A sodium ion battery

Abstract

To overcome the problems of high impedance and Fe ion dissolution in existing sodium ion batteries, the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material contains Fe, and the surface of the positive electrode active material is coated with a coating layer. The non-aqueous electrolyte comprises a sodium salt, a non-aqueous organic solvent, and an additive. The additive comprises an additive A and an additive B. The additive A is selected from the compound shown in structural formula 1, and the additive B is selected from one or more of TMSB, NaODFB, NaBOB, NaBF4, sodium tetrakis(trifluoromethyl)borate, and sodium (trifluoromethyl)trifluoroborate. The sodium ion battery satisfies the following conditions: 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, and 0.5≤d≤2. The sodium ion battery provided by the present invention has excellent rate performance, low-temperature performance, and high-temperature performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a sodium ion battery. Background Art

[0002] Sodium-ion batteries have a similar principle and structure to lithium-ion batteries. Compared with lithium batteries, sodium-ion batteries have abundant resources, low costs and small fluctuations, and their wide temperature range and high safety performance give them alternative potential. With the continuous advancement of sodium-ion battery technology, sodium-ion batteries will occupy an important position in my country's energy system, especially in the field of energy storage, where they have broad growth space. Therefore, the development of high-performance, low-cost sodium-ion batteries is the decisive factor in determining whether they can be industrialized.

[0003] Compared with lithium-ion batteries, sodium-ion batteries still have certain disadvantages in battery performance. For example, since the radius of sodium ions is larger than that of lithium ions, it is more difficult for them to be deintercalated and intercalated in the positive and negative electrodes, resulting in low ion conduction efficiency and large battery impedance, which is more obvious under low temperature conditions and high-rate charge and discharge conditions. On the other hand, positive electrode active materials containing transition metal Fe in sodium ions have high crystal structure stability, such as Fe-containing layered oxide materials, Fe-containing Prussian blue compounds, sodium iron pyrophosphate, sodium iron sulfate, etc. However, under high temperature conditions, Fe elements will also degrade the high-temperature cycle performance of sodium-ion batteries. The reason is that under high temperature conditions, the lattice structure of the positive electrode active material is unstable, resulting in the dissolution of Fe ions in the positive electrode active material. The dissolved Fe ions cause irreversible capacity loss of the positive electrode and also cause irreversible damage to the negative electrode interface film, which in turn triggers electrolyte side reactions, generates gas, causes battery bulging, and leads to a decrease in battery capacity. Summary of the Invention

[0004] In view of the problems of high impedance and Fe ion dissolution in existing sodium ion batteries, the present invention provides a sodium ion battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] An embodiment of the present invention provides a sodium ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material contains an Fe element, the surface of the positive electrode active material is coated with a coating layer, the coating layer comprises one or more of a phosphate, a carbon material, and a metal, the non-aqueous electrolyte comprises a sodium salt, a non-aqueous organic solvent, and an additive, the additive comprising an additive A and an additive B, the additive A being selected from the compound shown in Structural Formula 1, and the additive B being selected from one or more of TMSB, NaODFB, NaBOB, NaBF4, sodium tetrakis(trifluoromethyl)borate, and sodium (trifluoromethyl)trifluoroborate;

[0007]

[0008] Wherein, n is 0 or 1, and X is selected from R1 and R2 are each independently selected from H, halogen, unsubstituted or halogen-substituted C1-C5 hydrocarbon group, R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0009] The sodium ion battery meets the following conditions:

[0010] 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.5≤d≤2;

[0011] Wherein, a is the mass percentage of additive A in the non-aqueous electrolyte, in %;

[0012] b is the mass percentage of additive B in the non-aqueous electrolyte, in %;

[0013] c is the mass percentage of Fe element in the positive electrode active material, in %;

[0014] d is the thickness of the coating layer in nm.

[0015] Optionally, the sodium ion battery meets the following conditions:

[0016] 0.2≤c / [10(a+b+d)]≤1.5.

[0017] Optionally, the mass percentage a of the additive A in the non-aqueous electrolyte is 0.3% to 1%.

[0018] Optionally, the mass percentage b of the additive B in the non-aqueous electrolyte is 1% to 3%.

[0019] Optionally, the mass percentage c of the Fe element in the positive electrode active material is 10% to 35%.

