Sodium ion battery and electric device

Abstract

Embodiments of the present application disclose a sodium ion battery and an electric device. The sodium ion battery comprises: a positive electrode; a negative electrode, comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being arranged on the negative electrode current collector, the thickness of the negative electrode active material layer being D1 μm, and the porosity being ρ%; and an electrolyte, comprising a sodium salt, a solvent, and a surfactant, the content of the surfactant being W0% on the basis of the total mass of the electrolyte, and the hydrophile-lipophile balance (HLB) value of the surfactant being HLB and satisfying the following relationship: 80≤D1*ρ*HLB / (100*W0)≤1000. The HLB value of the surfactant is regulated and controlled to match the porosity of the negative electrode active material layer, promoting the infiltration of the electrolyte into the pore structure, thus improving the cycle performance and the rate capability of the sodium ion battery.

Description

Sodium-ion batteries and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 23, 2024, with application number 202410101387.3 and application name “Sodium Ion Batteries and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery and electrical equipment. Background Art

[0003] Lithium-ion batteries are currently the most widely commercialized electrochemical energy storage device. They convert chemical energy into electrical energy through the reversible insertion and extraction of lithium ions between the positive and negative electrodes. Sodium and lithium belong to the same main group, but sodium reserves on Earth are far greater than lithium. my country has abundant sodium resources and sodium extraction technology, so the cost of sodium-ion batteries is significantly lower than that of lithium-ion batteries.

[0004] However, the anodes commonly used in sodium-ion batteries currently suffer from large surface areas and numerous surface defects. This results in the formation of a thicker SEI (Solid Electrolyte Interface) layer on the anode surface, which increases the consumption of active sodium. Furthermore, the electrolytes in commercial sodium-ion batteries primarily use carbonate solvents, which have high viscosity and surface tension, resulting in poor pore penetration, leading to reduced battery discharge capacity and energy density. Summary of the Invention

[0005] Based on this, the present application provides a sodium ion battery and electrical equipment with high energy density, high discharge specific capacity and high cycle stability.

[0006] In a first aspect, an embodiment of the present application provides a sodium ion battery, the sodium ion battery comprising:

[0007] A positive electrode; a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer is disposed on the negative electrode current collector, the negative electrode active material layer has a thickness of D1 μm and a porosity of ρ%;

[0008] The electrolyte comprises a sodium salt, a solvent and a surfactant. Based on the total mass of the electrolyte, the surfactant content is W0%, the hydrophile-lipophile balance value of the surfactant is HLB (Hydrophile-Lipophile Balance), and satisfies the following relationship: 80≤D1*ρ*HLB / (100*W0)≤1000.

[0009] In the implementation manner of the present application, W0 satisfies: 0<W0≤5, and HLB satisfies: 3≤HLB≤12.

[0010] In the implementation manner of the present application, D1 satisfies: 70≤D1≤150.

[0011] In the implementation manner of the present application, ρ satisfies: 10≤ρ≤40.

[0012] In the embodiment of the present application, the surfactant includes one or more of stearic acid, sodium dodecylbenzenesulfonate, quaternary ammonium compounds, lecithin, betaine-type compounds, alkyl glucoside, fatty acid glyceride, fatty acid sorbitan, and polysorbate.

[0013] In an embodiment of the present application, the negative electrode active material layer comprises a first negative electrode active material capable of inserting and extracting sodium ions, wherein the first negative electrode active material comprises one or more carbon materials such as hard carbon, natural graphite, artificial graphite, soft carbon, carbon black, acetylene black, carbon nanotubes, graphene, carbon nanofibers, and titanium oxide; and / or,

[0014] The negative electrode active material layer includes a second negative electrode active material capable of alloying with sodium, wherein the second negative electrode active material includes a single substance, oxide or carbide of one or more elements selected from the group consisting of Si, Ge, Pb, In, Zn, Ca, Sr, Ba, Ru and Rh; and / or,

[0015] The negative electrode active material layer includes a third negative electrode active material capable of undergoing a conversion reaction with sodium ions. The third negative electrode active material includes one or more of a transition metal oxide and a transition metal sulfide.

