Sodium-ion battery

Abstract

Provided is a sodium-ion battery, comprising a non-aqueous electrolyte, a positive electrode and a negative electrode, wherein the non-aqueous electrolyte comprises an additive, and the additive comprises a sodium-salt-type additive; the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprises a sodium-replenishing additive and a positive electrode active material, and the sodium-replenishing additive is a sodium-rich transition metal oxide; and the negative electrode comprises a negative electrode active material. The sodium-ion battery satisfies the following relational expression: 0.3≤a / (b+c)≤1.5, wherein 5≤a≤10, 1≤b≤10, and 2≤c≤12; the total mass of the sodium-replenishing additive and the positive electrode active material is 100%; a is the mass content of the sodium-replenishing additive, the unit thereof being %; b is the mass content of the sodium-salt-type additive in the non-aqueous electrolyte, the unit thereof being %; and c is the particle size of the negative electrode active material, the unit thereof being μm. The internal resistance of the sodium-ion battery provided can be reduced, and the initial efficiency and cycle performance thereof can be improved.

Description

A sodium ion battery 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 (SIBs) share similar principles and structures to lithium-ion batteries. Compared to lithium batteries, SIBs offer abundant resources, low cost, minimal fluctuations, and a wide temperature range and high safety profile, making them a promising alternative. With the continuous advancement of SIB technology, SIBs are poised to occupy a significant position in my country's energy system, particularly in the energy storage sector, where they hold broad growth potential. Therefore, the development of high-performance, low-cost SIBs is crucial for their industrialization. Hard carbon, due to its stable structure, high conductivity, high sodium storage capacity, and high capacity, has become one of the most promising anode materials for SIBs, with the greatest potential for industrial application. However, due to its numerous defects and large surface area, SIBs experience significant irreversible sodium ion loss, resulting from the formation of SEI films and side reactions at the electrode interface. This directly impacts the energy density and cycle life of SIBs, particularly for full SIBs. To address these issues, researchers are using various sodium supplementation techniques to compensate for this irreversible sodium ion loss and improve the initial efficiency of SIBs. For example, the existing Chinese patent CN111293290A discloses a sodium-rich transition metal oxide composite sodium-supplementing positive electrode active material, wherein the sodium-supplementing additive is a sodium-rich transition metal oxide with a chemical formula of Na x MO y ; Wherein, M is one or more of Ni, Co, Fe, Mn, Ru, Ir, Sn, Cr, Cu, Nb, and Mo. This material uses a mixture of two or more sodium-supplementing materials as a positive electrode additive, which can effectively compensate for the active sodium loss of sodium-ion batteries. However, the sodium-rich metal oxides used as sodium-supplementing additives have the characteristics of poor conductivity, high impedance, high activity, and easy decomposition and gas production. The prepared battery has low initial efficiency and poor cycle performance. Therefore, it is of great significance to develop sodium-ion batteries that can improve the sodium-supplementing additives added with sodium-rich transition metal oxides.

[0003] Summary of the Invention

[0004] To address the technical problems of low initial efficiency and low cycle performance of existing sodium ion batteries that incorporate sodium-rich transition metal oxide sodium supplement additives, the present application provides a sodium ion battery.

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

[0006] On the one hand, the present application provides a sodium ion battery, comprising a non-aqueous electrolyte, a positive electrode and a negative electrode, wherein the non-aqueous electrolyte comprises an additive, wherein the additive comprises a sodium salt additive; the positive electrode comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a sodium supplement additive and a positive electrode active material, wherein the sodium supplement additive is a sodium-rich transition metal oxide; the negative electrode comprises a negative electrode active material,

[0007] The sodium ion battery satisfies the following relationship:

[0008] 0.3≤a / (b+c)≤1.5, and 5≤a≤10, 1≤b≤10, 2≤c≤12;

[0009] Wherein, the total mass of the sodium supplement additive and the positive electrode active material is 100%, a is the mass content of the sodium supplement additive, unit %;

[0010] b is the mass content of the sodium salt additive in the non-aqueous electrolyte, in %;

[0011] c is the particle size of the negative electrode active material, in μm.

[0012] Preferably, the sodium ion battery satisfies the following relationship: 0.5≤a / (b+c)≤1.2.

[0013] Preferably, the total mass of the sodium-supplementing additive and the positive electrode active material is 100%, and the mass content a of the sodium-supplementing additive is in the range of 5.5-9%.

[0014] Preferably, the sodium salt additive includes one or more of sodium bis(fluorosulfonyl)imide, sodium difluorooxalatoborate, and sodium difluorophosphate;

[0015] The mass content b of the sodium salt additive in the non-aqueous electrolyte is in the range of 2% to 6%.

[0016] Preferably, the particle size c of the negative electrode active material is in the range of 3 μm to 9 μm.

[0017] Preferably, the additive further comprises 1,3-propane sultone, and the mass content of the 1,3-propane sultone in the non-aqueous electrolyte is 0.5% to 2%.

