A sodium ion battery

Abstract

The present invention relates to the field of electrochemical technology, and in particular to a sodium ion battery comprising a positive electrode, a negative electrode, and an electrolyte; the discharge capacity curve of the negative electrode undergoing a charge-discharge test corresponds to a slope region capacity ratio A and a plateau region capacity ratio B that satisfy the following conditions: 0.66 ≤ A / B ≤ 2.34; the electrolyte comprises NaFSI, and the mass percentage C of NaFSI relative to the electrolyte satisfies the following conditions: 1% ≤ C ≤ 15%. The sodium ion battery of the present invention can ensure sufficient negative electrode capacity by regulating the ratio of the plateau region capacity to the slope region capacity of the negative electrode active material, stabilize the positive and negative electrode capacity release ratio, and allow Na to be released from the positive electrode. + Can be fully embedded in the negative electrode to prevent Na + It precipitates at the negative electrode, effectively inhibiting the occurrence of sodium precipitation. At the same time, the electrolyte uses NaFSI and controls the content range. While improving the conductivity of the electrolyte, the film formation stability on the positive and negative sides of the battery is good, and the current collector is not corroded, effectively improving the battery's rate performance and cycle stability.

Description

Technical Field

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

[0002] Due to the rapid growth in demand for clean energy, secondary battery technology is developing rapidly, with sodium-ion batteries, a particular area of focus due to their abundant raw material resources. Similar in principle and structure to lithium-ion batteries, sodium-ion batteries offer a wide range of resources, low cost, and minimal fluctuation compared to lithium-ion batteries. Their wide temperature range and high safety performance offer potential as a potential alternative. With the continuous advancement of sodium-ion battery technology, sodium-ion batteries have broad potential for growth in the energy storage sector. Therefore, the development of high-performance, low-cost sodium-ion batteries is a crucial factor in determining their industrialization.

[0003] However, compared to lithium-ion batteries, sodium-ion batteries still have problems with low energy density and insufficient cycle life. At the same time, the high rate and ultra-low temperature discharge performance of sodium-ion batteries are their important advantages over lithium-ion batteries. Therefore, improving the long cycle life and high rate performance of sodium-ion batteries is a key issue in the current research of the sodium-ion battery industry. Since the negative electrode uses carbon-based materials other than graphite, the current research focus of the industry is on how to improve the film formation quality of the negative electrode SEI film to improve the performance of the battery. However, there is less research on the influence of the intrinsic properties of the negative electrode material (such as microstructure composition / particle size / specific surface area, etc.) on battery performance. At the same time, NaFSI is a very promising additive and co-salt, but in research, there is a disadvantage of NaFSI corroding the current collector, deteriorating battery performance, thereby limiting its application in sodium-ion batteries and affecting the rate performance and cycle performance of sodium-ion batteries. Summary of the Invention

[0004] In response to the above technical problems, the present invention provides a sodium ion battery to overcome the problems of insufficient cycle performance and poor rate performance of sodium ion batteries in the prior art.

[0005] The present invention adopts the following technical solutions:

[0006] A sodium ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises an electrolyte salt, an electrolyte additive and a solvent;

[0007] The slope area capacity ratio A and the platform area capacity ratio B corresponding to the discharge capacity curve of the negative electrode subjected to the power-off test satisfy the following relationship:

[0008] 0.66≤A / B≤2.34

[0009] The ramp area capacity ratio A is the capacity release ratio in the 3.0-0.1V voltage range of the power-off test, and the platform area capacity ratio B is the capacity release ratio in the 0.1-0V voltage range of the power-off test, where A+B=1.

[0010] The electrolyte includes NaFSI (sodium bis(fluorosulfonyl)imide) as an electrolyte salt or electrolyte additive. Based on the total mass of the electrolyte being 100%, the mass percentage C of the amount of NaFSI relative to the electrolyte satisfies: 1%≤C≤15%.

[0011] Specifically, the capacity proportion A in the slope area is the capacity corresponding to the power-off test of 3.0-0.1V divided by the total capacity, and the capacity proportion B in the platform area is the capacity corresponding to the power-off test of 0.1-0V divided by the total capacity. The total capacity is the capacity of the power-off test of 3.0-0V.

