Sodium ion battery, energy storage device and energy storage system

Abstract

The invention provides a sodium ion battery, an energy storage device and an energy storage system. The sodium ion battery comprises a positive pole piece, a diaphragm, a negative pole piece and an electrolyte, the negative pole piece comprises a carbon material, the specific surface area of the carbon material is x, the carbon material comprises mesopores, the number percentage of the mesopores in the carbon material is y, and the electrolyte comprises an organic solvent, an electrolyte salt, an organic additive and a sodium salt additive, the organic solvent comprises cyclic carbonate and chain carbonate, the mass fraction of the cyclic carbonate in the electrolyte is a, the mass fraction of the chain carbonate in the electrolyte is b, the mass fraction of the organic additive in the electrolyte is c, and the mass fraction of the sodium salt additive in the electrolyte is d; the sodium ion battery meets the relational expression of 0.4 < = a / y < = 0.8; 0.5 < = a / b < = 1.3; 0.4 < = c / x < = 1.2; and 0.1 < = d / c < = 0.5.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and specifically to a sodium ion battery, an energy storage device, and an energy storage system. Background Art

[0002] The growing popularity of electric vehicles has led to a surge in global demand for lithium-ion batteries. However, limited lithium supply, uneven geographical distribution, and high prices have raised concerns about the sustainable supply of lithium. Sodium-ion batteries offer a promising alternative due to their abundant resources, low cost, and excellent safety. However, existing sodium-ion batteries struggle to achieve both a high cycle life and long storage capacity retention. Summary of the Invention

[0003] The embodiments of the present application provide a sodium ion battery having high cycle performance and storage performance.

[0004] In a first aspect, an embodiment of the present application provides a sodium ion battery, the sodium ion battery comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, the negative electrode sheet comprising a carbon material, the specific surface area of ​​the carbon material is x, in units of m2 / g, the carbon material comprises mesopores, and the number percentage of the mesopores in the carbon material is y, in units of %; the electrolyte comprises an organic solvent, an electrolyte salt, an organic additive and a sodium salt additive, the organic solvent comprises a cyclic carbonate and a chain carbonate, the mass fraction of the cyclic carbonate in the electrolyte is a, in units of %, the mass fraction of the chain carbonate in the electrolyte is b, in units of %; the mass fraction of the organic additive in the electrolyte is c, in units of %, and the mass fraction of the sodium salt additive in the electrolyte is d, in units of %;

[0005] The sodium ion battery satisfies the relationship:

[0006] 0.4≤a / y≤0.8;

[0007] 0.5≤a / b≤1.3;

[0008] 0.4≤c / x≤1.2; and

[0009] 0.1≤d / c≤0.5.

[0010] Furthermore, the percentage of the mesopores in the carbon material ranges from 50% to 70%.

[0011] Furthermore, the carbon material further includes macropores and micropores. The percentage of the macropores in the carbon material is in a range of 30% to 40%, and the percentage of the micropores in the carbon material is in a range of 1% to 5%.

[0012] Furthermore, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate; and the mass fraction of the cyclic carbonate in the electrolyte ranges from 29% to 45%.

[0013] Furthermore, the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and the mass fraction of the chain carbonate in the electrolyte ranges from 35% to 51%.

[0014] Furthermore, the carbon material includes hard carbon, and the specific surface area of ​​the carbon material ranges from 3 m2 / g to 7 m2 / g.

[0015] Furthermore, the organic additive includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, and tris(trimethylsilyl)phosphate; the mass fraction of the organic additive in the electrolyte ranges from 2% to 5%.

[0016] Furthermore, the sodium salt additive includes at least one of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorooxalatoborate, sodium bis(oxalato)borate, sodium tetrafluoroborate, sodium difluorophosphate and sodium difluorobis(oxalatophosphate); the mass fraction of the sodium salt additive in the electrolyte ranges from 0.5% to 1.5%.

[0017] In a second aspect, an embodiment of the present application further provides an energy storage device, comprising:

[0018] cabinet; and

[0019] The sodium ion battery described in the embodiment of the first aspect of the present application is accommodated in the box.

[0020] In a third aspect, an embodiment of the present application further provides an energy storage system, comprising:

[0021] The energy storage device according to the second aspect of this application; and

[0022] An electric energy conversion device, the electric energy conversion device is electrically connected to the energy storage device, the electric energy conversion device is used to convert other forms of energy into electric energy, and the energy storage device is used to store the electric energy.

[0023] This application can effectively reduce the electrolyte consumption and gas production of sodium-ion batteries during circulation and storage, and improve the circulation and storage capacity retention rate of sodium-ion batteries by regulating the composition of organic solvents, organic additives and sodium salt additives in the electrolyte and the specific surface area and mesopore ratio of the negative electrode active material. When the mass ratio of cyclic carbonates and chain carbonates in the electrolyte satisfies 0.5≤a / b≤1.3, the electrolyte has high conductivity, low viscosity and a wide liquid range, which can take into account the high and low temperature performance of sodium-ion batteries; when the numerical ratio of the mass fraction of cyclic carbonates in the electrolyte to the number percentage of mesopores in the carbon material satisfies 0.4≤a / y≤0.8, it can balance the interfacial contact between the electrolyte and the internal pores and the diffusion capacity of sodium ions during the charge and discharge process. When the numerical ratio of the mass fraction of the organic additive in the electrolyte and the specific surface area of ​​the carbon material satisfies 0.4≤c / x≤1.2, and the numerical ratio of the mass fraction of the sodium salt additive and the organic additive in the electrolyte satisfies 0.1≤d / c≤0.5, the solvent molecules of the organic additive and the anions of the sodium salt additive preferentially enter the solvated inner layer, forming a layer of organic-inorganic solid electrolyte interface (SEI) film with high ionic conductivity and low solubility on the surface / pores of the negative electrode active material, isolating the reaction between the electrolyte and the negative electrode sheet, reducing the specific surface area of ​​the negative electrode active material, forming a large number of closed nanopores, and filling more sodium clusters into the closed nanopores, which is beneficial to the storage of sodium ions in the low-pressure platform area, thereby greatly improving the storage capacity retention rate of the sodium ion battery. In summary, the present application regulates the specific surface area and mesopore ratio of cyclic carbonates, chain carbonates, organic additives, sodium salt additives, carbon materials in the electrolyte of sodium ion batteries, thereby regulating the desolvation ability of the electrolyte, constructing a low-solubility, high-stability SEI film, reducing the gas production of sodium ion batteries during storage / cycling, inhibiting electrolyte consumption, and improving the calendar life and cycle life of sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 Schematic diagram of the structure of a sodium battery according to an embodiment of the present application.

[0026] Figure 2 This is a sodium battery according to an embodiment of the present application. Figure 1 Schematic diagram of the cross-sectional structure in the AA direction.

[0027] Figure 3 It is a structural schematic diagram of the positive electrode plate of an embodiment of the present application.

[0028] Figure 4 Schematic diagram of the structure of the negative electrode sheet of one embodiment of the present application.

[0029] Figure 5 It is the XPS graph of the negative electrode sheet of the sodium ion battery after formation of Example 3 and Comparative Example 4.

[0030] Figure 6 It is a structural diagram of an energy storage device according to an embodiment of the present application.

[0031] Figure 7 This is a structural block diagram of an energy storage system according to an embodiment of the present application.

[0032] Figure 8 This is an application scenario diagram of the energy storage system of one embodiment of the present application.