[0020] Optionally, the phosphate includes one or more of orthophosphate and pyrophosphate; and / or the carbon material includes one or more of graphite and activated carbon; and / or

[0021] The metal comprises one or more of nickel, iron, zinc, cobalt and sodium; and / or

[0022] The thickness d of the coating layer is 0.8-1.6 nm.

[0023] Optionally, the compound represented by structural formula 1 is selected from at least one of the following compounds:

[0024]

[0025]

[0026]

[0027] Optionally, the additive further comprises at least one of a cyclic carbonate compound, a fluorinated cyclic carbonate compound, a cyclic sulfonate compound, a cyclic sulfate compound, a borate compound and a nitrile compound;

[0028] Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the additive is 0.01% to 10%;

[0029] The cyclic carbonate includes at least one of vinylene carbonate, vinyl ethylene carbonate and methylene ethylene carbonate;

[0030] The fluorinated cyclic carbonate compound includes at least one of fluoroethylene carbonate and difluoroethylene carbonate;

[0031] The cyclic sulfonate ester includes at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone;

[0032] The cyclic sulfate comprises at least one of vinyl sulfate, 4-methylvinyl sulfate and propylene sulfate;

[0033] The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0034] The nitrile compound is selected from at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0035] Optionally, the positive electrode active material includes one or more of a sodium-containing layered oxide, a sodium-containing polyanion compound, and a sodium-containing Prussian blue compound.

[0036] Optionally, the sodium-containing layered oxide includes a compound represented by Formula I:

[0037] Na x Fe y M m O z Formula I

[0038] Wherein, 0<x≤1, 0<y≤1, 0<m≤1, 1<z≤2, M comprises at least one of Cr, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; and / or

[0039] The sodium-containing polyanion compound includes at least one of sodium ferric pyrophosphate and sodium ferric sulfate; and / or

[0040] The sodium-containing Prussian blue compound includes a compound shown in Formula II:

[0041] Na x′ Mn y′ [Fe(CN)6] y′ ·z′H2O formula Ⅱ

[0042] Among them, 0<x′≤2, 0<y′≤1, 0<z′≤20.

[0043] According to the sodium ion battery provided by the present invention, a positive electrode active material containing an Fe element having a coating layer is used, and additives A and additives B are added to the non-aqueous electrolyte. In order to solve the problems of high impedance and Fe ion dissolution of the sodium ion battery, the inventors have found that by controlling the content of additives A and additive B in the non-aqueous electrolyte, the content of Fe element in the positive electrode active material, and the thickness of the coating layer, so as to satisfy 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.5≤d≤2, the battery impedance can be effectively reduced, the rate performance and low temperature performance of the sodium ion battery can be improved, and the high temperature performance of the sodium ion battery can also be greatly improved. It is speculated that this is because the additives A and additives B in the battery The formation stage jointly participates in the formation of the interface film on the surface of the positive and negative electrodes. The formed interface film can effectively maintain the crystal structure stability of the positive electrode active material, inhibit the dissolution of the Fe element, and at the same time improve the high-temperature stability of the interface film on the surface of the negative electrode, thereby improving the high-temperature performance of the sodium ion battery. The content of the Fe element in the positive electrode active material and the thickness of the coating layer will affect the film formation integrity and ion conductivity of the interface film on the surface of the positive electrode. When the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material and the thickness d of the coating layer are in a synergistic state, the obtained positive electrode interface film can effectively inhibit the dissolution of the Fe element. At the same time, the positive and negative electrode interface films have a high sodium ion conduction efficiency, which plays a role in reducing the battery impedance. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0045] An embodiment of the present invention provides a sodium ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material contains an Fe element, the surface of the positive electrode active material is coated with a coating layer, the coating layer comprises one or more of a phosphate, a carbon material, and a metal. The non-aqueous electrolyte comprises a sodium salt, a non-aqueous organic solvent, and an additive, the additive comprising an additive A and an additive B, the additive A being selected from the compound shown in Structural Formula 1, and the additive B being selected from one or more of TMSB (tris(trimethylsilyl)borate), NaODFB (sodium difluorooxalatoborate), NaBOB (sodium dioxalatoborate), NaBF4, sodium tetrakis(trifluoromethyl)borate, and sodium (trifluoromethyl)trifluoroborate.