[0012] After a large number of experimental studies, the inventors found that when the ratio between the capacity proportion A of the slope area and the capacity proportion B of the platform area meets the requirements within a specific range, and NaFSI is used as the electrolyte salt or electrolyte additive in the electrolyte, a full battery test was conducted and it was found that the battery overcomes the risk of NaFSI corrosion of the current collector while inhibiting the occurrence of sodium precipitation, thereby achieving the performance advantages of high capacity / high rate and long cycle.

[0013] The experiment found that when the ratio of the platform capacity to the slope capacity of the negative electrode material used in the battery satisfies 0.66≤A / B≤2.34, it can ensure that the negative electrode has sufficient capacity to play a role, stabilize the positive and negative electrode capacity release ratio, and make the Na released from the positive electrode + Can be fully embedded in the negative electrode to prevent Na + When A / B is less than 0.66, the negative electrode material capacity release is too low, resulting in sodium precipitation in the entire battery, deterioration and cycle, and increased battery safety risks. When A / B is greater than 2.34, the negative electrode material capacity release is also too low, resulting in sodium precipitation in the entire battery, deterioration and cycle, and increased battery safety risks.

[0014] Preferably, in some embodiments of the present invention, the capacity of the slope region and the platform region corresponding to the discharge capacity curve of the negative electrode during the power-off test satisfy the following relationship:

[0015] 0.81≤A / B≤1.63.

[0016] As an electrolyte salt or electrolyte additive, NaFSI can improve the conductivity, electrochemical, and thermal stability of the electrolyte, participate in the formation of the SEI film, reduce side reactions, effectively lower the impedance during battery cycling, and improve cycle performance. NaFSI's high conductivity ensures low concentrations in the electrolyte. Its high conductivity and high capacity effectively inhibit sodium precipitation, thereby ensuring long cycling times while also suppressing the occurrence of sodium precipitation.

[0017] The amount of NaFSI used relative to the mass percentage C of the electrolyte satisfies the following: 1% ≤ C ≤ 15%. Above this range, the viscosity of the electrolyte increases and corrodes the current collector, causing the active material of the electrode to fall off, seriously degrading the battery performance; below this range, the conductivity of the electrolyte is too low. Specifically, based on the total mass of the electrolyte as 100%, the amount of NaFSI used relative to the mass percentage C of the electrolyte can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. Preferably, in some embodiments of the present invention, based on the total mass of the electrolyte as 100%, the amount of NaFSI used relative to the mass percentage C of the electrolyte satisfies the following: 2% ≤ C ≤ 11%.

[0018] Furthermore, the negative electrode includes a negative electrode active material, and the negative electrode active material is a carbon material; the carbon material is selected from at least one of hard carbon and soft carbon.

[0019] Furthermore, the electrolyte salt includes one or more of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]) or sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]).

[0020] Furthermore, the solvent is selected from one or more of C3-C5 carbonate solvents, C2-C6 carboxylate solvents, and C4-C10 ether solvents;

[0021] Taking the total mass of the electrolyte as 100%, the mass percentage of the solvent relative to the electrolyte is 70-92%.

[0022] Specifically, in some embodiments of the present invention, the carbonate solvent includes a C3-C5 cyclic carbonate or a chain carbonate, the cyclic carbonate is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate is selected from one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC); the carboxylate solvent is selected from one or more of ethyl propionate (EP), methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, and propyl carbonate. one or more of propyl carboxylate (PP); the ether solvent includes a C4-C10 cyclic ether or chain ether, the cyclic ether is selected from one or more of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether is selected from one or more of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (TEGDME), ethylene glycol diethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0023] Furthermore, the electrolyte additive is selected from one or more of cyclic carbonate compounds, fluorinated cyclic carbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, phosphate compounds, borate compounds and nitrile compounds;

[0024] Preferably, the cyclic carbonate compound is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, and methylene carbonate;

[0025] The fluorinated cyclic carbonate compound is selected from one or more of fluoroethylene carbonate and difluoroethylene carbonate;

[0026] The cyclic sulfonate compound is selected from one or more of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone;

[0027] The cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate;

[0028] The phosphate compound is selected from one or more of tripropargyl phosphate, trimethyl phosphate, triethyl phosphate, and tris(trimethylsilyl) phosphate;

[0029] The borate compound is selected from one or more of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;

[0030] The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0031] Based on the total mass of the electrolyte being 100%, the mass percentage of the electrolyte additive relative to the electrolyte is 1-5%.

