CN116014249B - Electrolyte, sodium ion battery and electricity utilization device - Google Patents

Abstract

The application provides an electrolyte, a sodium ion battery and an electrical device. The electrolyte solution includes S-containing anions and B-containing anions, the S-containing anions include at least one of N(FSO ₂ ) ₂ ^‑ and N(CF ₃ SO ₂ ) ₂ ^‑ , and the B-containing anions include B(F ₂ C ₂ O ₄ ) ^‑ and BF ₄ ^‑ , the molar ratio of S element to B element in the electrolyte is (2~20):1. When the electrolyte is applied to a sodium-ion battery, a solid electrolyte interfacial film (SEI film) containing S elements and B elements will be formed on the surface of the negative electrode of the battery. Better toughness helps to improve the storage capacity retention rate of sodium-ion batteries.

Description

Electrolyte, sodium ion battery and electrical device

Technical Field

The present application relates to the technical field of secondary batteries, and in particular to an electrolyte, a sodium ion battery and an electrical device.

Background Art

The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

As a secondary battery, sodium-ion batteries mainly rely on the movement of sodium ions between the positive and negative electrodes to work. In the field of secondary batteries, sodium-ion batteries have a good cost advantage, which is conducive to broadening the scope of use of sodium-ion batteries. However, the storage capacity retention rate of sodium-ion batteries needs to be further improved.

Summary of the invention

The present application provides an electrolyte. The electrolyte includes S-containing anions and B-containing anions, the S-containing anions include at least one of N(FSO ₂ ) ₂ ^- and N(CF ₃ SO ₂ ) ₂ ^- , the B-containing anions include at least one of B(F ₂ C ₂ O ₄ ) ^- and BF ₄ ^- , and the molar ratio of the S element to the B element in the electrolyte is (2-20):1.

The electrolyte of the present application includes corresponding S-containing anions and B-containing anions, as well as S elements and B elements in corresponding molar ratios. When the electrolyte is applied to a sodium ion battery, a solid electrolyte interface film (SEI film) containing S elements and B elements is formed on the negative electrode surface of the battery. The SEI film can take into account both a more efficient sodium ion transmission rate and better toughness, which helps to improve the storage capacity retention rate of the sodium ion battery.

In some embodiments, in the electrolyte, the molar concentration of S element is 1 mol/L~4 mol/L.

In some embodiments, in the electrolyte, the molar concentration of element B is 0.1 mol/L to 1 mol/L.

In some embodiments, the electrolyte further contains at least one of F element and N element.

In some embodiments, the electrolyte contains F element and N element, wherein the molar ratio of F element to N element is (2.2~10):1.

In some of the embodiments, in the electrolyte, the molar concentration of the F element is 1.4 mol/L to 6.8 mol/L.

In some embodiments, in the electrolyte, the molar concentration of N element is 0.5 mol/L~2 mol/L.

In some embodiments, the electrolyte includes a S-containing sodium salt and a B-containing sodium salt.

In some embodiments, the S-containing sodium salt includes at least one of sodium bis(trifluoromethylsulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide.

In some embodiments, the B-containing sodium salt includes at least one of sodium difluorooxalatoborate and sodium tetrafluoroborate.

In some embodiments, the electrolyte further includes an additive, wherein the additive includes an alkyl sodium salt.

In some embodiments, the alkyl sodium salt includes at least one of sodium lauryl sulfate and sodium poly(dipropylene glycol disulfide) sulfonate.

In some embodiments, the molar concentration of the additive is 0.001 mol/L to 0.015 mol/L.

In some embodiments, the solvent in the electrolyte includes at least one of ethylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, methyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran and methyltetrahydrofuran.

The present application also provides a sodium ion battery, comprising the above-mentioned electrolyte.

The present application also provides an electrical device, comprising the above-mentioned sodium ion battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

FIG. 3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

Description of reference numerals:

1. Secondary battery; 11. Shell; 12. Electrode assembly; 13. Top cover assembly; 2. Electrical device.

DETAILED DESCRIPTION

Below, the battery assembly, battery cell, secondary battery and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true or exists, and B is false or does not exist; A is false or does not exist, and B is true or exists; or both A and B are true, or both A and B exist.