[0033] Description of reference numerals:

[0034] 100-sodium ion battery, 110-positive electrode plate, 111-positive electrode current collector, 112-positive electrode active layer, 120-diaphragm, 130-negative electrode plate, 131-negative electrode current collector, 132-negative electrode active layer, 140-housing, 141-receiving chamber, 150-end cover assembly, 200-energy storage device, 210-box, 300-energy storage system, 310-electric energy conversion device. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0036] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0037] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0038] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0039] Currently, the generation of green electricity generally relies on photovoltaics, wind power, and hydropower. However, wind and solar energy are generally intermittent and highly volatile, which can cause grid instability, insufficient electricity during peak hours, and excessive electricity during off-peak hours. Unstable voltage can also damage electricity. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar power curtailment". To solve these problems, we must rely on energy storage. This means converting electrical energy into other forms of energy through physical or chemical means and storing them. When needed, this energy is converted into electrical energy and released. Simply put, energy storage is like a large "power bank", storing electricity when photovoltaic and wind energy are sufficient and releasing the stored electricity when needed.

[0040] Batteries are the smallest energy storage unit in energy storage devices and systems. Their performance directly impacts the performance and applications of these devices and systems. Batteries include lithium batteries (such as lithium-ion batteries) and sodium batteries (such as sodium-ion batteries).

[0041] The growing popularity of electric vehicles has led to a surge in global demand for lithium-ion batteries. However, limited lithium supply, uneven geographical distribution, and high prices have raised concerns about the sustainable supply of lithium. Sodium-ion batteries offer a promising alternative due to their abundant resources, low cost, and excellent safety. However, existing sodium-ion batteries struggle to achieve both high cycle life and high storage capacity retention.

[0042] See Figure 1 and Figure 2 An embodiment of the present application provides a sodium ion battery 100 , which includes a positive electrode sheet 110 , a separator 120 , a negative electrode sheet 130 , and an electrolyte.

[0043] Optionally, the sodium-ion battery 100 may be, but is not limited to, at least one of a cylindrical battery, a square battery, a blade battery, etc. The drawings in this application illustrate only one or more possible forms of the sodium-ion battery 100 and should not be construed as limiting the sodium-ion battery 100 of the embodiments of this application.

[0044] It can be understood that the positive electrode sheet 110 and the negative electrode sheet 130 are respectively located on opposite sides of the separator 120 , that is, the separator 120 is located between the positive electrode sheet 110 and the negative electrode sheet 130 to separate the positive electrode sheet 110 from the negative electrode sheet 130 .

[0045] Optionally, the positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 are stacked in sequence to form an electrode assembly, which is then wound as a whole to form a bare cell. It should be noted that the positive electrode sheet 110 and the negative electrode sheet 130 can be collectively referred to as electrode sheets. In other words, the electrode sheet includes the positive electrode sheet 110 and the negative electrode sheet 130.

[0046] It should be noted that the positive electrode sheet 110 , the separator 120 and the negative electrode sheet 130 are at least partially immersed in the electrolyte.

[0047] See Figure 3 The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 . The positive electrode active layer 112 is disposed on the surface of the positive electrode current collector 111 .

[0048] It should be noted that the positive electrode active layer 112 can be provided on one surface of the positive electrode current collector 111, or on two opposite surfaces of the positive electrode current collector 111. In the following embodiments and accompanying drawings of the present application, the positive electrode sheet 110 is described and illustrated as including two layers of positive electrode active layers 112 (i.e., the positive electrode active layers 112 are provided on two opposite surfaces of the positive electrode current collector 111). This should not be construed as limiting the positive electrode sheet 110 of the embodiments of the present application.

[0049] Optionally, the material of the positive electrode current collector 111 may be, but is not limited to, aluminum foil, aluminum sheet, and the like.

[0050] Optionally, the positive electrode active layer 112 includes a positive electrode active material, a positive electrode conductor, a positive electrode binder, and a positive electrode thickener.

[0051] Optionally, the positive electrode active material may be, but is not limited to, at least one of a transition metal oxide, a Prussian blue analog, and a polyanionic compound. Optionally, the transition metal oxide may be, but is not limited to, at least one of NaCoO2, NaMnO2, and NaFeO2. Optionally, the Prussian blue analog may be, but is not limited to, at least one of Na2Mn(Fe(CN)6, NaFeFe(CN)6). The polyanionic compound may be, but is not limited to, sodium ferric phosphate pyrophosphate (Na4Fe3(PO4)2P2O7, abbreviated as NFPP).

[0052] Optionally, the positive electrode conductive agent may be, but is not limited to, at least one of conductive carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0053] Optionally, the positive electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0054] Optionally, the positive electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethacrylate (PMA).

[0055] Optionally, the diaphragm 120 may be, but is not limited to, at least one of a polypropylene film (PP film for short), a polyethylene film (PE film for short), a ceramic diaphragm 120 , and the like.

[0056] See Figure 4 Optionally, the negative electrode sheet 130 includes a negative electrode current collector 131 and a negative electrode active layer 132, and the negative electrode active layer 132 is disposed on the surface of the negative electrode current collector 131. It can be understood that the negative electrode active layer 132 can cover one surface or two opposite surfaces of the negative electrode current collector 131.

[0057] Optionally, the negative electrode current collector 131 may be, but is not limited to, at least one of a copper sheet, a copper foil, and the like.

[0058] Optionally, the negative electrode active layer 132 includes a negative electrode active material, a negative electrode conductor, a negative electrode binder, and a negative electrode thickener.

[0059] Alternatively, the negative electrode active material may be, but is not limited to, a carbon material. Alternatively, the carbon material may be, but is not limited to, hard carbon.

[0060] Optionally, the negative electrode conductive agent may be, but is not limited to, at least one of conductive carbon black (SP for short), acetylene black, carbon nanotubes, carbon fibers, graphene, and the like.

[0061] Optionally, the negative electrode binder may be, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), polyhexafluoropropylene, and styrene butadiene rubber (SBR).

[0062] Optionally, the negative electrode thickener may be, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), and polymethacrylate (PMA).

[0063] In some embodiments, the specific surface area of ​​the carbon material is x, in units of m2 / g, the carbon material includes mesopores, and the number percentage of the mesopores in the carbon material is y, in units of %; the electrolyte includes an organic solvent, an electrolyte salt, an organic additive and a sodium salt additive, the organic solvent includes a cyclic carbonate and a chain carbonate, the mass fraction of the cyclic carbonate in the electrolyte is a, in units of %, the mass fraction of the chain carbonate in the electrolyte is b, in units of %; the mass fraction of the organic additive in the electrolyte is c, in units of %, and the mass fraction of the sodium salt additive in the electrolyte is d, in units of %; the sodium ion battery 100 satisfies the relationship: 0.4≤a / y≤0.8.

[0064] “Mesopores” refer to pores with a pore diameter between 2 nm and 50 nm, also known as mesopores.

[0065] Optionally, the electrolyte salt may be a sodium salt. Optionally, the sodium salt may include, but is not limited to, at least one of sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide. The molar concentration of the sodium salt in the electrolyte ranges from 0.5 mol / L to 1.2 mol / L. Specifically, the molar concentration of the sodium salt in the electrolyte may be, but is not limited to, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, and the like. If the molar concentration of the sodium salt in the electrolyte is too low, the conductivity of the electrolyte is reduced, thereby reducing the kinetic performance of the sodium ion battery 100; if the molar concentration of the sodium salt in the electrolyte is too high, a portion of the electrolyte salt is likely to remain undissociated, and the viscosity of the electrolyte is increased, which in turn reduces the conductivity of the electrolyte and also reduces the kinetic performance of the sodium ion battery 100. When the molar concentration of the sodium salt in the electrolyte is in the range of 0.5 mol / L to 1.2 mol / L, the electrolyte can have a higher electrical conductivity, thereby enabling the sodium ion battery 100 to have better kinetic performance.

[0066] In the embodiments of the present application, when a numerical value range from a to b is involved, unless otherwise specified, it means that the numerical value can be any numerical value between a and b, including the endpoint numerical value a and the endpoint numerical value b.

[0067] It can be understood that the ratio of the mass fraction a of the cyclic carbonate in the electrolyte to the number percentage y of the mesopores in the carbon material ranges from 0.4 to 0.8.