[0016] In an embodiment of the present application, the positive electrode includes a positive electrode active material that can extract and embed sodium ions, including sodium iron composite oxide, sodium cobalt composite oxide, sodium chromium composite oxide, sodium manganese composite oxide, sodium nickel composite oxide, sodium nickel titanium composite oxide, sodium nickel manganese composite oxide, sodium iron manganese composite oxide, sodium nickel cobalt manganese composite oxide, sodium iron phosphate compound, sodium manganese phosphate compound, sodium cobalt phosphate compound, sodium vanadium phosphate compound, sodium vanadium fluorophosphate compound or more.

[0017] In the embodiment of the present application, the sodium salt comprises one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonylimide), sodium bis(trifluoromethylsulfonylimide), sodium perchlorate, 4,5-dicyano-2-(trifluoromethyl)imidazolium sodium, and 4,5-dicyano-2-(pentafluoroethyl)imidazolium sodium. Based on the total mass of the electrolyte, the content of the sodium salt is Ws%, 5≤Ws≤30.

[0018] In the embodiment of the present application, the solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. Based on the total mass of the electrolyte, the content of the solvent is W1%, 50≤W1<90.

[0019] In an embodiment of the present application, the electrolyte further includes a film-forming additive, and the film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1-propylene-1,3-sultone, vinyl ethylene carbonate, vinyl sulfate, methylene dicarbonate, tris(trimethylsilyl) phosphate, succinic anhydride, maleic anhydride, etc., and the total content of the additive is W2% based on the total mass of the electrolyte, 0<W2≤10.

[0020] The present application introduces a surfactant into the electrolyte and matches the hydrophilic-lipophilic balance value of the selected surfactant with the thickness and porosity of the negative electrode active material layer to promote the infiltration of the electrolyte into the negative electrode active material layer, alleviate the risk of sodium desorption, increase the discharge capacity and energy density of the battery, and improve the cycle stability. It is also beneficial to reduce battery polarization and improve the battery's rate discharge capability.

[0021] In a second aspect, embodiments of the present application further provide an electrical device comprising the sodium-ion battery of the first aspect. The sodium-ion battery has a long cycle life and good rate performance, enabling the electrical device to be used stably for a long period of time, thereby improving the performance of the electrical device. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used in this application includes any and all combinations of one or more of the relevant listed items.

[0024] The following describes some embodiments of the present application in detail. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0025] Lithium-ion batteries are currently the most widely commercialized electrochemical energy storage device. They convert chemical energy into electrical energy through the reversible insertion and extraction of lithium ions between the positive and negative electrodes. Sodium and lithium belong to the same main group, but sodium reserves on Earth are far greater than lithium. my country has abundant sodium resources and sodium extraction technology, so the cost of sodium-ion batteries is significantly lower than that of lithium-ion batteries.

[0026] In addition to their storage and cost advantages, sodium-ion batteries generate less transient heat during safety testing, offering greater safety. Furthermore, sodium ions have a lower desolvation rate in organic solvents, resulting in higher ion conductivity and lower charge transfer resistance under the same conditions. Furthermore, sodium and aluminum do not form alloys at low potentials, allowing the use of aluminum as current collectors in both the positive and negative electrodes of sodium-ion batteries, increasing the battery's energy density.

[0027] However, the anodes commonly used in current sodium-ion batteries suffer from large surface areas and numerous surface defects. This results in the formation of a thicker SEI layer on the anode surface, which increases the consumption of active sodium. Furthermore, the electrolytes in commercial sodium-ion batteries primarily use carbonate solvents, which have high viscosity and surface tension, resulting in poor pore wetting, leading to reduced battery discharge capacity and energy density.

