Sodium ion battery

Abstract

The sodium ion battery comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, a sodium supplementing agent, a conductive agent and a binder, the sodium supplementing agent comprises NaxNiyOz, x is greater than or equal to 1 and less than or equal to 2, y is greater than or equal to 0 and less than or equal to 1, z is greater than or equal to 1 and less than or equal to 2, and the mass percentage content of the sodium supplementing agent in the positive electrode material layer is A; the upper limit voltage is B V; the electrolyte comprises a first solvent, a sodium salt and an additive, the first solvent comprises fluoroether, and the mass percentage content of the fluoroether in the electrolyte is C; a, B and C meet the relational expression that A * B / C is larger than or equal to 1.0 and smaller than or equal to 4.0. The first effect and cycle performance of the sodium ion battery can be improved at the same time by regulating and controlling the relation among the content of the fluoro-ether, the content of the nickel-based sodium supplement and the upper limit voltage.

Description

Technical Field

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

[0002] The rapid growth of the electrochemical energy storage market has promoted the rapid development of electrochemical energy storage devices such as sodium-ion batteries. The first efficiency is one of the key performances of secondary batteries. A higher first efficiency is conducive to improving the utilization rate of active materials and increasing the energy density of the battery. However, during the battery charging and discharging process, the formation of the negative electrode SEI film consumes a large amount of active sodium, resulting in an increase in irreversible capacity and a decrease in the first efficiency of the battery. There are many ways to supplement active sodium. For example, positive electrode sodium supplementation is to add a sodium supplement with a high irreversible capacity to the positive electrode of the sodium-ion battery to increase the capacity of the sodium-ion battery, thereby improving the battery's first coulombic efficiency. However, the commonly used sodium supplements are structurally unstable and prone to side reactions or self-decomposition. At higher reaction voltages, they are prone to chain decomposition of electrolyte solvents, and decomposition byproducts accumulate at the interface, leading to higher cycle gas production and deterioration of battery performance. Therefore, it is necessary to study how to improve the cycle performance of sodium-ion batteries while supplementing sodium and improve the first efficiency of the battery. Summary of the invention

[0003] The present invention is based on the inventors' discovery and understanding of the following facts and problems: the currently commonly used sodium supplements are structurally unstable and prone to side reactions or self-decomposition. Under higher reaction voltages, they are prone to chain breakage and decomposition of electrolyte solvents, and the decomposition by-products accumulate at the interface, leading to higher cycle gas production and deterioration of battery performance.

[0004] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, an embodiment of the present invention provides a sodium ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, a sodium supplement, a conductive agent and a binder, and the sodium supplement comprises Na x Ni y O z , wherein 1≤x≤2, 0≤y≤1, 1≤z≤2, and the mass percentage of the sodium supplement in the positive electrode material layer is A;

[0005] The upper voltage limit is BV;

[0006] The electrolyte comprises a first solvent, a sodium salt and an additive, wherein the first solvent comprises a fluoroether, and the mass percentage of the fluoroether in the electrolyte is C;

[0007] A, B, and C satisfy the relationship: 1.0≤A*B / C≤4.0.

[0008] Optional, A is 5%-10%.

[0009] Optional, B is 4.0-4.2.

[0010] Optionally, C is 10%-40%.

[0011] Optionally, the sodium supplement includes NaNiO2, Na2NiO2, Na 1.9 Ni 0.7 O2、Na 1.6 Ni 0.8 O2、Na 1.3 Ni 0.9 O2、NaNi 0.5 O、Na 1.2 Ni 0.4 O or Na 1.4 Ni 0.3 At least one of O.