[0032] Furthermore, the positive electrode includes a positive electrode active material, and the positive electrode active material is selected from one or more of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

[0033] Specifically, in some embodiments of the present invention, the chemical formula of the layered transition metal oxide is Na x M y O z , 0<x≤1, 0<y≤1, 1<z≤2, M can be selected from one or more of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V; the transition metal oxide is NaNi m Fe n Mn p O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1), NaNi m Co n Mn p O2 (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1); More specifically, the layered transition metal oxide is selected from Na[Cu 1 / 9Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 ]O2、Na 0.44 MnO2、Na 2 / 3 [Fe 1 / 2 Mn 1 / 2 ]O2、Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 ]O2、Na 7 / 9 [Cu 2 / 9 Fe 1 / 9Mn 2 / 3 ]O2、NaNi 0.7 Co 0.15 Mn 0.15 One or more of O2.

[0034] In some embodiments of the present invention, the molecular formula of the Prussian compound is Na x M[M′(CN)6] y·zH2O, where M is a transition metal, M' is a transition metal, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; the Prussian compound is Na x Mn[Fe(CN)6] y ·nH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20), the Prussian compound is Na x Fe[Fe(CN)6] y ·nH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20).

[0035] In some embodiments of the present invention, the chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, and M is selected from one or more of Al, V, Ge, Fe, Ga; the chemical formula of the phosphate compound is Na3(VPO4)2F3, Na3(VOPO4)2F.

[0036] In some embodiments of the present invention, the chemical formula of the phosphate compound is Na2MPO4F, and M is selected from one or more of Fe, Mn; the chemical formula of the phosphate compound is Na2FePO4F, Na2MnPO4F.

[0037] In some embodiments of the present invention, the chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, and M can be selected from one or more of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

[0038] Furthermore, the negative electrode further includes a negative electrode conductive agent, and the negative electrode conductive agent is selected from one or more of acetylene black, SuperP, graphene, Ketjen black, SFG-6, carbon nanotubes, graphdiyne.

[0039] Furthermore, the negative electrode further includes a negative electrode binder, and the negative electrode binder is selected from one or more of polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimides, thermoplastic resins such as polyethylene and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0040] Furthermore, the positive electrode further includes a positive electrode conductor and a positive electrode binder. The positive electrode binder and the positive electrode conductor may be the same as the negative electrode binder and the negative electrode conductor, respectively, and are not described in detail herein.

[0041] In some embodiments of the present invention, the positive electrode or negative electrode is prepared by uniformly mixing an active material, a binder, a conductive agent, and a solvent, coating the mixture on a substrate, and removing the solvent to obtain the positive electrode or negative electrode.

[0042] In some embodiments of the present invention, the sodium ion battery further includes a diaphragm, and the diaphragm is located between the positive electrode and the negative electrode.

[0043] 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.

[0044] In some embodiments of the present invention, the preparation method of the sodium ion battery is a general preparation method for secondary batteries, that is, the positive electrode, the separator, and the negative electrode are combined, and the electrolyte is injected to obtain the sodium ion battery.

[0045] Compared with the prior art, the present invention achieves the following beneficial effects:

[0046] The sodium ion battery of the present invention can ensure sufficient capacity of the negative electrode by regulating the ratio of the platform area capacity ratio and the slope area capacity ratio of the negative electrode active material used in the battery, stabilize the positive and negative electrode capacity release ratio, and make the Na released from the positive electrode + Can be fully embedded in the negative electrode to prevent Na + It precipitates at the negative electrode, effectively inhibiting the occurrence of sodium precipitation; at the same time, the electrolyte used uses NaFSI as the electrolyte salt or additive and controls the content range of NaFSI, which improves the conductivity of the electrolyte while ensuring good film formation stability on the positive and negative electrode sides of the battery, and the current collector does not corrode, effectively improving the battery's rate performance and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0048] Figure 1 This is a charge and discharge curve diagram of the negative electrode of the present invention. DETAILED DESCRIPTION

[0049] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0050] Adjustment method of platform area capacity and slope area capacity:

[0051] In the present invention, the slope region capacity A and the plateau region capacity B are obtained by performing a button-type half-cell test on the negative electrode. The specific steps are as follows:

[0052] (1) Using the LAND test system, the negative electrode was tested. First, it was discharged to 0 V at a current density of 0.1 C, with a voltage range of 0-3.0 V, to obtain a discharge capacity of 1. After standing for 10 minutes, it was charged to 3.0 V at a current density of 0.1 C, to obtain a charge capacity of 2.