[0018] Preferably, the mass content of the 1,3-propane sultone in the non-aqueous electrolyte is 1% to 2%.

[0019] Preferably, the sodium-rich transition metal oxide includes a compound represented by Formula 1,

[0020] Na x M y O z Formula 1,

[0021] Among them, 0.2<x / y<9, 0<y<6, 2≤z≤9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr.

[0022] Preferably, the sodium-rich transition metal oxide includes one or more of Na5NbO5, Na3NbO4, Na4Nb2O7, Na5VO5, Na3VO4, and Na3TaO4.

[0023] Preferably, the non-aqueous electrolyte further comprises an electrolyte salt, an auxiliary additive and a non-aqueous organic solvent.

[0024] The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium trifluoromethylsulfonyl imide, sodium trifluoromethylsulfonate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate and sodium bis(trifluoromethylsulfonyl)imide;

[0025] Based on the mass of the electrolyte being 100%, the mass content of the electrolyte salt is 8% to 14%;

[0026] The auxiliary additive comprises at least one of 1,4-butane sultone, acrylic acid lactone, vinyl sulfate and fluoroethylene carbonate;

[0027] Taking the mass of the electrolyte as 100%, the mass content of the auxiliary additive is 2.5% to 10%;

[0028] The non-aqueous organic solvent includes at least one of carbonates with 3 to 5 carbon atoms, carboxylates with 2 to 6 carbon atoms, and ethers with 4 to 10 carbon atoms;

[0029] The positive electrode active material includes at least one of a layered transition metal oxide, a Prussian compound, a phosphate compound, and a sulfate compound;

[0030] The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes one or more of a carbon-based material, a silicon-based material, and a tin-based material. Beneficial effects:

[0031] In the sodium ion battery provided by the present application, the total mass of the sodium supplement additive and the positive electrode active material is 100%, a is the mass content of the sodium supplement additive, and it has a synergistic effect with the sodium salt additive and the negative electrode active material. There is a certain relationship between the mass content a of the sodium supplement additive and the mass content b of the sodium salt additive added to the electrolyte and the particle size c of the negative electrode active material. When a, b, and c satisfy the relationship 0.3≤a / (b+c)≤1.5, it can effectively improve the conductivity of the electrolyte and the diffusion and transmission rate of ions in the negative electrode material while ensuring the optimal conductivity of the positive electrode, thereby effectively reducing the overall internal resistance of the battery and improving the first efficiency and cycle performance of the battery. In addition, the addition of the sodium salt additive to the electrolyte will also participate in the formation of the positive and negative electrode interface film, effectively protecting the stability of the negative electrode during the test, thereby further improving the cycle performance. DETAILED DESCRIPTION

[0032] 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.

[0033] On one hand, the present application provides a sodium ion battery, comprising a non-aqueous electrolyte, a positive electrode, and a negative electrode, wherein the non-aqueous electrolyte comprises an additive, wherein the additive comprises a sodium salt additive; the positive electrode comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a sodium-supplementing additive and a positive electrode active material, wherein the sodium-supplementing additive is a sodium-rich transition metal oxide; and the negative electrode comprises a negative electrode active material.

[0034] The sodium ion battery satisfies the following relationship:

[0035] 0.3≤a / (b+c)≤1.5, and 5≤a≤10, 1≤b≤10, 2≤c≤12;

[0036] Wherein, the total mass of the sodium supplement additive and the positive electrode active material is 100%, a is the mass content of the sodium supplement additive, unit %;

[0037] b is the mass content of the sodium salt additive in the non-aqueous electrolyte, in %;

[0038] c is the particle size of the negative electrode active material, in μm.

[0039] Sodium-rich transition metal oxide is added to the sodium ion battery as a sodium supplement additive. The sodium supplement additive has the characteristics of poor conductivity, high impedance, high activity, and easy decomposition and gas production. The prepared battery has low first efficiency and cycle performance. To address this problem, the inventors have found through extensive research that the total mass of the sodium supplement additive and the positive electrode active material is 100%, a is the mass content of the sodium supplement additive, and it has a synergistic effect with the sodium salt additive and the negative electrode active material. There is a certain relationship between the mass content a of the sodium supplement additive and the mass content b of the sodium salt additive added to the electrolyte and the particle size c of the negative electrode active material. When a, b, and c satisfy the relationship 0.3≤a / (b+c)≤1.5, it can effectively improve the conductivity of the electrolyte and the diffusion and transmission rate of ions in the negative electrode material while ensuring the optimal conductivity of the positive electrode, thereby effectively reducing the overall internal resistance of the battery and improving the first efficiency and cycle performance of the battery. In addition, the addition of the sodium salt additive to the electrolyte will also participate in the formation of the positive and negative electrode interface film, effectively protecting the stability of the negative electrode during the test, thereby further improving the cycle performance.

[0040] In some preferred embodiments, the sodium ion battery satisfies the following relationship: 0.5≤a / (b+c)≤1.2.