[0012] Optionally, the fluoroether includes 1,2,3,3,4,4,5,5-octafluoropentyl methyl ether, 1,2,3,3,4,4,5,5-octafluoropentyl ethyl ether, 2,2,3,3,4,4,5-heptafluoropentyl methyl ether, 2,2,3,3,4,4,5-heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5-octafluoropentyl methyl ether, 2,2,3,3,4,4,5-heptafluoropentyl ethyl ether, , at least one of 1,2,2,3,3,4,4-heptafluorobutyl methyl ether, 2,2,3,3,4,4-hexafluorobutyl methyl ether, 2,2,3,3,4,4,5,5,6-nonafluorohexyl methyl ether, 2,2,3,3,4,4,5,5,6,6-decafluorohexyl methyl ether, and 2,2,3,3,4,4,5,5-octafluorohexyl methyl ether.

[0013] Optionally, the electrolyte further includes a second solvent; the second solvent includes at least one of a non-fluorine-substituted carbonate having 3 to 7 carbon atoms, a carboxylic acid ester having 2 to 6 carbon atoms, and an ether having 4 to 10 carbon atoms;

[0014] Preferably, the second solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0015] Optionally, the sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethyl)sulfonylimide, sodium trifluoromethylsulfonate, sodium tetrafluoroborate, and sodium perchlorate.

[0016] Optionally, the additive includes at least one of cyclic carbonate compounds, fluorinated cyclic carbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, phosphate compounds, borate compounds or nitrile compounds.

[0017] Optionally, the positive electrode active material includes at least one of a layered transition metal oxide and a polyphosphate compound;

[0018] Preferably, the chemical formula of the layered transition metal oxide is Na p Ni m Mn n M (1-m-n) O q , wherein 0<p≤1, 0≤m<1, 0<m+n<1, 1<q≤2, M is selected from at least one of Fe, Cu, Ti, and Co; more preferably, the layered transition metal oxide is selected from NaNi 0.3 Mn 0.3 Fe 0.4 O2、NaNi 0.4 Mn 0.4 Fe 0.2 O2 or NaNi 0.5 Mn 0.35 Fe 0.15 At least one of O2.

[0019] According to the sodium ion battery provided by the present invention, the potential of the nickel-containing sodium supplement agent participating in the reaction is relatively high. Within the limited voltage range, the nickel-containing sodium supplement agent reacts to release a large amount of active sodium, thereby increasing the battery's initial discharge capacity and thus improving the battery's initial coulombic efficiency. A fluoroether solvent is introduced into the electrolyte of the sodium ion battery. The fluoroether is not easily oxidized and can be preferentially solvated with sodium ions, reducing the oxidation probability and solvation degree of other solvents, thereby inhibiting the chain breaking and decomposition of other solvents in the electrolyte to produce gas, thereby improving the stability of the electrolyte and the cycle performance of the battery.

[0020] Through experiments, it was found that when the sodium supplement content, upper limit voltage, and fluoroether content satisfy the relationship 1.0≤A*B / C≤4.0, the sodium ion battery has better first efficiency and cycle capacity retention rate, and inhibits cycle gas production. When A*B / C<1.0, the sodium supplement content or upper limit voltage is low, the fluoroether solvent content is high, the sodium supplement effect is not good, the first efficiency of the sodium battery deteriorates, and the battery cycle impedance increases; when A*B / C>4.0, the sodium supplement content and the upper limit voltage are high, the fluoroether solvent content is low, the battery cycle deteriorates, and gas production is serious. By regulating the relationship between the solvent fluoroether content, the nickel-based sodium supplement content, and the upper limit voltage, the battery performance can be effectively improved. DETAILED DESCRIPTION

[0021] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0022] A sodium ion battery according to an embodiment of the present invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, a sodium supplement, a conductive agent and a binder, and the sodium supplement comprises Na x Ni y O z , wherein 1≤x≤2, 0≤y≤1, 1≤z≤2, and the mass percentage of the sodium supplement in the positive electrode material layer is A;

[0023] The upper voltage limit is BV;

[0024] The electrolyte includes a first solvent, a sodium salt and an additive, wherein the first solvent includes a fluoroether, and the mass percentage of the fluoroether in the electrolyte is C;

[0025] A, B, and C satisfy the relationship: 1.0≤A*B / C≤4.0.