[0046]

[0047] Wherein, n is 0 or 1, and X is selected from R1 and R2 are each independently selected from H, halogen, unsubstituted or halogen-substituted C1-C5 hydrocarbon group, R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0048] The sodium ion battery meets the following conditions:

[0049] 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.5≤d≤2;

[0050] Wherein, a is the mass percentage of additive A in the non-aqueous electrolyte, in %;

[0051] b is the mass percentage of additive B in the non-aqueous electrolyte, in %;

[0052] c is the mass percentage of Fe element in the positive electrode active material, in %;

[0053] d is the thickness of the coating layer in nm.

[0054] In response to the problems of high impedance and Fe ion dissolution in sodium ion batteries, the inventors have found that by controlling the content of additives A and additive B in the non-aqueous electrolyte, the content of Fe element in the positive electrode active material, and the thickness of the coating layer, so as to satisfy 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.5≤d≤2, the battery impedance can be effectively reduced, the rate performance and low temperature performance of the sodium ion battery can be improved, and the high temperature performance of the sodium ion battery can also be greatly improved. It is speculated that this is because additives A and additive B jointly participate in the formation of the interface film on the surface of the positive and negative electrodes during the battery formation stage, and the formed interface film can have The invention effectively maintains the crystal structure stability of the positive electrode active material, inhibits the dissolution of the Fe element, and improves the high-temperature stability of the interface film on the surface of the negative electrode, thereby improving the high-temperature performance of the sodium ion battery. The content of the Fe element in the positive electrode active material and the thickness of the coating layer will affect the film formation integrity and ion conductivity of the interface film on the surface of the positive electrode. When the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material and the thickness d of the coating layer are in a synergistic state, the obtained positive electrode interface film can effectively inhibit the dissolution of the Fe element. At the same time, the positive and negative electrode interface films have a high sodium ion conduction efficiency, which plays a role in reducing the battery impedance.

[0055] In a preferred embodiment, the sodium ion battery meets the following conditions:

[0056] 0.2≤c / [10(a+b+d)]≤1.5.

[0057] When the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material and the thickness d of the coating layer further meet the above conditions, it is beneficial to further improve the rate performance, low temperature performance and high temperature performance of the sodium ion battery.

[0058] In a specific embodiment, the mass percentage a of the additive A in the non-aqueous electrolyte can be 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.8% or 2%.

[0059] In a preferred embodiment, the mass percentage a of the additive A in the non-aqueous electrolyte is 0.3% to 1%.

[0060] During the initial activation of the battery, the film-forming potential of Additive A is prioritized over that of other components in the non-aqueous electrolyte, thereby effectively reducing non-aqueous electrolyte consumption and irreversible capacity loss. Additive A, in combination with Additive B, forms a stable electrode interface film, thereby establishing a stable bipolar interface. If the amount of Additive A added is too high, the film-forming resistance at the positive and negative electrodes is too high, degrading cycle performance. If the amount of Additive A added is too low, it fails to effectively participate in film formation, resulting in insignificant improvement in battery performance.

[0061] In a specific embodiment, the mass percentage b of the additive B in the non-aqueous electrolyte can be 0.5%, 0.7%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3%, 3.2%, 3.3%, 3.5%, 3.7%, 3.8% or 4%.

[0062] In a preferred embodiment, the mass percentage b of the additive B in the non-aqueous electrolyte is 1% to 3%.

[0063] The additive B is a boron-containing additive that is used to cooperate with the additive A to form the interface film on the surface of the positive and negative electrodes. It can effectively regulate the film formation of the positive and negative electrodes, increase the composition and proportion of boron-containing inorganic salts in the interface film on the surface of the positive and negative electrodes, improve the stability of the interface film of the positive and negative electrodes and reduce the impedance. It can significantly reduce the gas production of the battery system and improve the battery rate and low-temperature performance. If the amount of additive B added is too high, the thickness of the interface film on the surface of the positive and negative electrodes will increase, the film formation impedance will be too high, and the battery performance will deteriorate rapidly. If the amount of additive B added is too low, the positive and negative electrode film formation cannot be effectively regulated, which will affect the inhibition of gas production and the improvement of rate performance.