[0041] Sodium-ion batteries satisfy the relationship 0.5≤a / (b+c)≤1.2. The conductivity of the positive electrode is relatively high, and the conductivity of the electrolyte is greatly improved, which increases the diffusion and transmission rate of sodium ions in the negative electrode active material, thereby effectively reducing the overall internal resistance of the battery and improving the battery's initial efficiency and cycle performance. In addition, the addition of sodium salt additives to the electrolyte will also participate in the negative electrode film formation, and can form a more stable interface film at the electrode interface, preventing the residual byproducts of the sodium supplement additive from damaging the positive and negative electrodes, effectively protecting the stability of the negative electrode during testing, and further improving the cycle performance.

[0042] Specifically, the relationship a / (b+c) value of the sodium ion battery can be 0.3, 0.5, 0.6, 0.8, 1.0, 1.2, 1.4, 1.5, etc., as long as the relationship a / (b+c) value is between 0.3 and 1.5. Specifically, the mass content b of the sodium salt type additive in the electrolyte in the non-aqueous electrolyte is in the range of 1% to 10%, which has the effect of improving the overall conductivity of the electrolyte, and can also play a role in participating in the formation of the positive and negative electrode interface film, protecting the positive and negative electrodes, and effectively solving the problem of poor conductivity of the sodium supplement additive and the damage of the residual by-products to the positive and negative electrodes, improving battery performance, and improving battery cycle performance. If the mass content b of the sodium salt type additive in the electrolyte in the non-aqueous electrolyte is less than 1%, the effect of improving the conductivity of the electrolyte is not obvious, and it cannot effectively participate in the formation of the positive and negative electrode interface film. If b is greater than 10%, the mass content of the sodium salt type additive in the electrolyte is too high, the thickness of the interface film formed at the electrode interface is thicker, the transmission rate of sodium ions is reduced, and the battery impedance increases. Specifically, the mass content b of the sodium salt additive in the electrolyte can be 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10%, etc., as long as the range of b is between 1% and 10%.

[0043] In some preferred embodiments, the mass content b of the sodium salt additive in the non-aqueous electrolyte is in the range of 2% to 6%.

[0044] The mass content of the sodium salt additive added to the electrolyte is within the above-mentioned preferred range, which can improve the overall conductivity of the electrolyte while also forming an interface film with moderate thickness and stable structure at the interface of the positive and negative electrodes, effectively solving the problem of poor conductivity of the sodium supplement additive and damage to the positive and negative electrodes by residual by-products, thereby better improving battery performance and improving battery cycle performance.

[0045] In some embodiments, the sodium salt additive includes one or more of sodium bis(fluorosulfonyl)imide (NaFSI), sodium difluorooxalatoborate (NaODFB), and sodium difluorophosphate (NaPO2F2).

[0046] In some embodiments, the total mass of the sodium-supplementing additive and the positive electrode active material is 100%, and the mass content a of the sodium-supplementing additive is in the range of 5% to 10%.

[0047] Since the sodium-supplementing additive itself has poor conductivity and there will be residual by-products after the reaction, when the mass content a of the sodium-supplementing additive is greater than 10%, the overall performance of the positive electrode material deteriorates; when the mass content a of the sodium-supplementing additive is less than 5%, it will not have the effect of sodium supplementation. In sodium-ion batteries, taking the total mass of the sodium-supplementing additive and the positive electrode active material as 100%, the mass content a of the sodium-supplementing additive ranges from 5% to 10%. The sodium-supplementing additive can better play the role of sodium supplementation while also improving the conductivity of the positive electrode, and reducing the residual by-products after the reaction of the sodium-supplementing additive, thereby improving the first efficiency and cycle performance of the battery. Specifically, a can be 5%, 5.5%, 6%, 6.4%, 7.0%, 7.3%, 7.6%, 8.0%, 9%, 10%, etc., as long as the value of a is within the range of 5% to 10%.

[0048] In some preferred embodiments, the total mass of the sodium-supplementing additive and the positive electrode active material is 100%, and the mass content a of the sodium-supplementing additive is in the range of 5.5-9%.

[0049] Within the above preferred range, the sodium-supplementing additive in the sodium-ion battery can not only play a good role in replenishing sodium, but also improve the conductivity of the positive electrode sheet and improve the initial efficiency and cycle performance of the battery.

[0050] In some embodiments, the sodium-rich transition metal oxide comprises a compound represented by Formula 1,

[0051] Na x M y O z Formula 1,

[0052] Among them, 0.2<x / y<9, 0<y<6, 2≤z≤9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr.

[0053] In some preferred embodiments, the sodium-rich transition metal oxide includes one or more of Na5NbO5, Na3NbO4, Na4Nb2O7, Na5VO5, Na3VO4, and Na3TaO4. It is understood that the present application does not limit the types of the above sodium-rich transition metal oxides.

[0054] In some embodiments, the particle size c of the negative electrode active material ranges from 2 μm to 12 μm.