[0068] Specifically, the value of a / y can be, but is not limited to, 0.4, 0.43, 0.45, 0.48, 0.5, 0.53, 0.55, 0.58, 0.6, 0.63, 0.65, 0.68, 0.7, 0.73, 0.75, 0.78, 0.8, etc. If the value of a / y is too small, the mass fraction of the cyclic carbonate in the electrolyte is too low or the percentage of the number of mesopores in the carbon material is too high; if the mass fraction of the cyclic carbonate in the electrolyte is too low, the solubility of the electrolyte salt is limited, the electrolyte conductivity is low, and the kinetic performance and rate performance of the sodium ion battery 100 are reduced; if the proportion of mesopores in the carbon material is too high, the permeability of the solvated sodium ions and the electrolyte is enhanced, the degree of reaction between the electrolyte and the negative electrode sheet 130 is increased, the consumption of the electrolyte is increased, and the cycle performance of the sodium ion battery 100 is reduced. If the value of a / y is too large, the mass fraction of the cyclic carbonate in the electrolyte is too high or the percentage of the number of mesopores in the carbon material is too low; when the mass fraction of the cyclic carbonate in the electrolyte is too high, the viscosity of the electrolyte is too high, and the low-temperature performance and rate performance of the sodium-ion battery 100 will both deteriorate; when the percentage of the number of mesopores in the carbon material is too low, the diffusion rate of sodium ions is reduced, and the storage reversibility of the sodium-ion battery 100 is reduced. When the ratio of the mass fraction a of the cyclic carbonate in the electrolyte to the percentage of the number of mesopores y in the carbon material is in the range of 0.4 to 0.8, the interfacial contact between the electrolyte and the internal pores of the carbon material and the diffusion capacity of sodium ions during the charge and discharge process can be better balanced.

[0069] In some embodiments, the sodium ion battery 100 further satisfies the relationship: 0.5≤a / b≤1.3.

[0070] It can be understood that the ratio of the mass fraction a of the cyclic carbonate in the electrolyte to the mass fraction b of the chain carbonate in the electrolyte ranges from 0.5 to 1.3.

[0071] Specifically, the value of a / b can be, but is not limited to, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, etc. If the value of a / b is too small, the mass fraction of the cyclic carbonate in the electrolyte is too low or the mass fraction of the chain carbonate in the electrolyte is too high, the conductivity of the electrolyte is too low, and the kinetic performance of the sodium ion battery 100 is reduced. If the value of a / b is too large, the mass fraction of the cyclic carbonate in the electrolyte is too high or the mass fraction of the chain carbonate in the electrolyte is too low, the viscosity of the electrolyte is too high, the ionic conductivity of the electrolyte is reduced, and the rate performance and low-temperature performance of the sodium ion battery 100 are reduced. When the ratio of the mass fraction a of the cyclic carbonate in the electrolyte to the mass fraction b of the chain carbonate in the electrolyte is in the range of 0.5 to 1.3, the electrolyte has high conductivity, low viscosity and a wide liquid range, which can better balance the high and low temperature performance of the sodium ion battery 100.

[0072] In some embodiments, the sodium ion battery 100 further satisfies the relationship: 0.4≤c / x≤1.2.

[0073] It can be understood that the ratio of the mass fraction c of the organic additive in the electrolyte to the specific surface area x of the carbon material ranges from 0.4 to 1.2.

[0074] Specifically, the value of c / x can be, but is not limited to, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc. If the value of c / x is too small, the mass fraction of the organic additive in the electrolyte is too low or the specific surface area x of the carbon material is too large; if the mass fraction of the organic additive in the electrolyte is too low, the formed solid electrolyte interface (SEI film) is loose and porous, the water removal and acid suppression effect is poor, the internal resistance of the sodium ion battery 100 increases, the gas production increases, the storage performance of the sodium ion battery 100 is reduced, and the cycle performance of the sodium ion battery 100 is deteriorated; if the specific surface area x of the carbon material is too large, the number of active sites and defects in the carbon material is too large, and a large amount of sodium ions will be consumed during the formation of the SEI film of the sodium ion battery 100, resulting in irreversible capacity loss of the active sodium provided by the positive electrode sheet 110, thereby reducing the first coulombic efficiency and cycle stability of the sodium ion battery 100. When the value of c / x is too large, the mass fraction of the organic additive in the electrolyte is too high or the specific surface area x of the carbon material is too low; if the mass fraction of the organic additive in the electrolyte is too high, the thickness of the SEI film of the sodium ion battery 100 increases, the impedance of the sodium ion battery 100 increases, the sodium ion transmission efficiency decreases, the rate performance and low-temperature performance deteriorate, and the first coulombic efficiency decreases. In addition, if the mass fraction of the organic additive in the electrolyte is too high, the organic additive is sensitive to temperature and easily decomposes at high temperatures, thereby increasing side reactions and increasing gas production; if the specific surface area x of the carbon material is too low, the reaction sites and ion diffusion channels of the carbon material are limited, which is not conducive to the reversible intercalation and deintercalation of sodium ions.

[0075] In some embodiments, the sodium ion battery 100 further satisfies the relationship: 0.1≤d / c≤0.5.

[0076] It can be understood that the ratio of the mass fraction d of the sodium salt additive in the electrolyte to the mass fraction c of the organic additive in the electrolyte is in a range of 0.1 to 0.5.

[0077] Specifically, the value of d / c can be, but is not limited to, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc. If the value of d / c is too low, the mass fraction d of the sodium salt additive in the electrolyte is too small or the mass fraction c of the organic additive in the electrolyte is too large. When the mass fraction d of the sodium salt additive in the electrolyte is too small, solvent molecules enter the solvation shell to participate in the formation of a loose macroporous SEI film. The SEI film continuously dissolves and reorganizes during storage / circulation, accelerating the consumption of the electrolyte. If the mass fraction c of the organic additive in the electrolyte is too large, the thickness of the SEI film of the sodium ion battery 100 increases, the impedance of the sodium ion battery 100 increases, the rate performance and low-temperature performance deteriorate, and the first coulombic efficiency decreases. If the value of d / c is too high, the mass fraction d of the sodium salt additive in the electrolyte is too large or the mass fraction c of the organic additive in the electrolyte is too small. If the mass fraction d of the sodium salt additive in the electrolyte is too large, the solubility of the sodium salt additive in the electrolyte is limited, and the impedance of the sodium ion battery 100 is increased, thereby deteriorating the rate performance and low-temperature performance of the sodium ion battery 100. If the mass fraction c of the organic additive in the electrolyte is too small, the formed SEI film is loose and porous, and the water removal and acid suppression effect is poor. The internal resistance of the sodium ion battery 100 increases, the gas production increases, the storage performance of the sodium ion battery 100 is reduced, and the cycle performance of the sodium ion battery 100 is deteriorated.

[0078] The inventors have discovered that the organic additives and sodium salt additives in the electrolyte of the sodium ion battery 100 participate in the formation of the SEI film and are completely consumed in the early stages of the formation cycle / storage. The capacity retention rate of the sodium ion battery 100 during the later cycles / storage process is positively correlated with the residual amount of cyclic carbonate in the remaining electrolyte. Cyclic carbonate (especially ethylene carbonate) releases a large amount of hydrogen during the film formation process, causing volume expansion of the sodium ion battery 100, misalignment of the positive electrode sheet 110 / diaphragm 120 and the negative electrode sheet 130 / diaphragm 120, and increased polarization of the sodium ion battery 100, resulting in a reduction in the life of the sodium ion battery 100 and even causing safety issues. Increasing the mass fraction of organic additives and sodium salt additives in the electrolyte may increase the impedance of the sodium ion battery 100, reduce the first coulombic efficiency, and deteriorate the rate performance and low-temperature performance. Therefore, regulating the electrolyte solvent, the types of organic additives and sodium salt additives, and the structural parameters of the negative electrode active materials (such as carbon materials) based on the cycle / storage consumption model can optimize the SEI film composition. Reducing the side reactions of the electrolyte during the cycle / storage process is the key to improving the 100 cycle life and calendar life of sodium-ion batteries.