[0064] In a specific embodiment, the mass percentage c of the Fe element in the positive electrode active material can be 8%, 10%, 13%, 15%, 17%, 18%, 20%, 23%, 25%, 27%, 28%, 30%, 33%, 35%, 37% or 40%.

[0065] In a preferred embodiment, the mass percentage c of Fe element in the positive electrode active material is 10% to 35%.

[0066] When the Fe content c in the positive electrode active material is within the above range, the positive electrode active material has good structural stability. Furthermore, the positive electrode interface film formed by the combination of additives A and B can effectively inhibit the dissolution of transition metal Fe, reduce damage to the negative electrode SEI film due to transition metal ion deposition, effectively improve the battery's cycle performance, and inhibit battery gas production. If the Fe content in the positive electrode active material is too low, the battery energy density is too low, the material's intrinsic stability is poor, and the cycle life is shortened. If the Fe content in the positive electrode active material is too high, this is also detrimental to improving the material's intrinsic stability, resulting in significant Fe ion dissolution and a shortened battery life.

[0067] In some embodiments, the phosphate includes one or more of orthophosphate and pyrophosphate.

[0068] In some embodiments, the carbon material includes one or more of graphite and activated carbon.

[0069] In some embodiments, the metal includes one or more of nickel, iron, zinc, cobalt, and sodium.

[0070] In a specific embodiment, the thickness d of the coating layer can be 0.5 nm, 0.7 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.8 nm or 2 nm.

[0071] In a preferred embodiment, the thickness d of the coating layer is 0.8-1.6 nm.

[0072] The coating layer is used to improve the stability of the positive electrode active material while also providing good ion transport performance. Furthermore, the coating layer serves as a substrate for the interface film on the surface of the positive electrode active material, thereby influencing the film-forming effect of the additives A and B. When the thickness d of the coating layer is within the aforementioned range, it effectively protects the positive electrode, inhibiting the dissolution of transition metal ions from the positive electrode, particularly effectively limiting the dissolution of Fe ions, thereby effectively improving the battery's cycle performance and suppressing gas production.

[0073] In some embodiments, the compound represented by Structural Formula 1 is selected from at least one of the following compounds:

[0074]

[0075]

[0076]

[0077] In some embodiments, the additive further comprises at least one of a cyclic carbonate compound, a fluorinated cyclic carbonate compound, a cyclic sulfonate compound, a cyclic sulfate compound, a borate compound, and a nitrile compound.

[0078] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the additive is 0.01% to 10%.

[0079] In some embodiments, the cyclic carbonate includes at least one of vinylene carbonate, vinyl ethylene carbonate, and methylene ethylene carbonate.

[0080] In some embodiments, the fluorinated cyclic carbonate compound includes at least one of fluoroethylene carbonate and bisfluoroethylene carbonate.

[0081] In some embodiments, the cyclic sulfonate includes at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.

[0082] In some embodiments, the cyclic sulfate comprises at least one of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate.

[0083] In some embodiments, the borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0084] In some embodiments, the nitrile compound is selected from at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile.

[0085] In some embodiments, the non-aqueous organic solvent includes at least one of an ether solvent, a nitrile solvent, a carbonate solvent, a carboxylate solvent, and a sulfone solvent.

[0086] In some embodiments, the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether with 3 to 10 carbon atoms and a cyclic ether with 3 to 6 carbon atoms. The cyclic ether may be, but is not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether may be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with sodium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have low viscosity and can impart high ionic conductivity. The ether compound can be used alone or in any combination and ratio. There is no special restriction on the amount of ether compound added, and it is arbitrary within the range that does not significantly damage the effect of the sodium ion battery of the present invention. The volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more in the non-aqueous solvent volume ratio of 100%. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of the ether compounds can be made to meet the above range. When the amount of ether compound added is within the above preferred range, it is easy to ensure the improvement effect of ionic conductivity brought about by the increase in the ionic dissociation degree of the chain ether and the reduction in viscosity.

[0087] In some embodiments, the nitrile solvent may be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.