[0055] The particle size of the negative electrode active material of 2 to 12 μm can ensure a faster ion transfer rate within and between the particles of the negative electrode active material, thereby further improving the disadvantage of deteriorating battery rate performance due to sodium supplementation additives and improving the cycle performance of the battery. If the particle size c of the negative electrode active material is greater than 12 μm, the internal resistance of the battery increases and the cycle performance is poor; if the particle size c of the negative electrode active material is less than 2 μm, the particle size is too small to reduce the first efficiency of the battery. Specifically, the particle size c of the negative electrode active material can be 3 μm, 4 μm, 5 μm, 5.5 μm, 6 μm, 7.5 μm, 8 μm, 9 μm, 10 μm, 12 μm, etc., as long as the range of c is between 3 μm-12 μm.

[0056] In some preferred embodiments, the particle size c of the negative electrode active material ranges from 3 μm to 9 μm.

[0057] When the particle size c of the negative electrode active material is within the above preferred range, the transmission efficiency of sodium ions can be better improved, and the cycle performance of the battery can be better improved.

[0058] In some embodiments, the additive further comprises 1,3-propane sultone, and the mass content of the 1,3-propane sultone in the non-aqueous electrolyte is 0.5% to 2%.

[0059] Specifically, 1,3-propane sultone (PS) with a mass content of 0.5% to 2% in the electrolyte can effectively inhibit the occurrence of electrode surface side reactions and the dissolution and precipitation of metal ions on the positive electrode surface, stabilize the positive electrode crystal structure, effectively reduce the internal resistance and gas production of the battery, and improve the cycle performance. Specifically, if the PS content in the electrolyte is lower than 0.5%, it cannot effectively inhibit the dissolution and precipitation of metal ions at the positive electrode interface. If the PS content in the electrolyte is higher than 2%, the thickness of the electrode interface film formed in the electrolyte increases, and the battery impedance increases. Specifically, the mass content of 1,3-propane sultone in the electrolyte can be 0.5%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9%, 2.0%, etc., as long as it is between 0.5 and 2%.

[0060] In some preferred embodiments, the mass content of the 1,3-propane sultone in the non-aqueous electrolyte is 1% to 2%.

[0061] The mass content of 1,3-propane sultone is within this preferred range, which can effectively inhibit the dissolution and precipitation of metal ions at the positive electrode interface, while also participating in the formation of a structurally stable interface film, thereby reducing the internal resistance of the battery and gas production.

[0062] In some embodiments, the non-aqueous electrolyte further comprises an electrolyte salt, wherein the electrolyte salt comprises at least one of sodium hexafluorophosphate, sodium trifluoromethylsulfonyl imide, sodium trifluoromethylsulfonate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate, and sodium bis(trifluoromethylsulfonyl)imide;

[0063] Based on the mass of the electrolyte being 100%, the mass content of the electrolyte salt is 8% to 14%.

[0064] Electrolyte salts are added to the electrolyte, which have high solubility in non-aqueous organic solvents and are easy to dissociate, to ensure that the electrolyte has high ionic conductivity and promote the redox reaction of the battery.

[0065] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, wherein the auxiliary additive includes at least one of 1,4-butane sultone, propylene glycol (RPS), dithiothreitol (DTD) and fluoroethylene carbonate, and the mass content of the auxiliary additive is 2.5% to 10% based on the mass of the electrolyte being 100%.

[0066] In some embodiments, the non-aqueous electrolyte further includes a non-aqueous organic solvent, and the non-aqueous organic solvent includes at least one of carbonates with 3 to 5 carbon atoms, carboxylates with 2 to 6 carbon atoms, and ethers with 4 to 10 carbon atoms.

[0067] Preferably, the carbonate solvent having 3 to 5 carbon atoms includes cyclic carbonates or chain carbonates having 3 to 5 carbon atoms, wherein the cyclic carbonates include but are not limited to at least one of ethylene carbonate (EC), vinylene carbonate (VC), vinylethylene carbonate (VEC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonates may specifically be but are not limited to dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC).

[0068] Preferably, the carboxylic acid ester having 2 to 6 carbon atoms includes, but is not limited to, at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, and propyl propionate (PP). As a preferred embodiment, the secondary battery non-aqueous electrolyte further includes vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or fluoroethylene carbonate (FEC).

[0069] Preferably, the ether solvent having 4 to 10 carbon atoms includes cyclic ethers or chain ethers having 4 to 10 carbon atoms, and the cyclic ethers include but are not limited to at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ethers include but are not limited to at least one of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (TEGDME).

[0070] In some embodiments, the positive electrode active material layer includes a positive electrode active material, wherein the positive electrode active material is selected from at least one of a layered transition metal oxide, a Prussian compound, a phosphate compound, and a sulfate compound;

[0071] The negative electrode includes a negative electrode active material, which includes one or more carbon-based materials, silicon-based materials, and tin-based materials. The carbon-based material includes at least one of hard carbon, soft carbon, carbon nanotubes, graphite, graphene, expanded graphite, and mesocarbon microbeads.