If there is no special explanation, in this application, the terms "positive electrode sheet" and "positive electrode sheet" have the same meaning and can be used interchangeably. The terms "negative electrode sheet" and "negative electrode sheet" have the same meaning and can be used interchangeably. The terms "diaphragm" and "separation membrane" have the same meaning and can be used interchangeably.

An embodiment of the present application provides an electrolyte. The electrolyte includes S-containing anions and B-containing anions, the S-containing anions include at least one of N(FSO ₂ ) ₂ ^- and N(CF ₃ SO ₂ ) ₂ ^- , the B-containing anions include at least one of B(F ₂ C ₂ O ₄ ) ^- and BF ₄ ^- , and the molar ratio of S element to B element in the electrolyte is (2~20):1. The electrolyte includes corresponding S-containing anions and B-containing anions, as well as S element and B element in corresponding molar ratios. When the electrolyte is applied to a sodium ion battery, a solid electrolyte interface film (SEI film) containing S element and B element will be formed on the negative electrode surface of the battery. The SEI film can take into account both a more efficient sodium ion transmission rate and better toughness, which helps to improve the storage capacity retention rate of the sodium ion battery. When the molar ratio of the S element to the B element is too large, the toughness of the SEI film may be poor, and it is easy to rupture and damage during the cycle, resulting in poor electrical performance. When the molar ratio of S element to B element is too small, the transmission rate of sodium ions in the SEI film may deteriorate, resulting in increased impedance and polarization, which in turn leads to a decrease in electrical performance.

It is understood that the S element and the B element in the electrolyte can be provided by S anions and B anions. Further optionally, the S anions serve as the source of the S element, and the B anions serve as the source of the B element. It is also understood that the electrolyte may contain other substances containing the S element and/or the B element, and these substances can also provide a certain amount of the S element and the B element.

As some optional examples of the molar ratio of the S element and the B element, the molar ratio of the S element and the B element can be, but is not limited to, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, etc. It is understood that the molar ratio of the S element and the B element can also be selected in the range of (2 to 20): 1. Further, the molar ratio of the S element and the B element can be selected from the molar ratios of the S element and the B element described in the embodiments below in this application.

As an example of the molar concentration of the S element in the electrolyte, in the electrolyte, the molar concentration of the S element is 1 mol/L to 4 mol/L. Optionally, in the electrolyte, the molar concentration of the S element is 1 mol/L, 1.2 mol/L, 1.5 mol/L, 1.8 mol/L, 2 mol/L, 2.2 mol/L, 2.5 mol/L, 2.8 mol/L, 3 mol/L, 3.2 mol/L, 3.5 mol/L, 3.8 mol/L, 4 mol/L, etc.

As an example of the molar concentration of element B in the electrolyte, in the electrolyte, the molar concentration of element B is 0.1 mol/L to 1 mol/L. Optionally, in the electrolyte, the molar concentration of element B is 0.1 mol/L, 0.2 mol/L, 0.3 mol/L, 0.4 mol/L, 0.5 mol/L, 0.6 mol/L, 0.7 mol/L, 0.8 mol/L, 0.9 mol/L, 1 mol/L, etc.

It is understood that, in the electrolyte, the molar concentration of the S element can also be selected in the range of 1 mol/L to 4 mol/L. In the electrolyte, the molar concentration of the B element can also be selected in the range of 0.1 mol/L to 1 mol/L. Further, in the electrolyte, the molar concentration of the S element can also be selected from the molar concentrations of the S element described in the embodiments below in this application. In the electrolyte, the molar concentration of the B element can also be selected from the molar concentrations of the B element described in the embodiments below in this application.