[0026] In the sodium ion battery of the embodiment of the present invention, the nickel-containing sodium supplement used has a high potential for participating in the reaction. Within a limited voltage range, the nickel-containing sodium supplement reacts to release a large amount of active sodium, thereby increasing the battery's initial discharge capacity and improving the battery's initial coulombic efficiency. Fluorinated ether solvents are introduced into the electrolyte of the sodium ion battery. Fluorinated ethers are not easily oxidized and can preferentially solvate with sodium ions, reducing the oxidation probability and solvation degree of other solvents, thereby inhibiting the chain scission and decomposition of other solvents in the electrolyte to produce gas, improving the stability of the electrolyte and improving the cycle performance of the battery.

[0027] Through experiments, it was found that when the sodium supplement content, upper limit voltage, and fluoroether content satisfy the relationship 1.0≤A*B / C≤4.0, the sodium ion battery has better first efficiency and cycle capacity retention rate, and inhibits cycle gas production. When A*B / C<1.0, the sodium supplement content or upper limit voltage is low, the fluoroether solvent content is high, the sodium supplement effect is not good, the first efficiency of the sodium battery deteriorates, and the battery cycle impedance increases; when A*B / C>4.0, the sodium supplement content and the upper limit voltage are high, the fluoroether solvent content is low, the battery cycle deteriorates, and gas production is serious. By regulating the relationship between the solvent fluoroether content, the nickel-based sodium supplement content, and the upper limit voltage, the battery performance can be effectively improved.

[0028] In specific embodiments, A*B / C can be 1.0, 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0.

[0029] In some embodiments, A is 5%-10%.

[0030] In specific embodiments, A may be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0031] In the embodiment of the present invention, when the content of the nickel-containing sodium supplement is too low, the sodium ions of the sodium supplement are insufficient, the sodium supplement effect during the first charge and discharge process is poor, and the first efficiency of the battery is degraded; when the content of the nickel-containing sodium supplement is too high, the solvent decomposition side reaction is aggravated, resulting in battery cycle degradation and serious cycle gas production. By optimizing the mass percentage of the sodium supplement in the positive electrode material layer, the first efficiency and cycle performance of the sodium ion battery can be further improved, and gas production can be suppressed.

[0032] In some embodiments, B is 4.0-4.2.

[0033] In specific embodiments, B can be 4.0, 4.02, 4.05, 4.08, 4.1, 4.12, 4.15, 4.18, or 4.2.

[0034] In the embodiment of the present invention, the upper limit voltage range is preferably selected, and the upper limit voltage is the upper limit voltage of the battery charging, thereby further improving the first efficiency and cycle performance of the sodium ion battery and inhibiting gas production. When the voltage is too low, the nickel-based metal oxide participates in the reaction to a low degree, the sodium ion release of the sodium supplement is less, the sodium supplement effect is not good, and the battery first efficiency is low; when the voltage is too high, the solvent decomposition side reaction is aggravated, the battery cycle deteriorates, and the cycle gas production is serious.

[0035] In some embodiments, C is 10%-40%.

[0036] In specific embodiments, C may be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, or 40%.

[0037] In the embodiment of the present invention, the mass percentage of the fluoroether in the electrolyte is optimized, thereby further improving the first effect and cycle performance of the sodium ion battery and inhibiting gas production. When the fluoroether content is too low, the solvent decomposition cannot be inhibited, resulting in battery cycle degradation and severe cycle gas production; when the fluoroether content is too high, the first effect of the sodium battery is degraded and the battery cycle impedance increases.

[0038] In some embodiments, the sodium supplement includes NaNiO2, Na2NiO2, Na 1.9 Ni 0.7 O2、Na 1.6 Ni 0.8 O2、Na 1.3 Ni 0.9 O2、NaNi0.5 O、Na 1.2 Ni 0.4 O or Na 1.4 Ni 0.3 O, preferably, Na2NiO2, NaNiO2, NaNi 0.5 In the embodiment of the present invention, the type of nickel-based sodium supplement is preferably selected, thereby further improving the first efficiency and cycle performance of the sodium ion battery and inhibiting gas production.