[0072] In some embodiments, the chemical formula of the layered transition metal oxide compound is Na n L m O r , 0<n≤1, 0<m≤1, 1<r≤2, L can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0073] In a preferred embodiment, the chemical formula of the layered transition metal oxide is Na p Ni m Mn n M (1-m-n) O q , where 0<p≤1, 0≤m<1, 0<m+n<1, 1<q≤2.

[0074] In a more preferred embodiment, the positive electrode active material is Na p＇ Ni m＇ Mn n＇ Fe (1-m＇-n＇) O2, wherein 0<p'≤1, 0≤m'<1, 0<m'+n'<1, 1<q'≤2. Further, NaNi is preferred. 0.3 Mn 0.3 Fe 0.4 O2、NaNi 0.4 Mn 0.4 Fe 0.2 O2、NaNi 0.5 Mn 0.35 Fe0.15 O2.

[0075] In a more preferred embodiment, the chemical formula of the layered transition metal oxide is NaNi m Co n Mn p At least one of O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1).

[0076] In some embodiments, the molecular formula of the Prussian compound is Na x＇ M[M′(CN)6] y＇ ·z'H2O, M is a transition metal, M' is a transition metal, 0 <x'≤2,0<y'≤1,0<z'≤20。

[0077] In a more preferred embodiment, the Prussian compound is Na x＇ Mn[Fe(CN)6] y＇ ·z'H2O or Na x＇ Fe[Fe(CN)6] y＇ ·z'H2O, 0<x'≤2, 0<y'≤1, 0<z'≤20.

[0078] In some embodiments, the chemical formula of the phosphate compound is Na3(RO 1-x＇＇ PO4)2F 1+2x＇＇ Or Na2R′PO4F, wherein 0≤x′′≤1, R is selected from at least one of Al, V, Ge, Fe, and Ga, and R′ is selected from at least one of Fe and Mn.

[0079] In a more preferred embodiment, the chemical formula of the phosphate compound is Na3(VPO4)2F3, Na3(VOPO4)2F, Na2FePO4F, or Na2MnPO4F.

[0080] In some embodiments, the chemical formula of the sulfate compound is Na2A(SO4)2·2H2O, where A is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0081] The present invention is further described below with reference to the following examples.

[0082] Example 1

[0083] This embodiment is used to illustrate the sodium ion battery disclosed in this application.

[0084] (1) Preparation of positive electrode: Prepare the positive electrode active material NaNi according to the mass ratio of 88.825:6.175:2:3 0.3 Fe0.3 Mn 0.4 O2, a sodium supplement additive Na5NbO5, conductive carbon black Super-P, and a binder polyvinylidene fluoride (PVDF) are mixed and then dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry. The resulting slurry is evenly coated on both sides of an aluminum foil, dried, rolled, and vacuum-dried, and then welded with aluminum lead wires using an ultrasonic welder to produce a positive electrode sheet. The mass content of the sodium supplement additive is a, and a is 6.5%, based on the total mass of the positive electrode active material and the sodium supplement additive as 100%.

[0085] (2) Preparation of the negative electrode: The negative electrode active material hard carbon, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in an appropriate amount of deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, rolled, and vacuum-dried, and then welded with nickel lead wires using an ultrasonic welder to obtain a negative electrode sheet. The particle size of the negative electrode active material hard carbon is c, and the specific value of c is shown in Table 1.

[0086] (3) Preparation of electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate were mixed in a mass ratio of EC:PC:EMC=10:15:75, followed by the addition of 12% by mass of sodium hexafluorophosphate, a sodium salt additive of sodium difluorooxalatoborate with a mass content b, and 1,3-propane sultone (PS), and finally, auxiliary additives to form an electrolyte. The specific types and mass contents of the auxiliary additives, the specific value of b, and the mass content of 1,3-propane sultone are shown in Table 1.

[0087] (4) Preparation of sodium ion battery: A separator is placed between the positive electrode sheet and the negative electrode sheet prepared above, and then a sandwich structure consisting of the positive electrode sheet, the negative electrode sheet and the separator is wound, and then the wound body is flattened and placed in an aluminum foil packaging bag to assemble a battery.

[0088] Examples 2-31 and Comparative Examples 1-11

[0089] Examples 2-31 and Comparative Examples 1-11 differ from Example 1 in the values ​​of a, c, and b, the type and mass content of the auxiliary additive, and the mass content of 1,3-propane sultone, as shown in Table 1. The preparation method is otherwise the same as in Example 1. The auxiliary additives, DTD, are vinyl sulfate, and RPS are acrylic lactone.

[0090] Table 2 Parameters of Examples and Comparative Examples

[0091] Performance Testing

[0092] The sodium ion batteries prepared in the above examples and comparative examples were subjected to the following performance tests.