[0053] (2) According to the procedure of step (1), the discharge and charge curves of the negative electrode can be obtained. During discharge, the voltage-capacity curve when discharged to 0V is the platform region and slope region curve in the present invention, see Figure 1 .

[0054] In the present invention, the slope zone capacity A and the platform zone capacity B corresponding to the discharge capacity curve of the negative electrode subjected to the power-off test using the above method satisfy the relationship: 0.66≤A / B≤2.34, wherein the slope zone capacity A is the capacity release ratio in the power-off test voltage range of 0.1-3.0V, and the platform zone capacity B is the capacity release ratio in the power-off test voltage range of 0.1-0V, and A+B=1.

[0055] In the present invention, the method for regulating the slope zone capacity and the platform zone capacity in the negative electrode charge-withdrawal test is as follows: by controlling the particle size of the negative electrode active material particles in the negative electrode of the sodium ion battery of the present invention, the amount of the conductive agent in the negative electrode, and the amount of the negative electrode film-forming additive in the electrolyte, the ratio (A / B) of the slope zone capacity A and the platform zone capacity B can be controlled.

[0056] Among them, when the particle size of the negative electrode active material satisfies 4μm≤d50≤8μm, the mass content of the conductive agent in the negative electrode plate is 1%~5%, and the mass content of the negative electrode film-forming additive in the electrolyte is 1%~5%, it is possible to achieve the regulation of the slope zone capacity A and the platform zone capacity B to satisfy the relationship: 0.66≤A / B≤2.34.

[0057] During the course of experiments, the inventors discovered that the relationship between the negative electrode active material particle size, the amount of negative electrode conductive agent, and the amount of negative electrode film-forming additive in the electrolyte and the ratio of the slope region capacity A to the plateau region capacity B (A / B) is as follows: as the negative electrode active material particle size and the amount of negative electrode film-forming additive increase, the negative electrode surface defects and pores increase, and the A / B ratio increases; as the amount of negative electrode conductive agent increases, sodium ions are more easily embedded in the negative electrode, and the A / B ratio decreases. The relationship between the negative electrode active material particle size d50, the amount of conductive agent in the negative electrode, and the amount of negative electrode film-forming additive in the electrolyte and A / B can be summarized in Table 1.

[0058] Table 1

[0059]

[0060]

[0061] For example, examples of regulating the A / B ratio by controlling the particle size d50 of the negative electrode active material particles, the amount of the negative electrode conductive agent, and the amount of the negative electrode film-forming additive in the electrolyte can be seen in Table 2.

[0062] Table 2

[0063]

[0064] Examples 1-18

[0065] The present invention provides a sodium ion battery comprising a positive electrode, a negative electrode and an electrolyte.

[0066] (1) Preparation of electrolyte

[0067] Ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a mass ratio of 2:1:7. Based on the total weight of the electrolyte being 100%, NaFSI in the mass percentages shown in Table 3, as well as 5.6% sodium hexafluorophosphate (NaPF6) and 2% of fluorinated ethylene carbonate as a negative electrode film-forming additive were added.

[0068] (2) Preparation of positive electrode plate

[0069] The positive electrode active material NaNi was prepared in a mass ratio of 93:4:3. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) are mixed and then dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to obtain positive electrode slurry; the obtained slurry is evenly coated on both sides of aluminum foil, dried, rolled and vacuum dried, and aluminum lead wires are welded with an ultrasonic welder to obtain a positive electrode plate with a thickness of 120-150μm.

[0070] (3) Preparation of negative electrode plate

[0071] 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 plate with a thickness of 120-150 μm. The ratio A / B of the capacity proportion A of the slope region to the capacity proportion B of the platform region in the hard carbon is shown in Table 3.

[0072] (4) Preparation of battery cells

[0073] A three-layer separator with a thickness of 20 μm was placed between the positive plate and the negative plate prepared above. The sandwich structure consisting of the positive plate, the negative plate and the separator was then wound. The wound body was flattened and placed in an aluminum foil packaging bag. The battery was vacuum-baked at 75°C for 48 hours to obtain a battery cell ready for liquid injection.

[0074] (5) Battery injection and formation

[0075] In a glove box with a dew point controlled below -40°C, the prepared electrolyte was injected into the battery cell, vacuum-sealed, and left to stand for 24 hours.

[0076] The conventional charging formation is then carried out according to the following steps: 0.05C constant current charging for 180 minutes, 0.2C constant current charging to 3.95V, secondary vacuum sealing, and then further 0.2C constant current charging to 4.2V, after being placed at room temperature for 24 hours, and then 0.2C constant current discharge to 3.0V to obtain a sodium ion battery.