[0039] In some embodiments, the fluorinated ether includes 1,2,3,3,4,4,5,5-octafluoropentyl methyl ether, 1,2,3,3,4,4,5,5-octafluoropentyl ethyl ether, 2,2,3,3,4,4,5-heptafluoropentyl methyl ether, 2,2,3,3,4,4,5-heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5-octafluoropentyl methyl ether, 2,2,3,3,4,4,5-heptafluoropentyl ethyl ether, ,4,5,5-octafluoropentyl ethyl ether, 1,2,2,3,3,4,4-heptafluorobutyl methyl ether, 2,2,3,3,4,4-hexafluorobutyl methyl ether, 2,2,3,3,4,4,5,5,6-nonafluorohexyl methyl ether, 2,2,3,3,4,4,5,5,6,6-decafluorohexyl methyl ether, 2,2,3,3,4,4,5,5-octafluorohexyl methyl ether. In the embodiment of the present invention, the type of fluorinated ether is preferred, thereby further improving the first efficiency and cycle performance of the sodium ion battery and inhibiting gas production.

[0040] In some embodiments, the electrolyte further comprises a second solvent; the second solvent comprises at least one of a non-fluorine-substituted carbonate having 3 to 7 carbon atoms, a carboxylic acid ester having 2 to 6 carbon atoms, and an ether having 4 to 10 carbon atoms;

[0041] Preferably, the non-fluorine-substituted carbonate having 3 to 7 carbon atoms includes at least one of cyclic or chain carbonates having 3 to 7 carbon atoms; the cyclic carbonate having 3 to 7 carbon atoms includes at least one of ethylene carbonate, vinylene carbonate, vinylethylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; the chain carbonate having 3 to 7 carbon atoms includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate;

[0042] Preferably, the carboxylic acid ester having 2 to 6 carbon atoms includes at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, and propyl propionate;

[0043] Preferably, the ether having 4 to 10 carbon atoms includes at least one of cyclic ethers or chain ethers having 4 to 10 carbon atoms; the cyclic ether having 4 to 10 carbon atoms includes at least one of 1,3-dioxolane, 1,4-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ether having 4 to 10 carbon atoms includes at least one of dimethoxymethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and diethylene glycol dimethyl ether;

[0044] More preferably, the second solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0045] In some embodiments, the sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethyl)sulfonyl imide, sodium bis(trifluoromethyl)sulfonyl imide, sodium trifluoromethylsulfonate, sodium tetrafluoroborate, and sodium perchlorate; the mass percentage of the sodium salt in the electrolyte is 5% to 15%, specifically, for example, 5%, 8%, 10%, 12%, 14%, and 15%.

[0046] In some embodiments, the additive includes at least one of cyclic carbonate compounds, fluorinated cyclic carbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, phosphate compounds, borate compounds or nitrile compounds, preferably vinylene carbonate, vinyl sulfate; the mass percentage of the additive in the electrolyte is 0.5% to 10%, specifically, for example, 0.5%, 1%, 2%, 5%, 10%. In the embodiment of the present invention, the performance of the sodium ion battery is further improved by preferably adding the additive.

[0047] In some embodiments, the positive electrode active material includes at least one of a layered transition metal oxide and a polyphosphate compound;

[0048] Preferably, the chemical formula of the layered transition metal oxide is Na p Ni m Mn n M (1-m-n) O q , wherein 0<p≤1, 0≤m<1, 0<m+n<1, 1<q≤2, M is selected from at least one of Fe, Cu, Ti, and Co; more preferably, the layered transition metal oxide is selected from NaNi 0.3 Mn 0.3 Fe 0.4 O2、NaNi 0.4 Mn 0.4Fe 0.2 O2 or NaNi 0.5 Mn 0.35 Fe 0.15 At least one of O2.