[0028] Based on this, an embodiment of the present application provides a sodium ion battery, comprising: a positive electrode; a negative electrode, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer can be coated on one side of the negative electrode current collector or on both sides, and the thickness of the single-layer negative electrode active material layer is D1μm, and the porosity is ρ%; an electrolyte, the electrolyte comprising a sodium salt, a solvent and a surfactant, the surfactant content is W0%, the hydrophilic-lipophilic balance value of the surfactant is HLB, and the following relationship is satisfied: 80≤D1*ρ*HLB / (100*W0)≤1000. The hydrophilic-lipophilic balance (HLB) value of a surfactant quantitatively represents the hydrophilic-lipophilic properties of the surfactant. The lower the HLB value, the better the lipophilicity (organic) property. The turning point between lipophilicity and hydrophilicity is about 10. Near this value, the surfactant molecules have a high comprehensive hydrophilic-lipophilic ability; for example, paraffin has HLB = 0, which means no hydrophilicity; polyethylene glycol has HLB = 20, which means completely hydrophilic. This matches the porosity in the negative electrode active material layer, thereby promoting the infiltration of the electrolyte into the pore structure and the capacity of the negative electrode, thereby improving the utilization rate of the active material. D1*ρ is positively correlated with the contact area of ​​the electrode / electrolyte, and (100*W0) / HLB is positively correlated with the wettability of the electrolyte. The greater the thickness and the higher the porosity, the higher the wettability of the electrolyte is required to ensure sufficient contact and wetting between the electrode and the electrolyte. The electrode / electrolyte contact area (D1*ρ) and the electrolyte wettability (100*W0) / HLB need to match to ensure a high ion transport capacity at the electrode / electrolyte interface. During the implementation process, it was found that the value of D1*ρ*HLB / (100*W0) is between 80 and 1000, and the battery has good overall performance. In one embodiment, D1*ρ*HLB / (100*W0) can be 80, 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000.

[0029] In one embodiment, W0 satisfies: 0<W0≤5, and HLB satisfies: 3≤HLB≤12. The hydrophilic-lipophilic balance value HLB of the surfactant reflects the comprehensive affinity of the hydrophilic and lipophilic groups in the surfactant molecule to oil or water. The higher the HLB value, the stronger the hydrophilicity, and vice versa, the stronger the lipophilicity. Surfactant molecules with an HLB value between 3 and 12 have better comprehensive hydrophilic and lipophilic abilities. Optionally, the HLB value can be 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. As an inert component in the electrolyte, the surfactant can avoid reducing the ion transport capacity of the electrolyte within this content. Optionally, based on the total mass of the electrolyte, the value of W0 can be 0.5, 1, 2, 3, 4, or 5.

[0030] In one embodiment, D1 satisfies the following: 70 ≤ D1 ≤ 150. Within this range, the negative electrode can simultaneously have a high active material loading and a moderate ion transport path, thereby ensuring high energy density and fast ion transport kinetics. Optionally, based on the total mass of the electrolyte, the value of D1 can be 70, 80, 90, 100, 110, 120, 130, 140, or 150.

[0031] In one embodiment, ρ satisfies the following: 10 ≤ ρ ≤ 40. Within this range, the internal porosity of the electrode is moderate, ensuring tight connectivity of the electron transport channels within the electrode while also reducing the thickness of the battery cell and increasing the volumetric energy density. Optionally, the value of ρ can be 10, 15, 25, 30, 35, or 40.

[0032] In one embodiment, the surfactant includes one or more of stearic acid, sodium dodecylbenzenesulfonate, quaternary ammonium compounds, lecithin, betaine-type compounds, alkyl glucoside, fatty acid glycerides, fatty acid sorbitan, and polysorbate.

[0033] The main role of surfactants in sodium-ion batteries is to reduce the surface tension of the electrolyte and improve the wettability of the electrolyte on the surface of the electrode (the electrode is the positive electrode or the negative electrode), so that the electrolyte can smoothly penetrate the internal pores of the electrode, promote the insertion and extraction of sodium ions, and facilitate the development of active capacity. Especially under high-rate charge and discharge conditions, the improvement of the wettability between the electrolyte and the electrode can effectively alleviate the sodium precipitation phenomenon caused by excessive local sodium ion flux. For example, sodium dodecylbenzenesulfonate is an anionic surfactant. The anionic functional groups in its molecular structure can combine with defects and oxygen-containing functional groups on the surface of the negative electrode, and the other end can form a complex with the solvent in the electrolyte, thereby reducing the surface tension of the electrode and promoting the electrolyte to penetrate the electrode surface and pores. It can also play a certain role in corrosion resistance.

[0034] In one embodiment, the negative electrode current collector is aluminum foil. In sodium ion batteries, aluminum foil can be used for both positive and negative electrode current collectors because sodium and aluminum do not react to form alloys, and the cost is much lower than copper foil in lithium batteries.