[0088] In some embodiments, the carbonate solvent includes a cyclic carbonate or a chain carbonate. The cyclic carbonate may be, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate may be, but is not limited to, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the sodium ion battery of the present invention. However, when one is used alone, the lower limit of its content is generally 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the decrease in conductivity due to the decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, and it is easy to achieve a good range for the high current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. In addition, the upper limit is generally 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolyte can be improved, thereby contributing to the stability during high temperature storage. The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolyte, is usually more than 15% by volume, preferably more than 20% by volume, and more preferably more than 25% by volume. In addition, usually the volume ratio is less than 90%, preferably less than 85% by volume, and more preferably less than 80% by volume. By making the content of linear carbonate in the above-mentioned scope, it is easy to make the viscosity of nonaqueous electrolyte reach appropriate range, suppress the reduction of ionic conductivity, and then contribute to the output characteristics of nonaqueous electrolyte battery reach good scope. When using two or more linear carbonates in combination, make the total amount of linear carbonate meet the above-mentioned scope.

[0089] In certain embodiments, also can preferably use the linear carbonates with fluorine atoms (hereinafter referred to as " fluorinated linear carbonate ").The number of the fluorine atoms possessed by fluorinated linear carbonate is as long as being more than 1 then has no particular restrictions, but is generally below 6, preferably below 4.When fluorinated linear carbonate has a plurality of fluorine atoms, these fluorine atoms can be bonded on the same carbon, also can be bonded on different carbons.As fluorinated linear carbonate, can enumerate, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives etc.

[0090] Carboxylate solvents include cyclic carboxylates and / or chain carbonates. Examples of cyclic carboxylates include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0091] In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone. Preferably, in the case of a cyclic sulfone, it is generally a compound having 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of a chain sulfone, it is generally a compound having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no particular limitation on the amount of sulfone solvent added, and it is arbitrary within the range that does not significantly damage the effect of the sodium ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, the volume ratio is generally 0.3% or more, preferably 0.5% or more, more preferably 1% or more. In addition, the volume ratio is generally 40% or less, preferably 35% or less, more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvent can be made to meet the above range. When the amount of sulfone solvent added is within the above range, an electrolyte with excellent high-temperature storage stability tends to be obtained.

[0092] In some embodiments, the sodium salt includes at least one of sodium perchlorate, sodium hexafluorophosphate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0093] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the sodium salt is 6% to 18%.

[0094] In some embodiments, the positive electrode active material includes one or more of a sodium-containing layered oxide, a sodium-containing polyanion compound, and a sodium-containing Prussian blue compound.

[0095] In a preferred embodiment, the sodium-containing layered oxide comprises a compound represented by Formula I:

[0096] Na x Fe y M m O z Formula I

[0097] Wherein, 0<x≤1, 0<y≤1, 0<m≤1, 1<z≤2, M comprises at least one of Cr, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; and / or

[0098] The sodium-containing polyanion compound includes at least one of sodium ferric pyrophosphate (NaFePO4) and sodium ferric sulfate (Na2Fe(SO4)2); and / or

[0099] The sodium-containing Prussian blue compound includes a compound shown in Formula II:

[0100] Na x′ Mn y′[Fe(CN)6] y′ ·z′H2O formula Ⅱ

[0101] Among them, 0<x′≤2, 0<y′≤1, 0<z′≤20.

[0102] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on a surface of the positive electrode current collector.

[0103] The positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel.

[0104] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0105] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0106] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0107] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes one or more of hard carbon and soft carbon.

[0108] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, which will not be described in detail here.

[0109] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended together to form the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent may be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and are not further described here.

[0110] In some embodiments, the sodium ion battery further includes a separator, which is located between the positive electrode and the negative electrode.

[0111] The diaphragm can be an existing conventional diaphragm, which can be a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, an inorganic-organic composite diaphragm, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and three-layer PP / PE / PP diaphragms.

[0112] The present invention is further described below with reference to the following examples.

[0113] Table 1

[0114]

[0115]

[0116]

[0117] Example 1

[0118] This embodiment is used to illustrate the sodium ion battery and its preparation method disclosed in the present invention, which includes the following steps:

[0119] 1) Preparation of non-aqueous electrolyte:

[0120] Ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a mass ratio of 2:1:7, and then sodium hexafluorophosphate (NaPF6) was added to a mass concentration of 12%. Additives were added. The total weight of the non-aqueous electrolyte was 100%. The types and contents of the additives are shown in Table 1.