[0079] The term "calendar life" is used to measure the degree to which sodium-ion batteries 100 naturally age over time. Even when not in use, their capacity decreases due to chemical degradation. The industry typically uses a capacity decay of 70%-80% as the end of life.

[0080] During the research process of this application, it was found that by regulating the composition of the organic solvent, organic additives and sodium salt additives in the electrolyte and the specific surface area and mesopore ratio of the negative electrode active material, the electrolyte consumption and gas production of the sodium ion battery 100 during the cycle and storage process can be effectively reduced, and the cycle and storage capacity retention rate of the sodium ion battery 100 can be improved. When the mass ratio of cyclic carbonate to chain carbonate in the electrolyte satisfies 0.5≤a / b≤1.3, the electrolyte has high conductivity, low viscosity and a wide liquid range, which can take into account the high and low temperature performance of the sodium ion battery 100; when the numerical ratio of the mass fraction of cyclic carbonate in the electrolyte to the number percentage of mesopores in the carbon material satisfies 0.4≤a / y≤0.8, it can balance the interfacial contact between the electrolyte and the internal pores and the diffusion capacity of sodium ions during the charge and discharge process. When the numerical ratio of the mass fraction of the organic additive in the electrolyte and the specific surface area of ​​the carbon material satisfies 0.4≤c / x≤1.2, and the numerical ratio of the mass fraction of the sodium salt additive and the organic additive in the electrolyte satisfies 0.1≤d / c≤0.5, the solvent molecules of the organic additive and the anions of the sodium salt additive preferentially enter the solvated inner layer, forming an organic-inorganic SEI film with high ionic conductivity and low solubility on the surface / pores of the negative electrode active material, isolating the reaction between the electrolyte and the negative electrode plate 130, reducing the specific surface area of ​​the negative electrode active material, forming a large number of closed nanopores, and filling more sodium clusters into the closed nanopores, which is beneficial to the storage of sodium ions in the low-pressure platform area, thereby greatly improving the storage capacity retention rate of the sodium ion battery 100. In summary, the present application regulates the specific surface area and mesopore ratio of cyclic carbonates, chain carbonates, organic additives, sodium salt additives, carbon materials in the electrolyte of the sodium ion battery 100, thereby regulating the desolvation ability of the electrolyte, constructing a low-solubility, high-stability SEI film, reducing the gas production of the sodium ion battery 100 during storage / cycling, inhibiting electrolyte consumption, and improving the calendar life and cycle life of the sodium ion battery 100.

[0081] In some embodiments, the number percentage of the mesopores in the carbon material ranges from 50% to 70%.

[0082] Specifically, the percentage of the mesopores in the carbon material can be, but is not limited to, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, etc.

[0083] In this embodiment, when the percentage of mesopores in the carbon material is too low, the diffusion rate of sodium ions decreases, and the storage reversibility of the sodium ion battery 100 decreases; when the proportion of mesopores in the carbon material is too high, the permeability of solvated sodium ions and the electrolyte is enhanced, the degree of reaction between the electrolyte / negative electrode sheet 130 is increased, the consumption of the electrolyte is increased, and the cycle performance of the sodium ion battery 100 is reduced.

[0084] In some embodiments, the carbon material further includes macropores and micropores, the number percentage of the macropores in the carbon material ranges from 30% to 40%, and the number percentage of the micropores in the carbon material ranges from 1% to 5%.

[0085] "Micropores" refer to pores with a pore diameter less than 2 nm, and "macroporous" refers to pores with a pore diameter greater than 50 nm.

[0086] Specifically, the percentage of macropores in the carbon material may be, but is not limited to, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc. If the percentage of macropores in the carbon material is too high, the specific surface area of ​​the carbon material increases, and solvent molecules in the electrolyte directly enter the pores of the hard carbon and continuously react with the sodium-intercalated hard carbon, increasing side reactions of the carbon material, thereby increasing electrolyte consumption and reducing the initial coulombic efficiency of the sodium-ion battery 100.

[0087] Specifically, the percentage of the micropores in the carbon material may be, but is not limited to, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. If the percentage of the micropores in the carbon material is too small, the preparation cost of the carbon material increases; if the percentage of the micropores in the carbon material is too large, the transmission rate of the sodium ions is reduced because the micropores only allow desolvated sodium ions to enter, thereby reducing the rate performance of the sodium ion battery 100.

[0088] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate (PC). These substances can better improve the ionic conductivity of the electrolyte and better improve the stability of the SEI film of the sodium ion battery 100.

[0089] Optionally, the mass fraction of the cyclic carbonate in the electrolyte ranges from 29% to 45%.

[0090] Specifically, the mass fraction of the cyclic carbonate in the electrolyte can be, but is not limited to, 29%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 45%, etc.

[0091] In this embodiment, the electrolyte salt has limited solubility, resulting in low electrolyte conductivity, which reduces the kinetic performance and rate performance of the sodium-ion battery 100. If the mass fraction of the cyclic carbonate in the electrolyte is too high, the electrolyte viscosity will be too high, reducing the wettability of the sodium-ion battery 100 and the ion mobility, thereby reducing the rate performance and low-temperature performance of the sodium-ion battery 100.

[0092] In some embodiments, the linear carbonate includes at least one of dimethyl carbonate (EMC), diethyl carbonate (DEC), and ethyl methyl carbonate. These substances can make the electrolyte have lower viscosity and low-temperature stability.

[0093] Optionally, the mass fraction of the linear carbonate in the electrolyte ranges from 35% to 51%.

[0094] Specifically, the mass fraction of the linear carbonate in the electrolyte can be, but is not limited to, 35%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 51%, etc.

[0095] In this embodiment, if the mass fraction of the chain carbonate in the electrolyte is too low, the electrolyte viscosity is too high, reducing the ionic conductivity of the electrolyte and the rate capability and low-temperature performance of the sodium-ion battery 100. If the mass fraction of the chain carbonate in the electrolyte is too high, the electrolyte has poor thermal and electrochemical stability and is prone to decomposition at high temperatures, leading to gas generation, which in turn increases the internal pressure of the sodium-ion battery 100 and may cause expansion or safety issues.

[0096] In some embodiments, the specific surface area of ​​the carbon material ranges from 3 m2 / g to 7 m2 / g.

[0097] Specifically, the specific surface area of ​​the carbon material can be, but is not limited to, 3 m2 / g, 3.3 m2 / g, 3.5 m2 / g, 3.8 m2 / g, 4 m2 / g, 4.3 m2 / g, 4.5 m2 / g, 4.8 m2 / g, 5 m2 / g, 5.3 m2 / g, 5.5 m2 / g, 5.8 m2 / g, 6 m2 / g, 6.3 m2 / g, 6.5 m2 / g, 6.8 m2 / g, 7 m2 / g, etc.

[0098] In this embodiment, if the specific surface area x of the carbon material is too low, the reaction sites and ion diffusion channels of the carbon material are limited, which is not conducive to the reversible embedding and deintercalation of sodium ions; if the specific surface area x of the carbon material is too large, the number of active sites and defects of the carbon material is too large, and a large amount of sodium ions will be consumed during the SEI film formation process of the sodium ion battery 100, resulting in irreversible capacity loss of the active sodium provided by the positive electrode sheet 110, thereby reducing the first coulombic efficiency and cycle stability of the sodium ion battery 100.

[0099] In some embodiments, the organic additive includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfate, vinyl sulfite, and tris(trimethylsilyl) phosphate. These organic additives have a lower lowest unoccupied molecular orbital (LUMO) energy and are reduced before other electrolyte solvents. The SEI film formed by the sodium ion battery 100 is rich in organic components, so that the SEI film has better flexibility and ionic conductivity, can effectively block the transmission of electrons, inhibit further reduction and decomposition of the electrolyte, and improve the coulombic efficiency and cycle stability of the sodium ion battery 100. When the organic additive is fluoroethylene carbonate, fluoroethylene carbonate has a higher reduction potential. Fluoroethylene carbonate can decompose earlier than the organic solvent molecules to form a dense and stable interface layer (ie, SEI film) rich in NaF, inhibiting further decomposition of subsequent organic solvents, reducing active sodium loss, and improving the cycle efficiency of the sodium ion battery 100.