[0077] Comparative Examples 1-5

[0078] Comparative Examples 1-5 include most of the operating steps in the above embodiments, except that: during the preparation of the electrolyte, NaFSI in the mass percentage shown in Comparative Examples 1-5 in Table 1 was added, based on 100% of the total mass of the electrolyte, and the negative electrode active material having the values of the slope region capacity proportion A and the platform region capacity proportion B and the ratio A / B shown in Comparative Examples 1-5 in Table 1 was added, and the test results were filled in Table 1.

[0079] Performance Testing

[0080] The sodium ion batteries prepared in Examples 1-18 and Comparative Examples 1-5 were subjected to the following performance tests:

[0081] 25°C electrolyte conductivity test: The prepared electrolytes were tested using a conductivity meter at 25°C.

[0082] Sodium precipitation test: At 25°C, the battery was charged at a constant current of 1C and a constant voltage of 3.95V, followed by a charge cutoff of 0.03C and a discharge cutoff of 1C / 1.5V. After 50 cycles, the battery was disassembled and its effectiveness in suppressing sodium precipitation at the negative electrode was evaluated.

[0083] 4C rate discharge capacity ratio: the ratio of the capacity released by the battery from 3.95-1.5V at a 4C rate to the capacity released by the battery at a 0.2C rate during the activation stage.

[0084] High temperature / normal temperature cycle test: The formed battery was placed at 45℃ / 25℃ for 2h, charged at a constant current rate of 0.5C to 3.9V, then charged at a constant voltage to a current of 0.03C, and then discharged at a constant current of 1C to 1.5V, for 200 cycles;

[0085] Capacity retention rate (%)=(discharge capacity C2-charge capacity C1) / charge capacity C1×100%.

[0086] The test results are shown in Table 3.

[0087] Table 3

[0088]

[0089]

[0090]

[0091] It can be seen from the test results of Examples 1-18 that when the ratio of the capacity proportion of the platform area to the capacity proportion of the slope area of the battery negative electrode material satisfies 0.66≤A / B≤2.34, it can ensure that the negative electrode has sufficient capacity to play, stabilize the positive and negative electrode capacity release ratio, and make the Na released from the positive electrode + Can be fully embedded in the negative electrode to prevent Na +Precipitation at the negative electrode is effective in suppressing the risk of sodium precipitation in the battery; at the same time, controlling the amount of NaFSI in the electrolyte helps to improve the cycle performance of the sodium ion battery, improve the rate performance and suppress the risk of sodium precipitation, and improve the safety performance of the battery. It can be seen from the test results of Examples 1-10 and Comparative Examples 1-2 that when the ratio A / B of the platform area capacity ratio to the slope area capacity ratio is too high or too low, in addition to causing the occurrence of sodium precipitation, it will also lead to a decrease in battery rate and cycle performance. This is because the platform area capacity and the slope area capacity can control the sodium ion storage mechanism in the negative electrode material to a certain extent, but the degree of reduction is less than the effect of NaSFI. It can be seen from the test results of Examples 11-18 and Comparative Examples 3-5 that a certain amount of NaSFI as an electrolyte additive or electrolyte salt can improve the conductivity, electrochemical and thermal stability of the electrolyte, participate in the formation of SEI film, reduce side reactions, and effectively reduce the impedance during the battery cycle. When the NaSFI content is too high, the electrolyte viscosity increases and corrodes the current collector, causing the active material of the electrode to fall off, seriously deteriorating the battery performance; when the NaSFI content is too low, the electrolyte conductivity is too low.

[0092] In summary, the present invention provides a sodium ion battery, which can ensure sufficient capacity of the negative electrode by regulating the platform area capacity ratio and slope area capacity ratio of the negative electrode active material used in the battery, stabilize the positive and negative electrode capacity release ratio, and make the Na released from the positive electrode + Can be fully embedded in the negative electrode to prevent Na + It precipitates at the negative electrode, effectively inhibiting the occurrence of sodium precipitation; at the same time, the electrolyte used uses NaFSI as the electrolyte salt or additive and controls the content range of NaFSI, which improves the conductivity of the electrolyte while ensuring good film formation stability on the positive and negative electrode sides of the battery, and the current collector does not corrode, effectively improving the battery's rate performance and cycle stability.