[0121] 2) Preparation of positive electrode sheet:

[0122] The positive electrode active material NaNi was mixed in a mass ratio of 93:4:3 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, conductive carbon black Super-P, and a binder of polyvinylidene fluoride (PVDF) are then dispersed in N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The Fe content of the positive electrode active material is shown in Table 1. The surface of the positive electrode active material is coated with a coating layer of sodium manganate, the coating layer thickness of which is shown in Table 1. The slurry is evenly coated on both sides of aluminum foil, dried, rolled, and vacuum-dried, and then ultrasonically welded with aluminum or nickel lead wires to produce a positive electrode sheet with a thickness between 120 and 150 μm.

[0123] 3) Preparation of negative electrode sheet:

[0124] The negative electrode active material, spherical hard carbon, conductive carbon black Super-P, and binders styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC), are mixed in a mass ratio of 97:1:1:1 and dispersed in deionized water to create a negative electrode slurry. The slurry is then coated on both sides of aluminum foil, dried, rolled, and vacuum-dried. Aluminum or nickel lead wires are then ultrasonically welded to create a negative electrode sheet with a thickness ranging from 80 to 300 μm.

[0125] 4) The positive electrode sheet, separator, and negative electrode sheet are stacked in order, and the preparation of the sodium ion battery is completed by aluminum-plastic film packaging, re-baking, liquid injection, static standing, formation, fixture shaping, secondary sealing, and capacity testing.

[0126] Examples 2 to 22

[0127] Examples 2 to 22 are used to illustrate the sodium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0128] The positive electrode active materials, additives and their addition amounts shown in Examples 2 to 22 in Table 1 were used.

[0129] Comparative Examples 1 to 14

[0130] Comparative Examples 1 to 14 are used to illustrate the sodium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0131] The positive electrode active materials, additives and their addition amounts shown in Comparative Examples 1 to 14 in Table 1 were used.

[0132] Performance Testing

[0133] The sodium ion batteries prepared in the examples and comparative examples were subjected to the following performance tests:

[0134] 1. -20℃ discharge performance

[0135] The formed sodium ion battery is charged at room temperature with a constant current of 0.2C to the cut-off voltage, then charged at a constant voltage until the current drops to 0.03C, and then discharged at a constant current of 0.2C to 1.5V, and the discharge capacity D1 is recorded; at room temperature, the sodium ion battery is charged at a constant current of 0.2C to the cut-off voltage, then charged at a constant voltage until the current drops to 0.03C, and then the sodium ion battery is placed at 20°C and discharged at a constant current of 0.2C to 1.5V, and the discharge capacity D2 is recorded; the calculation method is as follows:

[0136] -20°C capacity retention rate (%) = D2 / D1×100%.

[0137] 2. 6C rate discharge capacity ratio test

[0138] The formed sodium ion battery is charged at room temperature at a constant current of 0.2C to the cut-off voltage, then charged at a constant voltage until the current drops to 0.03C, and then discharged at a constant current of 0.2C to 1.5V, and the discharge capacity D3 is recorded; at room temperature, the sodium ion battery is charged at a constant current of 0.2C to the cut-off voltage, then charged at a constant voltage until the current drops to 0.03C, and then discharged at a constant current of 6C to 1.5V, and the discharge capacity D4 is recorded; the calculation method is as follows:

[0139] 6C rate discharge capacity ratio (%) = D4 / D3×100%.

[0140] 3. High temperature cycle performance test

[0141] The formed sodium ion battery was charged at 45°C at a constant current of 0.5C to the cut-off voltage, then charged at a constant current and constant voltage until the current dropped to 0.03C, and then discharged at a constant current of 1C to 1.5V. This cycle was repeated for 600 cycles. The battery's discharge capacity in the first week, initial discharge capacity in the 600th week, volume in the first week, and volume in the 600th week were measured, and the calculation formula is as follows:

[0142] Capacity retention rate (%) = discharge capacity at the 600th week / discharge capacity at the first week × 100%;

[0143] Gas production (mL) = volume at the 600th week - volume at the first week.

[0144] 4. Fe ion dissolution test after 400 cycles at 45℃

[0145] The battery after 400 cycles was disassembled, the negative electrode was digested, and the sample was sent for ICP detection of Fe ion content.

[0146] (1) The test results obtained in Examples 1 to 14 and Comparative Examples 1 to 14 are shown in Table 2.