[0093] 1. First effect test:

[0094] Place the battery at 25°C for 2 hours, charge it at a constant current rate of 0.5C to 4.0V, then charge it at a constant voltage rate to a current of 0.03C. Record the charge capacity, C1. Discharge it at a constant current rate of 1C to 1.5V, and record the discharge capacity, C2. Initial efficiency (%) = C2 / C1 × 100%.

[0095] 2. High temperature cycle performance test:

[0096] After formation, the battery was placed at 45°C for 2 hours, then charged at a constant current rate of 0.5C to 4.0V. Then, it was charged at a constant voltage rate to a current of 0.03C. The battery was discharged at a constant current rate of 1C to 1.5V. The discharge capacity (C3) at the first cycle was recorded. After 400 cycles of charge and discharge, the discharge capacity (C4) at the 400th cycle was recorded. The capacity retention (%) after 400 cycles of high-temperature cycling was calculated as: C4 / C3 × 100%.

[0097] Battery gas production was measured by converting the weight of displaced liquid into gas production. During the first cycle of charge and discharge, after the battery was fully charged, the weight of displaced liquid (G1) was measured and recorded. After the battery was fully charged for the 400th cycle, the weight of displaced liquid (G2) was measured and recorded. Gas production (mL) after 400 cycles of high-temperature cycling = G2 - G1.

[0098] 3. Normal temperature cycle performance test:

[0099] After formation, the battery was placed at 25°C for 2 hours. Charged at a constant current rate of 0.5C to 4.0V, then charged at a constant voltage rate to a current of 0.03C. Discharged at a constant current rate of 1C to 1.5V, recording the discharge capacity (C3) in the first cycle. After 400 cycles of charge and discharge, record the discharge capacity (C4) at the 400th cycle. Capacity retention (%) after 400 cycles at room temperature = C4 / C3 × 100%.

[0100] 4. Conductivity test:

[0101] Conductivity testing follows the HG / T 4067-2015 standard. The conductivity meter used is a DDSJ-308A with a range of 0.000 μS / cm to 199.9 mS / cm. Type 1 and Type 10 electrodes (platinum black) are used. Before use, calibration is performed using a 25°C potassium chloride standard solution: C(KCl) = 0.1 mol / l (standard value 12.88 mS / cm). During testing, the electrodes and temperature sensor are inserted into a beaker containing electrolyte. The beaker is then placed in a thermostatic bath and heated to 25°C. The reading is then read after the display stabilizes.

[0102] 5. DCIR test after battery capacity division

[0103] At 25°C, the battery is left for 5 minutes, then charged at a constant current rate of 1C to the upper cutoff voltage. Then, it is charged at a constant voltage until the current is less than or equal to 0.05C, at which point the battery's state of charge (SOC) is 100%. After that, it is left for 5 minutes, then discharged at a constant current rate of 1C to adjust the sodium-ion secondary battery's state of charge (SOC) to 50%. After 30 minutes of rest, it is discharged at a rate of 1C for 10 seconds. The voltage before discharge is recorded as U1, and the voltage after discharge is recorded as U2. The battery's DCIR = (U1-U2) / 1C.

[0104] 6. Battery internal resistance

[0105] After the battery is fully charged for the first time, the internal resistance of the battery is tested. Specifically, at 25°C, the battery is charged at a constant current rate of 1C to the upper cut-off voltage, and then charged at a constant voltage until the current is less than or equal to 0.05C. At this time, the state of charge (SOC) of the battery is 100%, and the internal resistance of the battery is tested.

[0106] The test results are shown in Table 2-5.