[0100] Optionally, the mass fraction of the organic additive in the electrolyte ranges from 2% to 5%.

[0101] Specifically, the mass fraction of the organic additive in the electrolyte may be, but is not limited to, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0102] In this embodiment, if the mass fraction of the organic additive in the electrolyte is too small, the formed SEI film is loose and porous, the water removal and acid suppression effect is poor, the internal resistance of the sodium ion battery 100 increases, the gas production increases, the storage performance of the sodium ion battery 100 is reduced, and the cycle performance of the sodium ion battery 100 is deteriorated. If the mass fraction of the organic additive in the electrolyte is too large, the thickness of the SEI film of the sodium ion battery 100 increases, the impedance of the sodium ion battery 100 increases, the rate performance and low-temperature performance of the sodium ion battery 100 deteriorate, and the first coulombic efficiency decreases.

[0103] In some embodiments, the sodium salt additive includes at least one of sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethylsulfonyl)imide, sodium difluorooxalatoborate, sodium bis(oxalato)borate, sodium tetrafluoroborate, sodium difluorophosphate, and sodium difluorobis(oxalatophosphate). These sodium salt additives have a higher reduction potential than organic additives and react with the negative active material of the negative electrode plate 130 before organic additives. In addition, these sodium salt additives can make the SEI film formed by the sodium ion battery 100 contain inorganic substances (such as sodium fluoride), thereby making the SEI film harder and denser, thereby having better mechanical strength and chemical stability, and can more effectively block direct contact between the electrolyte and the negative active material, inhibiting the occurrence of side reactions. Furthermore, the inorganic substances in the SEI film have good selective permeability to sodium ions, which can ensure the rapid transmission of sodium ions in the film and improve the charge and discharge efficiency of the sodium ion battery 100.

[0104] Optionally, the mass fraction of the sodium salt additive in the electrolyte ranges from 0.5% to 1.5%.

[0105] Specifically, the mass fraction of the sodium salt additive in the electrolyte can be, but is not limited to, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0106] In this embodiment, when the mass fraction of the sodium salt additive in the electrolyte is too small, the sodium salt additive has little effect on improving the stability of the SEI film and inhibiting gas production, causing solvent molecules to enter the solvation shell to participate in the formation of a loose macroporous SEI film. The SEI film continuously dissolves and reorganizes during storage / circulation, accelerating electrolyte consumption. When the mass fraction of the sodium salt additive in the electrolyte is too large, the sodium salt additive has limited solubility in the electrolyte, and at the same time increases the impedance of the sodium ion battery 100, deteriorating the rate performance and low-temperature performance of the sodium ion battery 100.

[0107] Please see again Figure 1 and Figure 2 Optionally, the sodium ion battery 100 further includes a shell 140 and an end cover assembly 150 , wherein the shell 140 and the end cover assembly 150 enclose a receiving cavity 141 , and the receiving cavity 141 is used to receive the electrolyte, the positive electrode sheet 110 , the diaphragm 120 and the negative electrode sheet 130 .

[0108] Optionally, the sodium ion battery 100 is charge-discharge cycled at a rate of 2P / 2P at 25° C., and a capacity retention rate after 2000 cycles is greater than or equal to 87.4%. Specifically, the capacity retention rate of the sodium ion battery 100 after 2000 cycles at a rate of 2P / 2P at 25° C. may be, but is not limited to, 87.4%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or the like.

[0109] Optionally, the sodium ion battery 100 is charged and discharged at a rate of 1P / 1P at 60°C, and the capacity retention rate after 2000 cycles is greater than or equal to 87.3%. Specifically, the capacity retention rate of the sodium ion battery 100 after 2000 cycles at a rate of 1P / 1P at 60°C may be, but is not limited to, 87.3%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc.

[0110] Optionally, the capacity retention rate of the sodium ion battery 100 after being fully charged (i.e., 100% SOC) and stored at 60° C. for 30 days (30D) is greater than or equal to 84.7%. Specifically, the capacity retention rate of the sodium ion battery 100 after being fully charged (i.e., 100% SOC) and stored at 60° C. for 30 days may be, but is not limited to, 84.7%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc.

[0111] Optionally, the gas production of the sodium ion battery 100 after being fully charged (i.e., 100% SOC) and stored at 60° C. for 30 days (30D) is less than or equal to 0.67 mL / Ah. Specifically, the gas production of the sodium ion battery 100 after being fully charged and stored at 60° C. for 30 days may be, but is not limited to, 0.67 mL / Ah, 0.6 mL / Ah, 0.55 mL / Ah, 0.5 mL / Ah, 0.45 mL / Ah, 0.4 mL / Ah, 0.35 mL / Ah, 0.3 mL / Ah, 0.25 mL / Ah, 0.2 mL / Ah, 0.15 mL / Ah, 0.1 mL / Ah, and the like.

[0112] Optionally, the first coulombic efficiency of the sodium ion battery 100 is greater than or equal to 75.3%. Specifically, the first coulombic efficiency of the sodium ion battery 100 can be, but is not limited to, 75.3%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, etc.

[0113] The sodium ion battery 100 and the electrolyte according to the embodiment of the present application are further described below through specific examples.

[0114] Examples 1 to 13, Comparative Examples 1 to 9

[0115] The preparation method of the sodium ion battery 100 of each embodiment and comparative example includes:

[0116] (1) Preparation of the positive electrode sheet 110: Sodium ferric pyrophosphate (positive electrode active material), acetylene black (positive electrode conductive agent), and polyvinylidene fluoride (positive electrode binder) are dispersed in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:1:2, and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on the aluminum foil of the positive electrode current collector 111, and after drying, cold pressing, slitting, and cutting, the positive electrode sheet 110 is obtained.

[0117] (2) Preparation of the negative electrode sheet 130: Hard carbon (carbon material, negative electrode active material), acetylene black (negative electrode conductive agent), styrene-butadiene rubber, and sodium carboxymethyl cellulose are dispersed in deionized water at a mass ratio of 95:2:2:1 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated on the copper foil of the negative electrode collector 131. After drying, cold pressing, slitting, and cutting, the negative electrode sheet 130 is obtained. The surface and mesopore percentages of the hard carbon of each embodiment and comparative example are shown in Table 1 below.

[0118] (3) Electrolyte preparation process: In an argon atmosphere glove box with a moisture content of less than or equal to 10 ppm, sodium hexafluorophosphate was dissolved in an organic solvent, and an organic additive, fluoroethylene carbonate (FEC), and a sodium salt additive, sodium bis(fluorosulfonyl)imide (NaFSI), were added to prepare an electrolyte with a sodium hexafluorophosphate mass fraction of 15.5%. The organic solvent included a cyclic carbonate and a chain carbonate, the cyclic carbonate was propylene carbonate (PC), and the chain carbonate included ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 1:1. The mass fractions of the cyclic carbonate, chain carbonate, organic additive, and sodium bis(fluorosulfonyl)imide in each embodiment and comparative example are shown in Table 1.

[0119] (4) Preparation of the separator 120 : A 16 μm polyethylene porous film was used as the separator 120 .

[0120] (5) Assembly of the sodium ion battery 100: The positive electrode sheet 110, the separator 120, and the negative electrode sheet 130 are stacked in sequence to form an electrode assembly. The electrode assembly is wound to obtain a bare cell. The middle area, top area, and bottom area of ​​the termination part (i.e., the end of the bare cell) are respectively adhered with termination tape. The cell is then placed in a polypropylene plastic outer packaging and injected with electrolyte. After vacuum packaging, standing, forming, shaping, and other processes, a soft-pack sodium ion battery 100 is obtained.