[0147] Table 2

[0148]

[0149]

[0150] It can be seen from the test results of Examples 1 to 14 and Comparative Examples 1 to 14 that in a battery system using an Fe-containing positive electrode active material with a coating layer, additives A and additive B are added to the non-aqueous electrolyte as additives, and by controlling the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material, and the thickness d of the coating layer to satisfy the relationship: 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.5≤d≤2, the obtained sodium ion battery can have a low flatulence rate, a high capacity retention rate, and low Fe ion dissolution under high temperature cycling and high temperature storage conditions. At the same time, the sodium ion battery has a low impedance and adapts to the cycling requirements of high rate charge and discharge and low temperature environment. It is speculated that additives A and B jointly participate in the formation of the interface film on the surface of the positive and negative electrodes during the battery formation stage. The formed interface film can effectively maintain the crystal structure stability of the positive electrode active material, inhibit the dissolution of the Fe element, and at the same time improve the high-temperature stability of the interface film on the surface of the negative electrode, thereby improving the high-temperature performance of the sodium ion battery. The content of the Fe element in the positive electrode active material and the thickness of the coating layer will affect the film formation integrity and ion conductivity of the interface film on the surface of the positive electrode. When the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material and the thickness d of the coating layer are in a synergistic state, the interface film on the surface of the obtained positive electrode material layer has the effect of uniform and dense coverage and strong high-temperature stability for the positive electrode active material, can inhibit the dissolution of the Fe element, and at the same time, the interface film has a high sodium ion conduction efficiency, which plays a role in reducing the battery impedance.

[0151] From the test results of Examples 1-14, it can be seen that when the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material and the thickness d of the coating layer further satisfy the conditions 0.2≤c / [10(a+b+d)]≤1.5, and 0.3≤a≤1, 1≤b≤3, 10≤c≤35, 0.8≤d≤1.6, the obtained sodium ion battery has the best electrochemical performance under high temperature conditions, low temperature conditions and high rate charge and discharge conditions.

[0152] From the test results of Comparative Examples 1 to 8, it can be seen that when one or more of the a value, b value, c value, and d value exceed the specified range, even if the relationship: 0.2≤c / [10(a+b+d)]≤2.3 is satisfied, the electrochemical performance of the obtained sodium ion battery at high and low temperatures is poor, and the 6C discharge capacity is significantly reduced. This indicates that when the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material, and the thickness d of the coating layer are too high or too low, the film density, stability, and ion permeability of the interface film on the surface of the positive and negative electrode material layers will be affected, resulting in uneven film formation and increased impedance, which in turn causes the non-aqueous electrolyte to decompose and produce gas on the positive electrode surface. From the test results of Comparative Examples 9 to 14, it can be seen that even if the a value, b value, c value and d value all meet the parameter range limits, if the c / [10(a+b+d)] value is too large or too small, it will lead to the degradation of the high and low temperature performance and high rate charge and discharge performance of the sodium ion battery, indicating that there is a mutual influence between the mass percentage a of the additive A, the mass percentage b of the additive B, the mass percentage c of the Fe element in the positive electrode active material and the thickness d of the coating layer. When and only when the four reach a better balance, the high and low temperature performance and high rate charge and discharge performance of the sodium ion battery can be significantly improved.

[0153] (2) The test results obtained in Examples 1 and 15 to 17 are entered in Table 2.

[0154] Table 2

[0155]

[0156] From the test results obtained in Examples 1 and 15 to 17, it can be seen that on the basis of the battery system provided by the present invention, the high and low temperature performance and high rate discharge performance of the obtained sodium ion battery are not significantly improved by additionally adding FEC (fluoroethylene carbonate), DTD (vinyl sulfate) or PS (1,3-propane sultone). This shows that the interface film formed by the battery system provided by the present invention is capable of achieving complete coverage of the surface of the positive electrode active material and the surface of the negative electrode active material, while the film-forming improvement effect of the traditional film-forming additives FEC (fluoroethylene carbonate), DTD (vinyl sulfate) or PS (1,3-propane sultone) is not obvious.

[0157] (3) The test results obtained in Examples 1 and 18 to 22 are entered in Table 3.