[0107] Table 2 Performance data of Examples 1-17 and Comparative Examples 1-11

[0108] It can be seen from Tables 1 and 2 that, when Example 1 is compared with Comparative Examples 1-3, there is no sodium-supplementing additive or sodium salt-type additive in Comparative Example 1, and the battery first efficiency is low, the internal resistance is high, and the cycle performance is poor; sodium-supplementing additive is added in Comparative Example 2, and the battery first efficiency is slightly improved, but the battery performance is still poor; there is no sodium-supplementing additive in Comparative Example 3, and sodium salt-type additive is added to the electrolyte, and the conductivity of the electrolyte is improved, but the battery first efficiency is low, the internal resistance is high, and the cycle performance is poor; this shows that adding sodium-supplementing additives to the battery can play a role in sodium supplementation and improve the battery first efficiency; adding sodium salt-type additives helps to improve the conductivity of the electrolyte. When Example 7 is compared with Comparative Examples 4-5, the mass content a of the sodium-supplementing additive added to the battery is less than 5%, and the battery first efficiency is low. The mass content a of the sodium-supplementing additive added is greater than 10%, and the battery first efficiency is low, the DCIR is high, the internal resistance is high, and the cycle performance is poor. It is speculated that the mass content a of the sodium-supplementing additive added to the battery is greater than 10%, and the sodium-supplementing additive decomposes, and the residual byproducts will destroy the interface film, increase the battery internal resistance, and reduce the battery first efficiency and cycle performance. Comparing Example 1 with Comparative Examples 5-6, the mass content b of the sodium salt type sodium supplement additive in the electrolyte is less than 1%, the conductivity of the electrolyte is low, and the internal resistance of the battery increases. When b is greater than 10%, although the electrolyte conductivity is improved, the internal resistance of the battery is high and the cycle performance is poor. It is speculated that adding a sodium salt type sodium supplement additive b between 1% and 10% to the electrolyte can improve the conductivity of the electrolyte and participate in the formation of the electrode interface film, protecting the positive and negative electrodes, and effectively solving the problem of poor conductivity of the sodium supplement additive and the damage of the positive and negative electrodes to the residual byproducts. Comparing Examples 6-7 with Comparative Examples 8-9, the particle size c of the negative active material is less than 2μm or c is greater than 12μm. The battery has low first efficiency, high DCIR, high internal resistance, low cycle capacity retention rate, and high gas production. Comparing Examples 1-17 with Comparative Examples 10-11, although the mass content a of the sodium supplement additive is between 5% and 10%, the mass content of the sodium salt additive b is between 1% and 10%, and the particle size c of the negative electrode active material is between 2 and 12 μm, the values ​​of a, b, and c do not satisfy the relationship 0.3≤a / (b+c)≤1.5. The battery has low first efficiency, poor cycle performance, high internal resistance, and high DCIR test impedance after battery capacity division. This indicates that a, b, and c in the battery must not only satisfy 5≤a≤10, 1≤b≤10, and 2≤c≤12, but also 0.3≤a / (b+c)≤1.5. Only in this way can the conductivity of the electrolyte and the diffusion and transmission rate of ions in the negative electrode material be effectively improved while ensuring the optimal conductivity of the positive electrode, thereby effectively reducing the overall internal resistance of the battery and improving the first efficiency and cycle performance of the battery.

[0109] By comparison of Examples 1-4, it can be seen that in the battery, taking the total mass of the positive electrode active material and the sodium supplement additive as 100%, the mass content of the sodium supplement additive is a, and a is in the range of 5.5% to 9%. The first efficiency of the battery is high, the capacity retention rate of normal temperature cycle and high temperature cycle is high, and the internal resistance of the battery is low. By comparison of Examples 5-9, it can be seen that the mass content b of the added sodium salt type additive in the electrolyte is between 2% and 6%. While the electrolyte has a relatively high conductivity, the internal resistance of the battery is low and the cycle capacity retention rate is high. By comparison of Examples 10-13, it can be seen that the particle size c of the negative electrode active material in the battery is in the range of 3 to 9 μm, the first efficiency of the battery is high, the DCIR is low, the cycle capacity retention rate is high, the gas production is low, and the internal resistance is low. By comparison with Examples 1-17, the values ​​of a, b, and c in the battery satisfy the range of 5≤a≤10, 1≤b≤10, 2≤c≤12, and satisfy 0.5≤a / (b+c)≤1.2. The battery has higher first efficiency and cycle performance, and the battery internal resistance is also lower.

[0110] Comparing Example 1 with Example 17, the electrolyte of Example 17 does not contain 1,3-propane sultone additive, the battery cycle capacity retention rate is low, the gas production is high, and the first efficiency is low, indicating that the addition of 1,3-propane sultone (PS) to the electrolyte can effectively inhibit the occurrence of side reactions on the positive electrode surface and the dissolution and precipitation of metal ions, stabilize the positive electrode crystal structure, effectively reduce the battery internal resistance and gas production, and improve the cycle performance.

[0111] Table 3 Battery performance data of Example 1 and Examples 18-21

[0112] As shown in Tables 1 and 3, when different types of sodium supplement additives are added to the battery, the first efficiency, internal resistance, DCIR, cycle capacity retention rate and gas production of the battery are basically similar, indicating that as long as the sodium supplement additives meet the requirements of Na x M y O z The compound shown in Formula 1, wherein 0.2<x / y<9, 0<y<6, 2≤z≤9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr, all have the effects of improving the first efficiency and cycle performance of the battery and reducing the internal resistance of the battery.

[0113] Table 4 Battery performance data of Example 1 and Examples 22-23

[0114] It can be seen from Tables 1 and 4 that, when Example 1 is compared with Examples 22-23, different types of sodium salt additives are added to the electrolyte, and the first efficiency, internal resistance, DCIR, cycle capacity retention rate and gas production of the battery are basically similar, indicating that the different types of sodium salt additives provided in this application have the effect of improving the first efficiency and cycle performance of the battery and reducing the internal resistance of the battery.