It can be understood that the types and molar concentrations of elements in this application can be measured by reference to Inductively Coupled Plasma Atomic Emission Spectrometry (EPA 6010D-2018), Inductively Coupled Plasma Atomic Emission Spectrometry General Rules (JY/T 0567-2020) or Lithium Hexafluorophosphate Product Analysis Method (GBT19282-2014). For example, after the sample is pre-treated, the type and molar concentration of the element are obtained by testing with an inductively coupled plasma atomic emission spectrometer. Optionally, the testing method includes: (1) accurately measuring 5 mL of fresh electrolyte sample into a digestion tank, and recording the sample weight after the balance number is stable; (2) slowly adding 10 mL of concentrated HNO ₃ , flushing the sample on the inner wall into the bottom of the tank, and gently shaking the digestion tank; (3) placing the digestion tank in an acid remover and digesting at 180°C for about 30 minutes; (4) when the solution evaporates to 1~2 mL, remove the digestion tank and cool it to room temperature, rinse the tank with ultrapure water 3 times, pour the rinse solution into a 50 mL plastic volumetric flask to make up the volume, and shake it evenly; (5) testing the solution after making up the volume with an inductively coupled plasma atomic emission spectrometer.

It can be understood that the types and molar concentrations of ions in this application can refer to standards JY/T 020-1996 and GB/T36240-2018, and the ion components in the electrolyte are quantitatively analyzed by ion chromatography analysis.

Further, the electrolyte also contains at least one of the F element and the N element. Optionally, the molar ratio of the F element to the N element is (2.2~10):1. For example, the molar ratio of the F element to the N element can be but is not limited to 2.2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, etc. It is understood that the molar ratio of the F element to the N element can also be selected in the range of (2.2~10):1. Optionally, the molar ratio of the F element to the N element is (2.2~6.8):1. Further, the molar ratio of the F element to the N element can also be selected in the molar ratio of the F element to the N element described in the embodiments below in this application.

Specifically, in the electrolyte, the molar concentration of the F element is 1.4mol/L to 6.8mol/L. Optionally, in the electrolyte, the molar concentration of the F element is 1.4mol/L, 1.5mol/L, 1.8mol/L, 2mol/L, 2.5mol/L, 3mol/L, 3.5mol/L, 4mol/L, 4.5mol/L, 5mol/L, 5.5mol/L, 6mol/L, 6.5mol/L, 6.8mol/L, etc. Of course, in the electrolyte, the molar concentration of the F element can also be selected from the molar concentration of the F element described in the embodiments below in this application.

Optionally, the molar concentration of N element is 0.5mol/L~2mol/L. Optionally, in the electrolyte, the molar concentration of N element is 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, 1mol/L, 1.1mol/L, 1.2mol/L, 1.3mol/L, 1.4mol/L, 1.5mol/L, 1.6mol/L, 1.7mol/L, 1.8mol/L, 1.9mol/L, 2mol/L, etc. It is understood that in the electrolyte, the molar concentration of N element can also be selected in the range of 0.5mol/L~2mol/L. Of course, in the electrolyte, the molar concentration of N element can also be selected in the molar concentration of N element recorded in the embodiments below in the present application.

In some embodiments, the electrolyte includes a sodium salt containing S and a sodium salt containing B. Optionally, the sodium salt containing S includes at least one of sodium bis(fluorosulfonyl)imide (N(FSO ₂ ) ₂ Na) and sodium bis(trifluoromethylsulfonyl)imide (N(CF ₃ SO ₂ ) ₂ Na), and the sodium salt containing B includes at least one of sodium difluorooxalatoborate (B(F ₂ C ₂ O ₄ )Na) and sodium tetrafluoroborate (BF ₄ Na).

Optionally, in the electrolyte, the molar ratio of the sodium salt containing S to the sodium salt containing B is (1-10):1. Further optionally, in the electrolyte, the molar ratio of the sodium salt containing S to the sodium salt containing B is 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, etc. It is understood that in the electrolyte, the molar ratio of the sodium salt containing S to the sodium salt containing B can also be selected in the range of (1-10):1. Of course, the molar ratio of the sodium salt containing S to the sodium salt containing B can also be selected in the molar ratio of the sodium salt containing S to the sodium salt containing B described in the embodiments below in this application.

Optionally, in the electrolyte, the molar concentration of the sodium salt containing S is 0.5mol/L to 2mol/L. Optionally, the molar concentration of the sodium salt containing S is 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, 1mol/L, 1.1mol/L, 1.2mol/L, 1.3mol/L, 1.4mol/L, 1.5mol/L, 1.6mol/L, 1.7mol/L, 1.8mol/L, 1.9mol/L, 2mol/L, etc.