[0093] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in this field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A sodium ion battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The electrolyte comprises an electrolyte salt, an electrolyte additive and a solvent; The slope area capacity ratio A and the platform area capacity ratio B corresponding to the discharge capacity curve of the negative electrode subjected to the power-off test satisfy the following relationship: 0.66≤A / B≤2.34 The ramp area capacity ratio A is the capacity release ratio in the 3.0-0.1V voltage range of the power-off test, and the platform area capacity ratio B is the capacity release ratio in the 0.1-0V voltage range of the power-off test, where A+B=1. The electrolyte includes NaFSI as an electrolyte salt or an electrolyte additive, and based on the total mass of the electrolyte being 100%, the mass percentage C of the amount of NaFSI relative to the electrolyte satisfies: 1%≤C≤15%; The negative electrode includes a negative electrode active material, and the particle size of the negative electrode active material satisfies 4μm≤d50≤8μm; The negative electrode further includes a conductive agent, the mass content of the conductive agent is 1% to 5%; The electrolyte includes a negative electrode film-forming additive, and the mass content of the negative electrode film-forming additive is 1% to 5%.

2. The sodium ion battery according to claim 1, characterized in that The slope area capacity ratio A and the platform area capacity ratio B corresponding to the discharge capacity curve of the negative electrode subjected to the power-off test satisfy the following relationship: 0.81≤A / B≤1.

63.

3. The sodium ion battery according to claim 1, characterized in that Based on the total mass of the electrolyte being 100%, the mass percentage C of the amount of NaFSI relative to the electrolyte satisfies: 2%≤C≤11%.

4. The sodium ion battery according to claim 1, characterized in that The negative electrode includes a negative electrode active material, and the negative electrode active material is a carbon material; The carbon material is selected from at least one of hard carbon and soft carbon.

5. The sodium ion battery according to claim 1, characterized in that The electrolyte salt includes one or more of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, or sodium bis(trifluoromethylsulfonyl)imide.

6. The sodium ion battery according to claim 1, characterized in that The solvent is selected from one or more of C3-C5 carbonate solvents, C2-C6 carboxylate solvents, and C4-C10 ether solvents; Taking the total mass of the electrolyte as 100%, the mass percentage of the solvent relative to the electrolyte is 70-92%.

7. The sodium ion battery according to claim 6, characterized in that: The carbonate solvent includes a C3-C5 cyclic carbonate or a chain carbonate, wherein the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; and the chain carbonate is selected from one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate. The C2-C6 carboxylic acid ester solvent is selected from one or more of ethyl propionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate; The ether solvent includes a C4-C10 cyclic ether or chain ether, the cyclic ether is selected from one or more of 1,3-dioxolane, 1,4-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ether is selected from one or more of dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

8. The sodium ion battery according to claim 1, characterized in that The electrolyte additive is selected from one or more of cyclic carbonate compounds, fluorinated cyclic carbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, phosphate compounds, borate compounds and nitrile compounds.

9. The sodium ion battery according to claim 8, characterized in that: The cyclic carbonate compound is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, and methylene carbonate; The fluorinated cyclic carbonate compound is selected from one or more of fluoroethylene carbonate and difluoroethylene carbonate; The cyclic sulfonate compound is selected from one or more of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone; The cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate; The phosphate compound is selected from one or more of tripropargyl phosphate, trimethyl phosphate, triethyl phosphate, and tris(trimethylsilyl) phosphate; The borate compound is selected from one or more of tris(trimethylsilyl)borate and tris(triethylsilyl)borate; The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

10. The sodium ion battery according to claim 8, characterized in that Based on the total mass of the electrolyte being 100%, the mass percentage of the electrolyte additive relative to the electrolyte is 1-5%.

11. The sodium ion battery according to any one of claims 1 to 10, characterized in that: The positive electrode includes a positive electrode active material, and the positive electrode active material is selected from one or more of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

12. The sodium ion battery according to claim 11, characterized in that: The chemical formula of the layered transition metal oxide is Na x M y O z , 0<x≤1, 0<y≤1, 1<z≤2, M is selected from one or more of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V; the transition metal oxide is NaNi m Fe n Mn p O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1), NaNi m Co n Mn p O2(m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1); The molecular formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, M is a transition metal, M' is a transition metal, 0 <x≤2,0<y≤1,0<z≤20; The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0≤x≤1, M is selected from one or more of Al, V, Ge, Fe, and Ga; The chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, where M is selected from one or more of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

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