[0049] In some embodiments, the negative electrode includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based material, a silicon-based material, and a tin-based material; and the carbon-based material is hard carbon.

[0050] In some embodiments, the preparation method of the positive electrode includes: mixing the positive electrode active material, sodium supplement, binder, conductive agent, and solvent, coating on a substrate, removing the solvent, and obtaining a positive electrode, and optionally, the substrate is a current collector; the preparation method of the negative electrode includes: mixing the negative electrode active material, binder, conductive agent, and solvent, coating on a substrate, and removing the solvent to obtain a negative electrode. In the embodiments of the present invention, there is no particular limitation on the conductive agent, binder, and solvent, and the conductive agent, binder, and solvent can all be conductive agents, binders, and solvents commonly used in the art.

[0051] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0052] Embodiment 1:

[0053] Sodium-ion batteries include:

[0054] (1) Electrolyte: The second solvent, the first solvent, the sodium salt, and the additive are prepared into a solution in a mass ratio of 62:20:14:4; the first solvent is a fluoroether, the fluoroether is 2,2,3,3,4,4,5,5,6-nonafluorohexyl methyl ether, the second solvent is ethyl methyl carbonate, the sodium salt is NaPF6, and the additive is vinylene carbonate and vinyl sulfate in a mass ratio of 1:1, and the mass percentage of the fluoroether in the electrolyte is 20%.

[0055] (2) Positive electrode: The positive electrode material layer is composed of positive electrode active material, sodium supplement, conductive agent and binder in a mass ratio of 88:7:2:3; the positive electrode active material is NaNi 0.3 Mn 0.3 Fe 0.4 O2, the sodium supplement is NaNiO2, and the mass percentage of the sodium supplement in the positive electrode material layer is 7%.

[0056] The positive electrode active material, sodium supplement, conductive carbon black Super-P and binder polyvinylidene fluoride are mixed and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain positive electrode slurry. Aluminum foil is used as the positive electrode current collector, and the slurry is evenly coated on both sides of the aluminum foil. After drying, rolling and vacuum drying, the positive electrode material layer is obtained, and the aluminum lead wire is welded with an ultrasonic welder to obtain the positive electrode plate.

[0057] (3) Sodium ion battery: The electrolyte, positive electrode, hard carbon negative electrode and PP separator are combined into a battery.

[0058] Example 2-18

[0059] Examples 2-18 are used to illustrate the sodium ion battery disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0060] The type and mass percentage of the sodium supplement used in Examples 2-18, the upper limit voltage, and the type and mass percentage of the fluoroether are shown in Table 1.

[0061] Comparative Examples 1-8

[0062] Comparative Examples 1-8 are used to compare and illustrate the sodium ion battery disclosed in the present invention, including most of the operating steps in Example 1, except that:

[0063] The types and mass percentages of the sodium supplementing agents, the upper limit voltages, and the types and mass percentages of the fluoroethers used in Comparative Examples 1-8 are shown in Table 1.

[0064] Performance Testing

[0065] The above-mentioned sodium ion battery was subjected to the following performance tests:

[0066] (1) Initial efficiency test: The battery was placed at 45°C for 2 h, charged at a constant current rate of 0.2C to the upper limit voltage, then charged at a constant voltage rate to a current of 0.03C, and the charging capacity C1 was recorded; the battery was discharged at a constant current rate of 0.2C to 1.5V, and the discharge capacity C2 was recorded.

[0067] First efficiency (%) = discharge capacity C2 / charge capacity C1×100%.

[0068] (2) Cyclic capacity retention and gas generation test: The formed battery was placed at 45°C for 2 h, and the battery volume V1 was tested; the battery was charged at a constant current of 0.5C to the upper limit voltage, and then charged at a constant voltage to a current of 0.03C, and then discharged at a constant current of 1C to 1.5V, and the discharge capacity D1 was recorded; the battery was charged and discharged 200 times, and the discharge capacity D2 of the 200th discharge was recorded; and the battery volume V2 was tested.