Optionally, in the electrolyte, the molar concentration of the sodium salt containing B is 0.1mol/L to 1mol/L. Optionally, in the electrolyte, the molar concentration of the sodium salt containing B is 0.1mol/L, 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, 1mol/L, etc.

In some embodiments, the electrolyte further comprises an additive, and the additive comprises an alkyl sodium salt. The alkyl sodium salt additive can promote the wetting of the electrolyte on the surface of the negative electrode, thereby reducing the content of the battery and further improving the storage capacity retention rate of the battery. Optionally, the alkyl sodium salt comprises at least one of sodium dodecyl sulfate and sodium polydisulfide dipropane sulfonate. Further optionally, the molar concentration of the additive is 0.001 mol/L to 0.015 mol/L. For example, the molar concentration of the additive can be but is not limited to 0.001 mol/L, 0.0015 mol/L, 0.0018 mol/L, 0.002 mol/L, 0.0025 mol/L, 0.003 mol/L, 0.0035 mol/L, 0.004 mol/L, 0.0045 mol/L, 0.005 mol/L, 0.0055 mol/L, 0.006 mol/L, 0.0065 mol/L, 0.007 mol/L, 0.0075 mol/L, 0.008 mol/L, 0.0085 mol/L, 0.009 mol/L, 0.0095 mol/L, 0.01 mol/L, 0.012 mol/L, 0.015 mol/L, etc. It is understood that the molar concentration of the additive can also be selected in the range of 0.0015 mol/L to 0.015 mol/L. Of course, the molar concentration of the additive can also be selected in the molar concentration of the additive described in the examples below.

In some embodiments, the electrolyte further includes a solvent, and the solvent includes at least one of ethylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, methyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran, and methyltetrahydrofuran. Optionally, the solvent includes propylene carbonate and dimethyl carbonate. Further optionally, the volume ratio of propylene carbonate and dimethyl carbonate is (0.5~1.5):1. For example, the volume ratio of propylene carbonate and dimethyl carbonate can be, but is not limited to, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1. Optionally, the molecular weight of polyethylene glycol dimethyl ether is 250-320.

Another embodiment of the present application provides a sodium ion battery. The sodium ion battery includes the above-mentioned electrolyte.

Another embodiment of the present application provides an electrical device, which includes the sodium ion battery.

Hereinafter, the secondary battery will be described with reference to the relevant drawings.

Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[Positive electrode]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material on a polymer material substrate. Optionally, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. Optionally, the polymer material substrate may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

In some embodiments, when the secondary battery is a lithium ion battery, the positive electrode active material may be a positive electrode active material for lithium ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates containing olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their modified compounds. Optionally, lithium cobalt oxide includes LiCoO _2. Lithium nickel oxide includes LiNiO _2. Lithium manganese oxide includes at least one of LiMnO ₂ and LiMn ₂ O ₄ . Lithium nickel cobalt manganese oxide includes at least one of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM ₆₂₂ ), and LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM ₈₁₁ ). Lithium nickel cobalt aluminum oxide includes LiNi _0.85 Co _0.15 Al _0.05 O _2. Examples of lithium-containing phosphates of olivine structure may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Optionally, the lithium iron phosphate includes LiFePO ₄ (LFP). The lithium manganese phosphate includes LiMnPO ₄ .

In some embodiments, when the secondary battery is a sodium ion battery, the positive electrode active material may be a positive electrode active material for sodium ion batteries known in the art. As an example, the positive electrode active material may be used alone or in combination of two or more. Among them, the positive electrode active material may be selected from 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 nickel iron manganese composite oxide, Prussian blue materials, polyanion materials, etc., but the present application is not limited to these materials, and the present application may also use other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries. Optionally, the sodium iron composite oxide includes NaFeO _2. The sodium cobalt composite oxide includes NaCoO _2. The sodium chromium composite oxide includes NaCrO _2. The sodium manganese composite oxide includes NaMnO _2. The sodium nickel composite oxide includes NaNiO ₂ . The sodium nickel titanium composite oxide includes NaNi _1/2 Ti _{1/2 O 2.} The sodium nickel manganese composite oxide includes NaNi _1/2 Mn _1/2 O _2. The sodium iron manganese composite oxide includes Na _2/3 Fe _1/3 Mn _2/3 O _2. The sodium nickel cobalt manganese composite oxide includes NaNi _1/3 Co _1/3 Mn _1/3 O _2. The sodium iron phosphate includes NaFePO _4. The sodium manganese phosphate includes NaMnPO _4. The sodium cobalt phosphate includes NaCoPO _4. The polyanion material includes at least one of phosphate, fluorophosphate, pyrophosphate and sulfate.