[0121] Table 1 Performance parameters of electrolyte and hard carbon of each embodiment and comparative example

[0122]

[0123]

[0124] The sodium ion batteries 100 of the above embodiments and comparative examples were subjected to the following performance tests:

[0125] (1) 25°C 2P / 2P cycle performance test: The sodium ion battery 100 is placed in a constant temperature oven at 25°C, charged to 3.3V at a constant power of 1P, and discharged to 1.5V at a constant power of 1P after standing for 10 minutes. After standing for 10 minutes, it is charged to 3.3V at a constant power of 2P, and discharged to 1.5V at a constant power of 2P after standing for 10 minutes. This cycle is repeated 2000 times, and the discharge capacities of the first and 2000 times are recorded. The capacity retention rate of the sodium ion battery 100 is calculated according to the formula: Capacity retention rate (%) = discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%.

[0126] (2) 60℃ 2P / 2P cycle performance test: The sodium ion battery 100 is placed in a constant temperature 60℃ oven and charged to 3.3V at a constant power of 1P. After standing for 10 minutes, it is discharged to 1.5V at a constant power of 1P. After standing for 10 minutes, it is charged to 3.3V at a constant power of 1P. After standing for 10 minutes, it is discharged to 1.5V at a constant power of 1P. This cycle is repeated 2000 times. The discharge capacities of the first and 2000 times are recorded. The capacity retention rate of the sodium ion battery 100 is calculated according to the formula: Capacity retention rate (%) = discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%.

[0127] (3) 60℃ 100% SOC (i.e., fully charged) storage for 30 days performance test: The sodium ion battery 100 was placed in a constant temperature oven at 25℃, discharged at a constant power of 1P to 1.5V, left to stand for 10 minutes, and then charged at a constant power of 1P to 3.3V. After standing for 10 minutes, the battery was discharged at a constant power of 1P to 1.5V. The discharge capacity was recorded as the initial discharge capacity. After standing for 10 minutes, the battery was charged at a constant power of 1P to 3.3V. The sodium ion battery 100 with 100% SOC was then placed in a constant temperature oven at 60℃, left to stand for 3 hours after 30 days. Finally, the sodium ion battery 100 was placed in a constant temperature oven at 25°C and allowed to stand for 2 hours. After that, it was discharged to 1.5V at a constant power of 1P. The discharge capacity was recorded as the discharge capacity after 30 days of storage. The capacity retention rate of the sodium ion battery 100 after 30 days of storage at 60°C was calculated according to the formula: Remaining capacity retention rate (%) = Remaining capacity / Initial capacity × 100%.

[0128] (4) Gas production after 30 days of storage at 60℃ and 100% SOC: Place the barrel containing silicone oil on an electronic balance, and hang the fully charged sodium ion battery 100 vertically on an iron stand. After the balance is reset, immerse the sodium ion battery 100 completely in the silicone oil without leaning against the wall. Record the mass at this time as the initial mass m0. Discharge the fully charged sodium ion battery 100 to 1.5V at a constant power of 0.5P. After standing for 24 hours, measure the mass m1 of the sodium ion battery 100 using the above method. According to the formula: Gas production (mL / Ah) = (m1-m0) / (ρ 硅油 × C), where C is the capacity of the sodium ion battery 100, and the gas production of the sodium ion battery 100 after storage at 60°C and 100% SOC for 30 days is calculated.

[0129] (5) First coulombic efficiency: The sodium ion battery 100 was placed in an oven at 25°C and charged to 2.8 V at a constant current of 0.1C, and the charge capacity C1 was recorded. After aging at 45°C for 24 h, the battery was charged to 3.3 V at a constant current of 0.33C, and the charge capacity C2 was recorded. After standing for 10 min, the battery was discharged to 1.5 V at a current of 0.5C, and the discharge capacity D1 was recorded. The first coulombic efficiency of the sodium ion battery 100 was calculated according to the formula: First coulombic efficiency (%) = D1 / (C1+C2)×100%.

[0130] (6) Characterization of residual amount and composition of electrolyte: The residual amount m0 ​​of sodium ion battery 100 after injection and the mass m1 of sodium ion battery 100 after different cycles were recorded, the electrolyte was centrifuged, and the electrolyte solvent composition was analyzed using Agilent 5977B single quadrupole gas chromatography-mass spectrometry system, and the sodium salt additive content in the electrolyte was analyzed using ion chromatography. The sodium ion battery 100 after cycling was soaked in dimethyl carbonate (DMC) and then dried. The mass m2 of sodium ion battery 100 was weighed, and the residual amount of electrolyte and each component was calculated according to the following formula:

[0131] Residual amount of electrolyte (%) = 100% × {1-[m0-(m1-m2)] / m0};

[0132] Residual amount of organic solvent (%) = 100% × {1-[m0 × proportion before cycle - (m1-m2) × proportion after cycle] / (m0 × proportion before cycle)};

[0133] The residual amount of sodium salt additive (%) = 100% × {1-[m0×ratio before cycle-(m1-m2)×ratio after cycle] / (m0×ratio before cycle)}.

[0134] (7) Surface chemical properties analysis: X-ray photoelectron spectroscopy (XPS) was used to analyze the surface chemical properties of the negative electrode sheet 130. The sodium ion battery 100 was disassembled in a glove box to obtain a hard carbon negative electrode sheet 130 with SEI formed on the surface. The surface of the negative electrode sheet 130 was cleaned with DMC to ensure that there was no residual electrolyte. After cleaning, the negative electrode sheet 130 was placed in a vacuum to remove the remaining solvent. The vacuum degree during the XPS test was 9.8×10 -10 The light source used was Al KA radiation, with an hv of 1486.6 eV. Calibration was performed using the peak at C1s = 284.6 eV, where "C" represents carbon and "1s" refers to the 1s orbital of carbon.

[0135] The test data of the sodium ion battery 100 of the above embodiments and comparative examples are shown in Table 2 below.

[0136] Table 2 Test data of sodium ion batteries 100 of various embodiments and comparative examples

[0137]

[0138] From the test results of Examples 1 to 4 and Comparative Examples 1 to 3 in Table 2, it can be seen that when the mass fraction of the cyclic carbonate in the electrolyte increases from 30.00% to 40.00%, the cycle capacity retention rate at 25°C, the cycle capacity retention rate at 60°C, the storage capacity retention rate at 60°C, and the first coulombic efficiency of the sodium ion battery 100 all reach the optimal value, and the gas production after 30 days of storage is the lowest. When the mass fraction of the cyclic carbonate in the electrolyte is further increased, the cycle capacity retention rate at 25°C, the cycle capacity retention rate at 60°C, the storage capacity retention at 60°C, the gas production after 30 days of storage, and the first coulombic efficiency of the sodium ion battery 100 all deteriorate. When the mass fraction of the chain carbonate in the electrolyte is too high, the thermal stability and electrochemical stability of the electrolyte are poor, and it is easy to decompose in a high temperature environment, resulting in gas generation, which in turn increases the internal pressure of the sodium ion battery 100, which may cause expansion or safety problems. When the content of cyclic carbonate in the electrolyte is too high, the viscosity of the electrolyte increases, which reduces the wettability of the sodium ion battery 100 and the ion mobility, thereby reducing the rate performance and low-temperature performance of the sodium ion battery 100.