[0158] Table 3

[0159]

[0160] From the test results obtained in Examples 1 and 18 to 22, it can be seen that in the battery system provided by the present invention, when different additives A and additives B are used, the mass percentage a of additive A, the mass percentage b of additive B, the mass percentage c of Fe element in the positive electrode active material and the thickness d of the coating layer satisfy the conditions: 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.5≤d≤2. The obtained sodium ion battery also has lower impedance and better high and low temperature performance, indicating that the battery system provided by the present invention is suitable for different additives A and additives B.

[0161] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A sodium ion battery, characterized in that The invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material contains Fe element, the surface of the positive electrode active material is coated with a coating layer, the coating layer comprises one or more of phosphate, carbon material and metal, the non-aqueous electrolyte comprises a sodium salt, a non-aqueous organic solvent and an additive, the additive comprises an additive A and an additive B, the additive A is selected from the compound shown in structural formula 1, and the additive B is selected from one or more of TMSB, NaODFB, NaBOB, NaBF4, sodium tetrakis(trifluoromethyl)borate and sodium (trifluoromethyl)trifluoroborate; Structural formula 1 Wherein, n is 0 or 1, and X is selected from or , R1, R2 are each independently selected from 、 or , and X, R1 and R2 contain at least one sulfur atom; The sodium ion battery meets the following conditions: 0.2≤c / [10(a+b+d)]≤2.3, and 0.2≤a≤2, 0.5≤b≤4, 8≤c≤40, 0.8≤d≤1.6; Wherein, a is the mass percentage of additive A in the non-aqueous electrolyte, unit is %; b is the mass percentage of additive B in the non-aqueous electrolyte, unit is %; c is the mass percentage of Fe element in the positive electrode active material, unit is %; d is the thickness of the coating layer in nm.

2. The sodium ion battery according to claim 1, characterized in that The sodium ion battery meets the following conditions: 0.2≤c / [10(a+b+d)]≤1.

5.

3. The sodium ion battery according to claim 1, characterized in that The mass percentage a of the additive A in the non-aqueous electrolyte is 0.3% to 1%.

4. The sodium ion battery according to claim 1, characterized in that The mass percentage b of the additive B in the non-aqueous electrolyte is 1% to 3%.

5. The sodium ion battery according to claim 1, characterized in that The mass percentage c of the Fe element in the positive electrode active material is 10% to 35%.

6. The sodium ion battery according to claim 1, characterized in that The phosphate includes one or more of orthophosphate and pyrophosphate; and / or The carbon material includes one or more of graphite and activated carbon; and / or The metal includes one or more of nickel, iron, zinc, cobalt and sodium.

7. The sodium ion battery according to claim 1, characterized in that The compound represented by structural formula 1 is selected from at least one of the following compounds: 。 8. The sodium ion battery according to claim 1, characterized in that The additive further comprises at least one of a cyclic carbonate compound, a fluorinated cyclic carbonate compound, a cyclic sulfonate compound, a cyclic sulfate compound, a borate compound and a nitrile compound; Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the additive is 0.01% to 10%; The cyclic carbonate includes at least one of vinylene carbonate, vinyl ethylene carbonate and methylene ethylene carbonate; The fluorinated cyclic carbonate compound includes at least one of fluoroethylene carbonate and difluoroethylene carbonate; The cyclic sulfonate ester includes at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone; The cyclic sulfate comprises at least one of vinyl sulfate, 4-methylvinyl sulfate and propylene sulfate; The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate; The nitrile compound is selected from at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

9. The sodium ion battery according to claim 1, characterized in that The positive electrode active material includes one or more of a sodium-containing layered oxide, a sodium-containing polyanion compound, and a sodium-containing Prussian blue compound.

10. The sodium ion battery according to claim 9, characterized in that The sodium-containing layered oxide includes a compound shown in Formula I: Na x Fe y M m O z Formula I Wherein, 0<x≤1, 0<y≤1, 0<m≤1, 1<z≤2, M comprises at least one of Cr, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; and / or The sodium-containing polyanion compound includes at least one of sodium ferric pyrophosphate and sodium ferric sulfate; and / or The sodium-containing Prussian blue compound includes a compound shown in Formula II: Na x´ Mn y´ [Fe(CN)6] y´ •z´H2O formula II Among them, 0<x´≤2, 0<y´≤1, 0<z´≤20.

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