In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet can be obtained after drying, cold pressing and other processes. Optionally, the solvent includes N-methylpyrrolidone.

[Negative electrode]

The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate. Optionally, the metal material includes at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. The polymer material includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), polyamide-imide (PAI), polyethyleneimine (PEI), polyimide (PI), and polytert-butyl acrylate-triethoxyvinylsilane (TBATEVS).

In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may further include other additives, such as a thickener. Optionally, the thickener includes sodium carboxymethyl cellulose (CMC-Na).

In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and the negative electrode sheet can be obtained after drying, cold pressing and other processes. Optionally, the solvent includes deionized water.

[Electrolytes]

The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

In some embodiments, the electrolyte is an electrolytic solution.

In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[Isolation film]

In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG1 is a secondary battery 1 of a square structure as an example. It is understood that the secondary battery 1 may be a sodium ion battery.

In some embodiments, referring to FIG. 2 , the outer package may include a shell 11 and a top cover assembly 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the top cover assembly 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

In addition, the present application also provides an electrical device, which includes a secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto. For example, mobile devices include mobile phones, laptop computers, etc. Electric vehicles include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

As the electrical device, a secondary battery can be selected according to its usage requirements.

Fig. 3 shows an electric device 2 as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

Example

Example 1

In this embodiment, the electrolyte includes a sodium salt containing S, a sodium salt containing B, and a solvent, wherein the sodium salt containing S is sodium bis(fluorosulfonyl)imide (NaFSI), and the sodium salt containing B is sodium difluorooxalate borate (NaDFOB). In the electrolyte, the molar concentration of the sodium salt containing S is 0.5 mol/L, the molar concentration of the sodium salt containing B is 0.2 mol/L, and the molar ratio of the S element to the B element is 5:1. The solvent is a mixed solvent of propylene carbonate (PC) and dimethyl carbonate (DMC) in a volume ratio of 1:1.

Embodiments 2 to 11

Compared with Example 1, the difference between Examples 2 to 4 is that in the electrolyte, one or more of the molar concentration of the sodium salt containing S, the molar concentration of the sodium salt containing B, and the corresponding molar ratio of the S element to the B element are different. Specifically, as shown in Table 1.

Embodiment 12-13

Compared with Example 2, the difference between Examples 12 and 13 is that the solvents in the electrolyte are different.

Embodiment 14

In this embodiment, the electrolyte includes a sodium salt containing S, a sodium salt containing B, an additive and a solvent, wherein the sodium salt containing S is sodium bis(fluorosulfonyl)imide (NaFSI), and the sodium salt containing B is sodium difluorooxalate borate (NaDFOB). In the electrolyte, the molar concentration of the sodium salt containing S is 0.5 mol/L, the molar concentration of the sodium salt containing B is 0.2 mol/L, and the molar ratio of the S element to the B element is 5:1. The solvent is a mixed solvent of propylene carbonate and dimethyl carbonate in a volume ratio of 1:1. The additive is sodium poly(disulfide dipropane sulfonate), and the molar concentration of the additive in the electrolyte is 0.003 mol/L.

Embodiments 15 to 33

Compared with Example 14, the difference between Examples 15 to 33 is that one or more of the molar concentration of the sodium salt containing S, the molar concentration of the sodium salt containing B, the molar ratio of the S element to the B element, the additive and its molar concentration, and the type of solvent are different. The details are shown in Table 1.

Comparative Example 1~2

Compared with Example 1, the difference between Comparative Examples 1 and 2 is that the molar concentration of the S sodium salt, the molar concentration of the B sodium salt, and the molar ratio of the S element to the B element are different.