[0035] The negative electrode active material layer includes a first negative electrode active material capable of embedding and de-embedding sodium ions, wherein the first negative electrode active material includes one or more carbon materials such as hard carbon, natural graphite, artificial graphite, soft carbon, carbon black, acetylene black, carbon nanotubes, graphene, carbon nanofibers, and titanium oxide; and / or, the negative electrode active material includes a second negative electrode active material capable of alloying with sodium, wherein the second negative electrode active material includes a simple substance, oxide or carbide of one or more elements selected from Si, Ge, Pb, In, Zn, Ca, Sr, Ba, Ru, and Rh; and / or, the negative electrode active material includes a third negative electrode active material capable of conversion reaction with sodium ions, wherein the third negative electrode active material includes one or more transition metal oxides and transition metal sulfides.

[0036] The anode active material of sodium-ion batteries possesses the ability to intercalate and deintercalate sodium ions, which is crucial for ensuring normal charge and discharge. Among a given anode active material, carbon materials such as hard carbon, natural graphite, artificial graphite, soft carbon, carbon black, acetylene black, carbon nanotubes, graphene, and carbon nanofibers exhibit excellent conductivity and plasticity, and are capable of intercalating and deintercalating sodium ions. These carbon materials can be used alone or in combination to enhance the performance of the anode material. Furthermore, some metal or non-metal elements, such as Si, Ge, Pb, In, Zn, Ca, Sr, and Ba, can alloy with sodium. During discharge, sodium alloys can also undergo dealloying reactions, converting chemical energy into electrical energy. Therefore, these single-element materials can also serve as anode materials for sodium-ion batteries. Furthermore, oxides and sulfides containing these elements can also undergo conversion reactions with sodium ions and serve as anode active materials. Therefore, the negative electrode materials of sodium-ion batteries use materials with different properties, aiming to achieve the embedding and extraction of sodium ions through different mechanisms, thereby improving the energy density and cycle life of the battery.

[0037] In one embodiment, the positive electrode of the sodium ion battery includes a positive electrode active material capable of extracting and inserting sodium ions, including one or more of sodium iron composite oxide, sodium cobalt composite oxide, sodium chromium composite oxide, sodium manganese composite oxide, sodium nickel composite oxide, sodium nickel titanium composite oxide, sodium nickel manganese composite oxide, sodium iron manganese composite oxide, sodium nickel cobalt manganese composite oxide, sodium iron phosphate, sodium manganese phosphate, sodium cobalt phosphate, sodium vanadium phosphate, and sodium vanadium fluorophosphate. These composite oxides have a variety of crystal structures, such as layered structures and tunnel structures, which are conducive to the insertion and extraction of sodium ions, thereby improving the charge and discharge performance of the battery.

[0038] In one embodiment, the sodium salt comprises one or more of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl imide), sodium bis(trifluoromethylsulfonyl imide), sodium perchlorate, sodium 4,5-dicyano-2-(trifluoromethyl)imidazolium, and sodium 4,5-dicyano-2-(pentafluoroethyl)imidazolium. Sodium salt is the primary electrolyte in sodium ion batteries, conducting sodium ions and enabling the battery to undergo charge and discharge reactions.

[0039] Based on the total mass of the electrolyte, the content of sodium salt is Ws%, 5≤Ws≤30. The concentration of sodium salt has an important influence on the performance of sodium ion batteries. Sodium salt with an appropriate concentration can improve the conductivity of the battery, thereby improving the energy density and charge-discharge performance of the battery. Optionally, based on the total mass of the electrolyte, the content of sodium salt in the sodium ion battery electrolyte can be 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, 23%, 25%, 27%, or 30%. In one embodiment, the solvent in the sodium ion battery electrolyte includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The solvent can combine with sodium ions to form solvated ions, which helps to stabilize the sodium ions and enable them to be better transported in the electrode material. Based on the total mass of the electrolyte, the content of the solvent is W1%, 50≤W1<90. Optionally, the content of sodium salt in the sodium ion battery electrolyte can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%. In one embodiment, the electrolyte further includes a film-forming additive, and the film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1-propylene-1,3-sultone, vinyl ethylene carbonate, vinyl sulfate, methylene dicarbonate, tris(trimethylsilyl)phosphate, succinic anhydride, and maleic anhydride. Some additives can increase the conductivity of the electrolyte, thereby accelerating the transmission speed of electrons and ions, improving the charge and discharge performance of the battery, inhibiting side reactions and adjusting the interface properties, thereby improving the electrochemical performance of the electrode. Based on the total mass of the electrolyte, the total content of the film-forming additive is W2%, 0<W2≤10. Alternatively, the content of the film-forming additive may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0040] The present application also provides an electrical device comprising a sodium-ion battery according to any of the above embodiments. Specifically, the electrical device may be an electric vehicle, an electric motorcycle, an electric bicycle, a power bank, an unmanned aerial vehicle, a mobile phone, a computer, a camera, a power tool, a smart home device, or a wearable device.

