exhibits high initial coulombic efficiency and cycle performance. The specially formulated electrolyte synergistically suppresses the formation of sodium dendrites, which is beneficial for improving battery cycle performance. According to the test results of Comparative Example 1, when the negative electrode active material loading is at a normal level, the battery exhibits the best cycle performance and initial coulombic efficiency. However, a normal loading of negative electrode active material is not conducive to reducing battery cost or increasing battery energy density. According to Comparative Example 2, the chain carbonate solvent content in the electrolyte formulation is below 40%; according to Comparative Example 4, the ether solvent content is below 10%. At these levels, the battery cycle performance and initial coulombic efficiency are significantly affected. Excessively low levels of chain carbonate solvent or ether solvent both lead to the formation of sodium dendrites and an increase in side reactions. In particular, excessively low levels of chain solvent reduce solid-liquid contact compatibility, especially the compatibility between the separator and the electrolyte, resulting in excessive battery polarization and preventing the low-loading negative electrode design from achieving normal battery performance. According to Comparative Example 3, when the positive electrode capacity is less than 0.1, the loading of the negative electrode active material is too low, causing some sodium metal to nucleate outside the negative electrode active material. This is especially true where the negative electrode active material does not completely cover the current collector, where sodium metal is directly deposited on the current collector. This deposition overpotential is very high, leading to the formation of sodium dendrites and side reactions. Therefore, a negative electrode active material loading between 0.1 and 0.8 can reduce battery costs, increase battery energy density, and maintain battery cycle performance and initial coulombic efficiency.

[0068] According to the test results of Examples 5 to 10, selecting different positive and negative active materials does not affect the battery performance of the low-load negative electrode design.

[0069] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A sodium-ion battery, characterized in that, It consists of a positive electrode, a negative electrode, a separator, and an electrolyte; The electrolyte is composed of an organic solvent, additives, and sodium salts; the additives in the electrolyte are a certain amount of rubidium salts or cesium salts. The organic solvent is composed of cyclic carbonate solvent, chain carbonate solvent and ether solvent, wherein the proportion of chain carbonate solvent is greater than or equal to 40% and the proportion of ether solvent is greater than or equal to 10% and less than or equal to 60%; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material coating applied to the negative electrode current collector. The negative electrode active material coating includes carbon materials and polymer binders. The active material coating in the negative electrode sheet has a low loading capacity, meaning that the amount of negative electrode active material used is significantly lower than that used in traditional batteries, and satisfies the following formula: Where Ac is the initial charge specific capacity of the negative electrode active material, expressed in mAh / g, and Aw is the coating amount of the negative electrode active material, expressed in g / cm³. 2 Qc represents the initial discharge specific capacity of the positive electrode active material, expressed in mAh / g; Qw represents the coating amount of the positive electrode active material, expressed in g / cm³. 2 ; The carbon material in the coating of the negative electrode active material is selected from hard carbon or soft carbon; The chain carbonate solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; the cyclic carbonate solvent is selected from one or more of ethylene carbonate, propylene carbonate, and butene carbonate. The ether solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethyl ether, tetraethylene glycol dimethyl ether, and methyl tert-butyl ether.

2. The sodium-ion battery according to claim 1, characterized in that, The carbon material accounts for 90% to 98% of the mass of the negative electrode active material coating.

3. The sodium-ion battery according to claim 1, characterized in that, The specific surface area of ​​the negative electrode active material is ≥2m². 2 / g.

4. The sodium-ion battery according to claim 1, characterized in that, The rubidium salt or cesium salt is one or more of its corresponding hexafluorophosphate, tetrafluoroborate, difluorosulfonyl imide salt, trifluoromethanesulfonate, perchlorate, and ditrifluoromethanesulfonyl imide salt.

5. The sodium-ion battery according to claim 4, characterized in that, The amount of rubidium salt or cesium salt added is 0.01% to 0.1% of the electrolyte mass.

6. The sodium-ion battery according to any one of claims 1-5, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material coating applied to the surface of the positive current collector; the positive active material coating includes a positive active material, a binder, and a conductive agent; the positive active material includes one or more of transition metal oxide positive electrode materials, polyanionic compounds, and Prussian blue compounds.

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