Comparative Examples 3~4

Compared with Example 14, the difference between Comparative Examples 3 and 4 is that the molar concentration of the S sodium salt, the molar concentration of the B sodium salt, and the molar ratio of the S element to the B element are different.

Comparative Example 5

Compared with Example 1, the difference of Comparative Example 5 is that the sodium salt containing S in the electrolyte is replaced by a sodium salt containing B in an equimolar concentration.

Comparative Example 6

Compared with Example 1, the difference of Comparative Example 6 is that the sodium salt containing B in the electrolyte is replaced by a sodium salt containing S in an equimolar concentration.

Comparative Example 7

Compared with Example 14, the difference in Comparative Example 7 is that the sodium salt containing S in the electrolyte is replaced by a sodium salt containing B in an equimolar concentration.

Comparative Example 8

Compared with Example 14, the difference in Comparative Example 8 is that the sodium salt containing B in the electrolyte is replaced by a sodium salt containing S in an equimolar concentration.

Comparative Example 9

Compared with Example 1, the difference of Comparative Example 9 is that the S-containing sodium salt and the B-containing sodium salt in the electrolyte are replaced by sodium hexafluorophosphate with equimolar concentrations.

Comparative Example 10

Compared with Example 11, the difference of Comparative Example 10 is that the S-containing sodium salt and the B-containing sodium salt in the electrolyte are replaced by sodium hexafluorophosphate with equimolar concentrations.

In Table 1, the unit of molar concentration is mol/L, which represents the molar concentration in the electrolyte.

Test Case

(1) Preparation of positive electrode.

10wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and 10wt% carbon black conductive agent and 80wt% sodium nickel iron manganese oxide positive electrode active material were added to prepare a uniformly dispersed slurry. The slurry was evenly coated on the surface of 60μm aluminum foil, and then transferred to a vacuum drying oven for complete drying. The obtained pole piece was rolled and then punched to obtain a positive pole piece.

(2) Preparation of negative electrode sheets.

The negative electrode active material hard carbon, the conductive agent acetylene black, the binder SBR and the thickener CMC-Na were dissolved in deionized water in a weight ratio of 94:2:2.8:1.2, and stirred evenly to form a negative electrode slurry. The slurry was prepared after ultrasonic dispersion, and then coated on the surface of a 12μm copper foil, and then transferred to a vacuum drying oven for complete drying to prepare a negative electrode sheet.

(3) Preparation of electrolyte.

In an argon atmosphere glove box with H ₂ O<0.1 ppm and O ₂ <0.1 ppm, the raw materials for preparing the electrolyte in the example and the comparative example were mixed and stirred evenly to prepare an electrolyte.

(4) Isolation film.

Polypropylene film is used as the isolation film.

(5) Preparation of sodium ion batteries.

The positive electrode sheet in (1), the separator in (4), and the negative electrode sheet in (2) are stacked in order, with the separator being located between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrolyte in (3) is added to assemble a stacked battery.

(6) Storage capacity retention rate test.

The sodium ion battery prepared in (5) was charged to 4V at a constant current of 0.2C at 25°C, then charged at a constant voltage of 4V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.2C to obtain the discharge capacity before storage (Cd1); then the battery was charged to 4V at a constant current of 0.2C again, and then charged at a constant voltage of 4V until the current dropped to 0.05C. The battery was then stored in a 60°C constant temperature box for 30 days. After being taken out, the battery was placed at 25°C and charged to 4V at a constant current of 0.2C, then charged at a constant voltage of 4V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.2C to obtain the discharge capacity after storage (Cd2), and the capacity retention rate of the sodium ion battery was calculated according to the following formula:

Storage capacity retention rate = discharge capacity after storage (Cd2) / discharge capacity before storage (Cd1) × 100%. The results are shown in Table 1.

(7) Cycle capacity retention rate.