[0041] The electrical equipment provided in the embodiment of the present application includes a sodium ion battery, which has a long cycle life and good rate performance, so that the electrical equipment can be used stably for a long time, which is beneficial to improving the performance of the electrical equipment.

[0042] The technical solution of the present application is further illustrated below through specific examples and comparative examples.

[0043] Example 1

[0044] (1) Preparation of electrolyte

[0045] In an argon atmosphere glove box with a water content of <1 ppm and an oxygen content of <1 ppm, propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 4:4:2. A surfactant was then added, followed by sodium hexafluorophosphate (NaPF6) to prepare an electrolyte with a NaPF6 concentration of 1 mol / L. The surfactant types and contents are shown in Table 1.

[0046] (2) Preparation of positive electrode sheet

[0047] The positive electrode active material sodium manganese composite oxide (NaMnO2), the conductive agent carbon nanotubes (CNT, Carbon Nanotubes), and the binder polyvinylidene fluoride are mixed in a mass ratio of 95:2:3, and N-methylpyrrolidone (NMP, N-Methylpyrrolidone) is added. The mixture is stirred into a uniform positive electrode slurry under the action of a vacuum mixer, and then the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil; after drying at 85°C, it is cold pressed, cut into pieces, and slit, and then dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.

[0048] (3) Negative electrode preparation

[0049] The negative electrode active material, hard carbon, the conductive agent, acetylene black, the binder, styrene butadiene rubber (SBR), and the dispersant, carboxymethylcellulose (CMC), were thoroughly mixed in a deionized water solvent system at a mass ratio of 93.5:2:2.5:2. The mixture was then coated onto aluminum foil, dried, and cold-pressed to produce a negative electrode sheet. The porosity and thickness of the negative electrode sheet are shown in Table 1.

[0050] (4) Diaphragm preparation

[0051] The diaphragm is made of polypropylene.

[0052] (5) Preparation of sodium ion batteries

[0053] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. Then they are wound and placed in the outer packaging foil. The prepared electrolyte is injected into the dried electrode core. After vacuum packaging, standing, formation, shaping and other processes, the preparation of the sodium ion battery is completed.

[0054] Examples 2 to 16

[0055] The types and contents of surfactants, thickness and porosity of the negative electrode sheets of Examples 2 to 16 are shown in Table 1. The remaining steps are the same as those of Example 1.

[0056] Comparative Examples 1 to 10

[0057] The types and contents of surfactants, thickness and porosity of the negative electrode sheets of Comparative Examples 1 to 10 are shown in Table 1. The remaining steps are the same as those of Example 1.

[0058] Table 1 Negative electrode active material layer and surfactant selection

[0059] Test method:

[0060] (1) Normal temperature cycle test

[0061] The prepared sodium ion battery was charged to 3.95V at a constant current of 0.5C at room temperature (25±3℃), then charged to a current of 0.05C at 3.95V, left for 5min, and then discharged to 1.5V at a constant current of 0.5C, left for 5min, which was considered a cycle. The capacity retention rate (the ratio of the discharge capacity after 1000 cycles to the discharge capacity of the first cycle) and the thickness expansion rate (1000 full-charge thickness / first full-charge thickness) after 1000 cycles at room temperature were recorded. The cycle was performed using a NEWARE test cabinet (model CTE-4080D-5V30A). To ensure that the battery temperature was constant during the cycle test, the battery was placed in a high and low temperature test chamber (model CH1000T). The battery thickness was tested using a PPG tester (model ATMPPGSH200).