[0139] From the test results of Example 1, Example 5 to Example 7 in Table 2, it can be seen that the organic additive fluoroethylene carbonate can improve the initial coulombic efficiency and cycle and storage capacity retention of the sodium ion battery 100, and reduce the gas production during the storage process of the sodium ion battery 100. This is because fluoroethylene carbonate has a higher reduction potential and can decompose earlier than the organic solvent molecules to form a dense and stable interface layer (i.e., SEI film) rich in NaF, inhibiting the further decomposition of the subsequent organic solvent, reducing the loss of active sodium, and improving the cycle efficiency of the sodium ion battery 100. With the increase of the mass fraction of fluoroethylene carbonate in the electrolyte, the cycle capacity retention rate of the sodium ion battery 100 at 25°C, the cycle capacity retention rate at 60°C, the storage capacity retention rate at 60°C, and the initial coulombic efficiency all gradually increase and then gradually decrease. The gas production of the sodium ion battery 100 after 30 days of storage after full charge first gradually decreases and then gradually increases. When the mass fraction of fluoroethylene carbonate is too high, the impedance of the sodium ion battery 100 increases significantly and the sodium ion transmission efficiency decreases. In addition, fluoroethylene carbonate is sensitive to temperature and decomposes faster at high temperatures. Therefore, when the mass fraction of fluoroethylene carbonate is too high, gas production may occur due to increased side reactions.

[0140] From the test results of Example 1, Example 8, Example 9, Comparative Example 4 and Comparative Example 5 in Table 2, it can be seen that with the increase of the mass fraction of the sodium salt additive in the electrolyte, the cycle capacity retention rate at 25°C, the cycle capacity retention rate at 60°C, the storage capacity retention rate at 60°C and the first coulombic efficiency of the sodium ion battery 100 first gradually increase and then gradually decrease; the gas production of the sodium ion battery 100 after being fully charged and stored for 30 days gradually decreases. The introduction of the sodium salt additive NaFSI can effectively improve the cycle life of the sodium ion battery 100 and inhibit the generation of gas during storage. This is because NaFSI has high thermal stability and electrochemical stability, can occupy the sodium ion solvation inner layer, promote the formation of a stable SEI film, and reduce the side reactions of the sodium ion battery 100; in addition, NaFSI can effectively passivate sodium metal, inhibit the side reaction of the electrolyte-electrode pole piece (such as the negative pole piece 130), reduce gas production, and improve the life of the sodium ion battery 100. When the mass fraction of NaFSI in the electrolyte is too low, the effect is not significant; when the mass fraction of NaFSI is too high, the sodium salt additive participates in the film-forming reaction during the formation stage of the sodium-ion battery 100, and the first coulombic efficiency of the sodium-ion battery 100 is reduced.

[0141] From the test results of Example 1, Example 10, Example 11, Comparative Example 6 and Comparative Example 7 in Table 2, it can be seen that with the increase of the specific surface area of ​​hard carbon, the cycle capacity retention rate of the sodium ion battery 100 at 25°C gradually increases, the cycle capacity retention at 60°C first slowly increases and then gradually decreases, the storage capacity retention at 60°C first slowly increases and then gradually decreases, and the first coulombic efficiency gradually increases; the gas production of the sodium ion battery 100 after being fully charged and stored for 30 days gradually increases. By regulating the specific surface area of ​​the hard carbon, the rate performance, cycle performance, and storage performance of the sodium ion battery 100 can be taken into account without deteriorating the first coulombic efficiency of the sodium ion battery 100. This is because hard carbon with a low specific surface area can better reduce the occurrence of side reactions during the charge and discharge process, thereby improving the first coulombic efficiency of the sodium ion battery 100, but it will reduce the transmission efficiency of sodium ions; hard carbon with a high specific surface area has many active sites, which will consume a large amount of sodium ions during the SEI formation process, resulting in irreversible loss of active sodium provided by the positive electrode sheet 110, thereby affecting the first coulombic efficiency and cycle stability of the sodium ion battery 100. The test results of Comparative Examples 6 and 7 show that hard carbon with too low or too high a surface area will deteriorate the rate performance, cycle performance, and storage performance of the sodium ion battery 100.

[0142] The test results for Examples 1, 12, 13, Comparative Examples 8, and 9 in Table 2 show that as the proportion of mesopores in the hard carbon increases, the cycle capacity retention of the sodium-ion battery 100 at 25°C first increases gradually and then decreases, the cycle capacity retention at 60°C first increases slowly and then decreases gradually, the storage capacity retention at 60°C first increases slowly and then decreases gradually, and the initial coulombic efficiency gradually decreases. The gas production of the sodium-ion battery 100 after 30 days of storage after full charge first decreases and then gradually increases. Regulating the proportion of mesopores in the hard carbon can achieve superior overall performance in the sodium-ion battery 100. The ultramicroporous hard carbon allows desolvated sodium ions to enter the pores. This reduces the interfacial contact between the electrolyte and the internal pores without sacrificing the sodium ion diffusion rate, enhancing sodium ion transport during charge and discharge, and increasing the irreversible capacity. Mesopores and macropores facilitate the diffusion of solvated sodium ions and the penetration of the electrolyte, thereby shortening the diffusion distance and increasing the diffusion rate. When the number of micropores in hard carbon accounts for too much, the sodium ion transmission rate in the electrolyte decreases, and the 100-fold rate performance of the sodium ion battery deteriorates; when the number of macropores accounts for too much, the solvent molecules in the electrolyte directly enter the pores of the hard carbon and continuously react with the sodium-embedded hard carbon, deteriorating the cycle performance and storage performance of the sodium ion battery 100.

[0143] In addition, the test results of Examples 1 to 4 and Comparative Examples 1 to 3 in Table 2 show that when 0.4 ≤ a / y ≤ 0.8 and 0.5 ≤ a / b ≤ 1.3, the sodium ion battery 100 has a higher 25°C cycle capacity retention rate, 60°C cycle capacity retention rate, 60°C storage capacity retention rate, and first coulombic efficiency, and has a lower storage gas production. Excessively large or small values ​​of a / y and a / b will reduce the 25°C cycle capacity retention rate, 60°C cycle capacity retention rate, 60°C storage capacity retention rate, and first coulombic efficiency of the sodium ion battery 100, and increase the storage gas production of the sodium ion battery 100.

[0144] The test results of Examples 1, 5 to 11, Comparative Examples 4 and 6 show that when 0.4 ≤ c / x ≤ 1.2 and 0.1 ≤ d / c ≤ 0.5, the sodium ion battery 100 has a higher 25°C cycle capacity retention rate, 60°C cycle capacity retention rate, 60°C storage capacity retention rate, and first coulombic efficiency, and has a lower storage gas production. A high or low c / x value will reduce the 25°C cycle capacity retention rate, 60°C cycle capacity retention rate, 60°C storage capacity retention rate, and first coulombic efficiency of the sodium ion battery 100, and increase the storage gas production of the sodium ion battery 100.

[0145] The cycle capacity retention rate of the sodium ion battery 100 of Example 3 at different cycle times and the residual amount of each component in the electrolyte are shown in Table 3 below.

[0146] Table 3 Performance parameters of the sodium ion battery 100 of Example 3

[0147]

[0148] It can be seen from the test results in Table 3 that the electrolyte consumption of the sodium ion battery 100 in Example 3 during the formation stage is mainly due to the reaction of additives (organic additives and sodium salt additives). In the early stage of the cycle (after 10 cycles), the SEI film of the sodium ion battery 100 is unstable and will continue to form and repair. The residual organic additives and sodium salt additives are completely consumed at this stage. During the cycle from 1000 to 2000 times, the capacity decay region of the sodium ion battery 100 is stable, and there is no significant increase in the consumption of the electrolyte at this stage. Normalizing the residual amount of each substance in the electrolyte, we found that the capacity of the sodium ion battery 100 remains basically the same as the residual amount of cyclic carbonate. Therefore, optimizing the type and content of organic solvents, organic additives, and sodium salt additives in the electrolyte can effectively suppress the consumption and gas production of the electrolyte of the sodium ion battery 100 during the cycle, thereby improving the cycle life of the sodium ion battery 100.