[0115] Table 5 Battery performance data of Example 1 and Examples 24-31

[0116] As shown in Tables 1 and 5, when comparing Example 1 with Examples 24-28, the 1,3-propane sultone added to the electrolyte and the 1,3-propane sultone added to Examples 27-28 are not within the range of 0.5% to 2%, the battery has a high DCIR, high internal resistance, high gas production, and low cycle capacity retention. This indicates that adding 1,3-propane sultone (PS) to the electrolyte at a mass content of 0.5% to 2% can effectively inhibit the occurrence of electrode surface side reactions and the dissolution and precipitation of metal ions on the positive electrode surface, stabilize the positive electrode crystal structure, effectively reduce the battery internal resistance and gas production rate, and improve cycle performance. When the PS content added to the electrolyte is within the range of 1% to 2%, the battery internal resistance and gas production are relatively low.

[0117] Comparing Example 1 with Examples 29-30, 1,3-propane sultone and auxiliary additives were added to the electrolyte of Examples 29-30, and the DCIR and internal resistance of the battery were reduced, the cycle gas production was greatly reduced, the first efficiency was increased, and the cycle capacity retention rate was improved. This shows that the addition of 1,3-propane sultone to the electrolyte, in synergy with the auxiliary additives, has the effect of reducing the DCIR, internal resistance and gas production of the battery, and improving the first efficiency and cycle performance of the battery.

[0118] 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 non-aqueous electrolyte, a positive electrode and a negative electrode, wherein the non-aqueous electrolyte comprises an additive, wherein the additive comprises a sodium salt type additive, the positive electrode comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises a sodium supplement additive and a positive electrode active material, wherein the sodium supplement additive is a sodium-rich transition metal oxide; the negative electrode comprises a negative electrode active material, The sodium ion battery satisfies the following relationship: 0.3≤a / (b+c)≤1.5, and 5≤a≤10, 1≤b≤10, 2≤c≤12; Wherein, the total mass of the sodium supplement additive and the positive electrode active material is 100%, a is the mass content of the sodium supplement additive, unit %; b is the mass content of the sodium salt type additive in the non-aqueous electrolyte, in %; c is the particle size of the negative electrode active material, in μm.

2. The sodium ion battery according to claim 1, characterized in that The sodium ion battery satisfies the following relationship: 0.5≤a / (b+c)≤1.

2.

3. The sodium ion battery according to claim 1, characterized in that: The total mass of the sodium supplement additive and the positive electrode active material is 100%, and the mass content a of the sodium supplement additive is in the range of 5.5% to 9%.

4. The sodium ion battery according to claim 1, characterized in that The sodium salt additive includes one or more of sodium bis(fluorosulfonyl)imide, sodium difluorooxalatoborate, and sodium difluorophosphate.

5. The sodium ion battery according to claim 1, characterized in that: The mass content b of the sodium salt additive in the non-aqueous electrolyte is in the range of 2% to 6%.

6. The sodium ion battery according to claim 1, characterized in that: The particle size c of the negative electrode active material is in the range of 3 μm to 9 μm.

7. The sodium ion battery according to claim 1, characterized in that: The additive further comprises 1,3-propane sultone, and the mass content of the 1,3-propane sultone in the non-aqueous electrolyte is 0.5% to 2%.

8. The sodium ion battery according to claim 7, characterized in that: The mass content of the 1,3-propane sultone in the non-aqueous electrolyte is 1% to 2%.

9. The sodium ion battery according to claim 1, characterized in that: The sodium-rich transition metal oxide comprises a compound shown in Formula 1, Na x M y O z Formula 1, Among them, 0.2<x / y<9, 0<y<6, 2≤z≤9, and M is selected from one or more of Nb, V, Ta, Mn, Fe, Cr, Co, Ni, Cu, Zn, Mg, Ti, Si, Sn, Ce, and Zr.

10. The sodium ion battery according to claim 9, characterized in that: The sodium-rich transition metal oxide includes one or more of Na5NbO5, Na3NbO4, Na4Nb2O7, Na5VO5, Na3VO4, and Na3TaO4.

11. The sodium ion battery according to claim 1, characterized in that: The non-aqueous electrolyte further comprises an electrolyte salt, an auxiliary additive and a non-aqueous organic solvent. The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium trifluoromethylsulfonyl imide, sodium trifluoromethylsulfonate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium trifluoroacetate, sodium tetraphenylborate and sodium bis(trifluoromethylsulfonyl)imide; The mass content of the electrolyte salt is 8% to 14% based on the mass of the electrolyte solution being 100%; The auxiliary additive includes at least one of 1,4-butane sultone, acrylic acid lactone, vinyl sulfate and fluoroethylene carbonate; Taking the mass of the electrolyte as 100%, the mass content of the auxiliary additive is 2.5% to 10%; The non-aqueous organic solvent includes at least one of carbonates having 3 to 5 carbon atoms, carboxylates having 2 to 6 carbon atoms, and ethers having 4 to 10 carbon atoms.

12. The sodium ion battery according to claim 1, characterized in that: The positive electrode active material includes at least one of a layered transition metal oxide, a Prussian compound, a phosphate compound, and a sulfate compound; The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes one or more of a carbon-based material, a silicon-based material, and a tin-based material.

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