[0062] (2) Low temperature cycle test

[0063] The prepared sodium-ion battery was charged at 12°C (12±3°C) at a constant current rate of 0.5C to 3.95V. It was then charged at a constant voltage at 3.95V to a current of 0.05C, held for 5 minutes, and then discharged at a constant current rate of 0.5C to 1.5V, held for 5 minutes. This constituted one cycle. The capacity retention after 600 low-temperature cycles was recorded.

[0064] (3) Normal temperature rate test

[0065] The prepared sodium ion battery was charged to 3.95V at a constant current and constant voltage rate of 0.2C at room temperature (25±3℃), cut off at 0.05C, and left for 5 minutes, then discharged to 1.5V at a constant current rate of 0.2C and left for 5 minutes, which was considered as one cycle. After two 0.2C cycles, the discharge capacity of the second cycle was taken as the 0.2C discharge capacity. The battery was then charged to 3.95V at a constant current and constant voltage rate of 0.5C, cut off at 0.05C, and left for 5 minutes, then discharged to 1.5V at a constant current rate of 2C and left for 5 minutes, which was considered as one cycle. After two 2C cycles, the discharge capacity of the second cycle was taken as the 2C discharge capacity. The ratio of the discharge capacity recorded twice is the room temperature 2C / 0.1C capacity retention rate.

[0066] (4) Low-temperature circulation sodium precipitation

[0067] After 600 cycles of low-temperature cycling, the battery is disassembled in a fully charged state and the sodium precipitation on the negative electrode surface is observed. If there is obvious silvery-white metallic product deposition on the large surface of the negative electrode, the tab or the crease, it is considered as sodium precipitation. In the case of severe sodium precipitation, sodium metal will react with the electrolyte to cause the sodium metal to change from silvery white to yellow.

[0068] Table 2 Cyclic test and sodium precipitation test results

[0069] It can be seen from Table 1 and Table 2 that, specifically, by comparing Examples 1 to 16 and Comparative Examples 1 to 10, when the thickness, porosity, surfactant content and hydrophilic-lipophilic balance value of the negative electrode active material layer meet the range of 80≤D1*ρ*HLB / (100*W0)≤1000 as described in this application, the room temperature cycle performance, low temperature cycle performance and rate cycle performance are excellent, and no sodium precipitation occurs. The negative electrode sheet as a whole presents a uniform gray-black morphology, and there is no obvious silvery white or yellow by-product deposition.

[0070] From the above test results, it can be concluded that when the thickness of the negative electrode active material layer is large and the porosity is high, the electrolyte needs to have higher wettability. The lower the HLB value of the surfactant in the electrolyte and the higher the content W0, the better the wetting effect. When D1*ρ*HLB / (100*W0)>1000, it means that the porosity D1*ρ / 100 in the negative electrode active material layer is too large, exceeding the total wetting capacity W0 / HLB of the surfactant additive in the electrolyte. The wettability of the electrolyte to the electrode is insufficient, and the microporous areas not wetted by the electrolyte are difficult to contribute to the active capacity, resulting in a low total discharge capacity of the full battery. More seriously, it will cause the sodium ions deintercalated from the positive electrode to be unable to enter the active area of ​​the negative electrode and thus deposit on the surface, causing sodium precipitation and safety hazards. For example, in Comparative Example 2, after low-temperature cycling, there is obvious silvery-white metallic sodium deposition at the crease of the negative electrode sheet. When D1*ρ*HLB / (100*W0) is less than 80, as in Comparative Examples 3 to 10, an excessively high proportion of surfactants accumulates on the positive and negative electrode surfaces, which indeed improves the wettability of the electrolyte to the electrodes. However, the inert adsorption layer prevents sodium ions from contacting the positive and negative electrode active materials, hindering ion / electron transport, increasing battery polarization, and reducing rate discharge capacity. Furthermore, due to the poor oxidative stability of the surfactant, the surfactant undergoes irreversible oxidative decomposition on the positive electrode surface. Side reactions prevent the current from being reduced below the constant voltage cutoff current during the charging process. The accumulation of side reaction products on the positive electrode side further increases the positive electrode impedance, increases polarization, and further reduces the positive electrode active capacity. On the other hand, excessive accumulation of surfactant molecules on the surface of the negative electrode will prevent sodium ions from entering the interior of the negative electrode, but instead they gain electrons on the surface for reduction, resulting in sodium precipitation on the negative electrode. For example, in Comparative Example 4, after low-temperature cycling, the negative electrode sheet exhibits large-area sodium precipitation, and irreversible redox reactions occur between sodium metal and electrolyte solvents and additive molecules, resulting in the accumulation of side reaction products. A large amount of silver-white and brown-yellow reaction products accumulate on the surface of the negative electrode sheet. The highly active sodium will catalyze the reduction of the electrolyte to produce gas, and the continued growth of sodium dendrites may puncture the diaphragm, causing battery short circuits and serious safety problems.