[0069] Capacity retention rate after 200 cycles (%) = D2 / D1×100%.

[0070] Cycle gas production rate (%) = (V2-V1) / V1×100%.

[0071] Table 1

[0072]

[0073] The performance test results of the sodium ion batteries of Examples 1-18 and Comparative Examples 1-8 are shown in Table 2.

[0074] Table 2

[0075] serial number First effect (%) Cycle capacity retention rate (%) Cycle gas production rate (%) Example 1 89.1％ 93.1％ 17.4％ Example 2 87.5％ 91.6％ 11.6％ Example 3 88.9％ 90.6％ 17.5％ Example 4 87.2％ 93.3％ 22.0％ Example 5 87.9％ 92.5％ 34.1％ Example 6 82.4％ 92.9％ 11.9％ Example 7 89.9％ 90.1％ 25.1％ Example 8 85.3％ 87.3％ 37.2％ Example 9 84.7％ 92.1％ 27.1％ Example 10 88.4％ 86.2％ 38.2％ Embodiment 11 85.0％ 91.1％ 12.0％ Example 12 88.4％ 94.2％ 29.6％ Embodiment 13 89.6％ 90.8％ 32.9％ Embodiment 14 89.9％ 90.5％ 10.8％ Embodiment 15 88.3％ 90.2％ 27.9％ Example 16 89.1％ 93.9％ 20.9％ Embodiment 17 89.2％ 95.0％ 31.3％ Embodiment 18 88.9％ 79.1％ 53.0％ Comparative Example 1 73.9％ 84.7％ 60.1％ Comparative Example 2 76.5％ 77.1％ 70.9％ Comparative Example 3 73.8％ 81.4％ 68.4％ Comparative Example 4 80.0％ 83.4％ 54.8％ Comparative Example 5 77.9％ 77.9％ 64.2％ Comparative Example 6 72.1％ 83.4％ 63.7％ Comparative Example 7 74.7％ 80.9％ 51.1％ Comparative Example 8 73.8％ 84.2％ 54.2％

[0076] It can be seen from Tables 1 and 2 that the sodium ion batteries prepared in Examples 1-18, the content of the nickel-containing sodium supplement, the upper limit voltage, and the fluoroether content satisfy the relationship 1.0≤A*B / C≤4.0, which can simultaneously improve the first efficiency, cycle capacity retention rate, and cycle gas production rate of the sodium ion battery.

[0077] It can be seen from the test results of Examples 1-5 and 6-11 that when the relationship: 1.0≤A*B / C≤4.0 is satisfied, and the preferred conditions 5%≤A≤10%, 4.0≤B≤4.2 and 10%≤C≤40% are satisfied, the first efficiency, cycle and gas production performance of the sodium ion battery can be further improved.

[0078] It can be seen from the test results of Comparative Examples 1-6 that when 1.0≤A*B / C≤4.0 is not satisfied, the first effect and cycle performance of the sodium ion battery are poor, and the cycle gas production rate is high. In Comparative Example 1, the sodium supplement content and the upper limit voltage are low, the fluoroether solvent content is high, A*B / C is 0.8, the battery cycle performance is deteriorated, the cycle gas production rate is 60.1%, and the cycle gas production is serious. In Comparative Example 2, the sodium supplement content and the upper limit voltage are high, the fluoroether solvent content is low, A*B / C is 4.2, the battery cycle performance is deteriorated, the cycle capacity retention rate is 77.1%, and the cycle gas production rate is 70.9%. In Comparative Example 6, the sodium supplement content is high, the upper limit voltage is high, the solvent decomposition side reaction is aggravated, and the fluorosolvent content of the electrolyte is low, and the solvent decomposition cannot be suppressed, resulting in battery cycle degradation and serious cycle gas production.

[0079] It can be seen from the test results of Examples 1 and 12-14 that for different nickel-based sodium supplements in the present invention, when the relationship 1.0≤A*B / C≤4.0 is satisfied, the effects they play are similar, and the obtained sodium ion battery has a higher first efficiency, excellent cycle capacity retention rate and lower cycle gas production rate.