[0149] The XPS images of the negative electrode sheet 130 after formation of the sodium ion battery 100 of Example 3 and Comparative Example 4 are as follows: Figure 5 shown. Figure 5 In the figure, C 1s represents the photoelectron spectrum peak generated by the electrons in the 1s orbit of carbon atom excited by X-rays, F 1s represents the photoelectron spectrum peak generated by the electrons in the 1s orbit of fluorine atom excited by X-rays, and O 1s represents the photoelectron spectrum peak generated by the electrons in the 1s orbit of oxygen atom excited by X-rays. Figure 5 In the C1s spectrum and F1s spectrum of the sodium fluoride battery, the peaks near 283.0 eV and 684.0 eV correspond to the responses of metal carbides and sodium fluoride, respectively. After the content of FEC and NaFSI in the electrolyte increases, the metal carbide response disappears and the sodium fluoride response is significantly enhanced, which indicates that FEC and NaFSI participate in the formation of the SEI film during the formation stage. The SEI film rich in sodium fluoride is dense and stable, which effectively inhibits the consumption of the electrolyte of the sodium ion battery 100 during the cycle and storage process, and improves the life of the sodium ion battery 100.

[0150] See Figure 6 The embodiment of the present application further provides an energy storage device 200 , which includes a box 210 and the sodium ion battery 100 described in the embodiment of the present application, wherein the sodium ion battery 100 is accommodated in the box 210 .

[0151] The energy storage device 200 of the present application can be applied to, but is not limited to, energy storage on the power generation side, energy storage on the grid side, and energy storage on the power consumption side.

[0152] Optionally, the energy storage device 200 may include, but is not limited to, a battery module, a battery pack, a battery system, an energy storage box, an energy storage cabinet, an energy storage container, and the like. The actual application form of the energy storage device 200 provided in the embodiments of the present application may be, but is not limited to, the products listed above, and may also be other application forms. The embodiments of the present application do not strictly limit the application form of the energy storage device 200. The drawings in the embodiments of the present application only illustrate an energy storage device 200 including multiple sodium-ion batteries 100 as an example, and should not be construed as limiting the energy storage device 200 in the embodiments of the present application.

[0153] Optionally, the number of sodium ion batteries 100 may be, but is not limited to, one or more. When there are multiple sodium ion batteries 100, the multiple sodium ion batteries 100 are stacked in the box 210. It is understandable that the stacking arrangement of the multiple sodium ion batteries 100 can be that the multiple sodium ion batteries 100 are arranged in sequence against each other, or the multiple sodium ion batteries 100 are arranged in sequence and spaced apart. In addition, the multiple sodium ion batteries 100 can be stacked in the transverse direction (such as the horizontal direction) or the longitudinal direction (such as the direction of gravity). The stacking method and stacking direction of the multiple sodium ion batteries 100 can be designed according to actual conditions, and this application does not impose any specific restrictions.

[0154] The term "plurality" means greater than or equal to two.

[0155] It is understandable that the multiple sodium ion batteries 100 of the energy storage device 200 can be connected in parallel with each other; or in series with each other; or partially in parallel and partially in series (in other words, mixed connection). This application does not specifically limit the connection method of the multiple sodium ion batteries 100 of the same energy storage device 200.

[0156] It is understood that the housing 210 has a receiving cavity, and one or more sodium-ion batteries 100 are received in the receiving cavity. In some embodiments, each receiving cavity receives one sodium-ion battery 100. In other embodiments, each receiving cavity receives multiple sodium-ion batteries 100.

[0157] See Figure 7 and Figure 8 , an embodiment of the present application also provides an energy storage system 300, which includes the energy storage device 200 described in the embodiment of the present application; and an electric energy conversion device 310, the electric energy conversion device 310 is electrically connected to the energy storage device 200, the electric energy conversion device 310 is used to convert other forms of energy into electric energy, and the energy storage device 200 is used to store the electric energy.

[0158] It should be noted that energy storage (i.e., energy storage) has a wide range of application scenarios, including power generation-side energy storage, grid-side energy storage, and power consumption-side energy storage. The energy storage system 300 of the embodiment of the present application is described in detail using power generation-side energy storage as an example. This should not be construed as limiting the energy storage system 300 of the embodiment of the present application, nor should it be construed as limiting the energy storage device 200, sodium-ion battery 100, and other embodiments of the present application.

[0159] During operation, the power conversion device 310 converts other forms of energy into electrical energy and stores it in the energy storage device 200. This stored energy can be used to supply loads such as streetlights and household appliances during peak electricity prices, or to provide power during power outages. The electricity generated by the power conversion device 310 can also be supplied to the grid via high-voltage cables to alleviate pressure on the grid during peak hours.

[0160] Optionally, the electric energy conversion device 310 can convert at least one other form of energy such as solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0161] Optionally, the number of the electric energy conversion devices 310 may be one or more. When there are multiple electric energy conversion devices 310, the multiple electric energy conversion devices 310 may be connected in series, in parallel, or in mixed connection, which is not specifically limited in this application.

[0162] Optionally, the electric energy conversion device 310 may be, but is not limited to, at least one of a photovoltaic panel, a wind power generation device, a hydropower generation device, and the like.

[0163] Optionally, the number of the energy storage devices 200 may be one or more. When the number of the energy storage devices 200 is multiple, the multiple energy storage devices 200 are connected in series or in parallel, which is not specifically limited in this application.

[0164] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of this application, unless there is a contradiction between them.

[0165] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A sodium ion battery, characterized in that The sodium ion battery includes a positive electrode plate, a separator, a negative electrode plate and an electrolyte, the negative electrode plate includes a carbon material, the specific surface area of ​​the carbon material is x, the unit is m2 / g, the carbon material includes mesopores, and the number percentage of the mesopores in the carbon material is y, the unit is %; the electrolyte includes an organic solvent, an electrolyte salt, an organic additive and a sodium salt additive, the organic solvent includes a cyclic carbonate and a chain carbonate, the mass fraction of the cyclic carbonate in the electrolyte is a, the unit is %, the mass fraction of the chain carbonate in the electrolyte is b, the unit is %; the mass fraction of the organic additive in the electrolyte is c, the unit is %, and the mass fraction of the sodium salt additive in the electrolyte is d, the unit is %; The sodium ion battery satisfies the relationship: 0.4≤a / y≤0.8; 0.5≤a / b≤1.3; 0.4≤c / x≤1.2; as well as 0.1≤d / c≤0.

5.

2. The sodium ion battery according to claim 1, characterized in that The number percentage of the mesopores in the carbon material ranges from 50% to 70%.

3. The sodium ion battery according to claim 1, characterized in that The carbon material further includes macropores and micropores. The percentage of the macropores in the carbon material is in a range of 30% to 40%, and the percentage of the micropores in the carbon material is in a range of 1% to 5%.

4. The sodium ion battery according to claim 1, characterized in that The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate; the mass fraction of the cyclic carbonate in the electrolyte ranges from 29% to 45%.

5. The sodium ion battery according to claim 1, characterized in that The chain carbonate comprises at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the mass fraction of the chain carbonate in the electrolyte is in a range of 35% to 51%.

6. The sodium ion battery according to any one of claims 1 to 5, characterized in that The carbon material includes hard carbon, and the specific surface area of ​​the carbon material ranges from 3 m2 / g to 7 m2 / g.

7. The sodium ion battery according to any one of claims 1 to 5, characterized in that The organic additive includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, and tris(trimethylsilyl)phosphate; the mass fraction of the organic additive in the electrolyte ranges from 2% to 5%.

8. The sodium ion battery according to any one of claims 1 to 5, characterized in that The sodium salt additive includes at least one of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium difluorooxalatoborate, sodium bis(oxalato)borate, sodium tetrafluoroborate, sodium difluorophosphate and sodium difluorobis(oxalatophosphate); the mass fraction of the sodium salt additive in the electrolyte ranges from 0.5% to 1.5%.

9. An energy storage device, characterized in that: include: Box; as well as The sodium ion battery according to any one of claims 1 to 8, wherein the sodium ion battery is housed in the casing.

10. An energy storage system, characterized in that: include: The energy storage device according to claim 9; as well as An electric energy conversion device, the electric energy conversion device is electrically connected to the energy storage device, the electric energy conversion device is used to convert other forms of energy into electric energy, and the energy storage device is used to store the electric energy.

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