[0071] The above is a preferred embodiment of the present application, but it should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present application, and such improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A sodium-ion battery, characterized in that, The sodium-ion battery includes: a positive electrode; a negative electrode, the negative electrode comprising a negative current collector and a negative active material layer disposed on the negative current collector, the thickness of the negative active material layer being D1 μm and the porosity being ρ%; an electrolyte, the electrolyte comprising a sodium salt, a solvent and a surfactant, based on the total mass of the electrolyte, the content of the surfactant being W0%, the hydrophilic-lipophilic balance value of the surfactant being HLB, and satisfying the following relationship: 80 ≤ D1 * ρ * HLB / (100 * W0) ≤ 1000.

2. The sodium ion battery according to claim 1, characterized in that, The W0 satisfies: 0 < W0 ≤ 5, and the HLB satisfies: 3 ≤ HLB ≤ 12.

3. The sodium-ion battery according to claim 1, wherein, The D1 satisfies: 70 ≤ D1 ≤ 150.

4. The sodium ion battery according to claim 1, wherein The ρ satisfies: 10 ≤ ρ ≤ 40.

5. The sodium ion battery according to claim 1, characterized in that, The surfactant includes one or more of stearic acid, sodium dodecylbenzenesulfonate, quaternary ammonium compounds, lecithin, betaine-type compounds, alkyl glucosides, fatty acid glycerides, sorbitan fatty acid esters, and polysorbates.

6. The sodium ion battery according to claim 1, wherein The negative active material layer contains a first negative active material capable of intercalating and deintercalating sodium ions, the first negative active material including one or more of carbon materials such as hard carbon, natural graphite, artificial graphite, soft carbon, carbon black, acetylene black, carbon nanotubes, graphene, carbon nanofibers, and titanium oxides; and / or, The negative active material layer includes a second negative active material capable of alloying reaction with sodium, the second negative active material including one or more of elements such as Si, Ge, Pb, In, Zn, Ca, Sr, Ba, Ru, and Rh, single substances, oxides or carbides; and / or, The negative active material layer includes a third negative active material capable of conversion reaction with sodium ions, the third negative active material including one or more of transition metal oxides and transition metal sulfides.

7. The sodium-ion battery according to claim 1, characterized in that, The sodium salt includes one or several of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium perchlorate, 4,5-dicyano-2-(trifluoromethyl)imidazole sodium salt, 4,5-dicyano-2-(pentafluoroethyl)imidazole sodium salt, based on the total mass of the electrolyte, the content of the sodium salt being Ws%, 5 ≤ Ws ≤ 30.

8. The sodium ion battery according to claim 1, characterized in that, The solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, based on the total mass of the electrolyte, the content of the solvent being W1%, 50 ≤ W1 < 90.

9. The sodium ion battery according to claim 1, wherein, The electrolyte further includes a film-forming additive, the film-forming additive including one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1-propene-1,3-sultone, ethylene carbonate ethylene ester, ethylene sulfate, methylene methane dicarbonate, tris(trimethylsilyl) phosphate, succinic anhydride, and maleic anhydride, based on the total mass of the electrolyte, the total content of the film-forming additive being W2%, 0 < W2 ≤ 10.

10. An electrical device, characterized in that, Comprising the sodium-ion battery according to any one of claims 1 to 9.

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