The sodium ion battery prepared in (5) was charged to 3.7V at a constant current of 0.2C at 25°C, then charged at a constant voltage of 3.7V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 0.2C to obtain the first cycle discharge capacity (Cd3); this charging and discharging was repeated until the nth cycle, and the discharge capacity of the sodium ion battery after n cycles was obtained, which was recorded as Cdn, and the capacity retention rate of the sodium ion battery was calculated according to the following formula:

Cycle capacity retention rate = discharge capacity after n cycles (Cdn) / first cycle discharge capacity (Cd3). The cycle capacity retention rate after 20 cycles is shown in Table 1.

In Table 1, NaFSI represents sodium bis(trifluoromethylsulfonyl)imide, NaTFSI represents sodium bis(trifluoromethylsulfonyl)imide, NaDFOB represents sodium difluorooxalatoborate, and _NaBF4 represents sodium tetrafluoroborate.

Table 1

It is understandable that, since the additive may also contain a certain amount of S element, in the electrolyte, when the additive is present, the content of S element may be slightly higher than the content of S element in the electrolyte without the additive.

It can be seen from Examples 1 to 33 and Comparative Examples 5 to 8 in Table 1 that when the electrolyte contains both S and B elements, the corresponding sodium ion battery exhibits better storage capacity retention and cycle capacity retention. It can be seen from Examples 1 to 33 and Comparative Examples 1 to 4 that when the electrolyte contains both S and B elements, and the molar ratio of S and B elements is (2 to 20): 1, the corresponding sodium ion battery exhibits better storage capacity retention and cycle capacity retention. It can be seen from Examples 28 to 30 that when the electrolyte contains additives, the storage capacity retention and cycle capacity retention of the corresponding sodium ion battery are better, and when the molar concentration of the additive is 0.001 mol/L to 0.015 mol/L, the corresponding sodium ion battery exhibits better storage capacity retention and cycle capacity retention.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims (15)

1. An electrolyte, characterized in that it includes S-containing anions and B-containing anions, and the S-containing anions include at least one of N(FSO ₂ ) ₂ ^- and N(CF ₃ SO ₂ ) ₂ ^- , the The B-containing anion includes at least one of B(F ₂ C ₂ O ₄ ) ^- and BF ₄ ^- , and the molar ratio of S element to B element in the electrolyte is (2~20):1; the electrolytic Liquid contains F elements and N elements. 2. The electrolytic solution according to claim 1, characterized in that, in the electrolytic solution, the molar concentration of element S is 1mol/L˜4mol/L. 3. The electrolytic solution according to claim 1, characterized in that, in the electrolytic solution, the molar concentration of element B is 0.1mol/L˜1mol/L. 4 . The electrolyte solution according to claim 1 , wherein the molar ratio of element F to element N is (2.2-10):1. 5. The electrolytic solution according to claim 4, characterized in that, in the electrolytic solution, the molar concentration of element F is 1.4mol/L˜6.8mol/L. 6. The electrolytic solution according to claim 4, characterized in that, in the electrolytic solution, the molar concentration of N element is 0.5 mol/L-2 mol/L. 7. The electrolytic solution according to any one of claims 1 to 6, characterized in that it comprises sodium salt containing S and sodium salt containing B. 8. The electrolytic solution according to claim 7, wherein the sodium salt containing S comprises at least one of sodium bisfluorosulfonyl imide and sodium bis(trifluoromethylsulfonyl)imide. 9. The electrolytic solution according to claim 7, wherein the B-containing sodium salt comprises at least one of sodium difluorooxalate borate and sodium tetrafluoroborate. 10. The electrolytic solution according to claim 7, further comprising an additive comprising an alkyl sodium salt. 11. The electrolytic solution according to claim 10, wherein the alkyl sodium salt comprises at least one of sodium lauryl sulfate and sodium polydithiodipropane sulfonate. 12. The electrolyte solution according to claim 10, characterized in that the molar concentration of the additive is 0.001mol/L˜0.015mol/L. 13. The electrolytic solution according to claim 1, wherein the solvent in the electrolytic solution comprises ethylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate Ester, ethyl acetate, ethyl propionate, methyl propionate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether At least one of alcohol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, tetrahydrofuran and methyl tetrahydrofuran. 14. A sodium ion battery, characterized in that it comprises the electrolyte solution according to any one of claims 1 to 13. 15. An electric device, characterized in that it comprises the sodium ion battery according to claim 14.