[0080] It can be seen from the test results of Examples 1, 12-14 and Comparative Examples 7-8 that when other sodium supplements are used to replace the sodium supplement in the present invention, the performance improvement of the sodium ion battery is not as good as that of the sodium supplement in the present invention under the same other conditions.

[0081] From the test results of Examples 1, 15-17, it can be seen that for different fluoroethers in the present invention, when the relationship 1.0≤A*B / C≤4.0 is satisfied, the first efficiency and cycle performance of the sodium ion battery can be improved and gas production can be suppressed. In Example 18, 2-monofluoropentyl ethyl ether was used, and the battery cycle performance was relatively poor, with a cycle capacity retention rate of 79.1% and a cycle gas production rate of 53.0%.

[0082] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0083] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within 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 an electrolyte, wherein the positive electrode comprises a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material, a sodium supplement, a conductive agent and a binder, wherein the sodium supplement comprises Na x Ni y O z , wherein 1≤x≤2, 0≤y≤1, 1≤z≤2, and the mass percentage of the sodium supplement in the positive electrode material layer is A; The upper voltage limit is BV; The electrolyte comprises a first solvent, a sodium salt and an additive, wherein the first solvent comprises a fluoroether, and the mass percentage of the fluoroether in the electrolyte is C; A, B, and C satisfy the relationship: 1.0≤A*B / C≤4.

0.

2. The sodium ion battery according to claim 1, characterized in that A is 5%-10%.

3. The sodium ion battery according to claim 1, characterized in that: B is 4.0-4.

2.

4. The sodium ion battery according to claim 1, characterized in that C is 10%-40%.

5. The sodium ion battery according to claim 1, characterized in that: The sodium supplement includes NaNiO2, Na2NiO2, Na 1.9 Ni 0.7 O2、Na 1.6 Ni 0.8 O2、Na 1.3 Ni 0.9 O2、NaNi 0.5 O、Na 1.2 Ni 0.4 O or Na 1.4 Ni 0.3 At least one of O.

6. The sodium ion battery according to claim 1, characterized in that: The fluoroethers include 1,2,3,3,4,4,5,5-octafluoropentyl methyl ether, 1,2,3,3,4,4,5,5-octafluoropentyl ethyl ether, 2,2,3,3,4,4,5-heptafluoropentyl methyl ether, 2,2,3,3,4,4,5-heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5-octafluoropentyl methyl ether, 2,2,3,3,4,4,5 , at least one of 1,5-octafluoropentyl ethyl ether, 1,2,2,3,3,4,4-heptafluorobutyl methyl ether, 2,2,3,3,4,4-hexafluorobutyl methyl ether, 2,2,3,3,4,4,5,5,6-nonafluorohexyl methyl ether, 2,2,3,3,4,4,5,5,6,6-decafluorohexyl methyl ether, and 2,2,3,3,4,4,5,5-octafluorohexyl methyl ether.

7. The sodium ion battery according to claim 1, characterized in that: The electrolyte further includes a second solvent; the second solvent includes at least one of a non-fluorine-substituted carbonate having 3 to 7 carbon atoms, a carboxylic acid ester having 2 to 6 carbon atoms, and an ether having 4 to 10 carbon atoms; Preferably, the second solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

8. The sodium ion battery according to claim 1, characterized in that: The sodium salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethyl)sulfonyl imide, sodium trifluoromethylsulfonate, sodium tetrafluoroborate and sodium perchlorate.

9. The sodium ion battery according to claim 1, characterized in that: The additive includes at least one of cyclic carbonate compounds, fluorinated cyclic carbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, phosphate compounds, borate compounds or nitrile compounds.

10. 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 and a polyphosphate compound; Preferably, the chemical formula of the layered transition metal oxide is Na p Ni m Mn n M (1-m-n) O q , wherein 0<p≤1, 0≤m<1, 0<m+n<1, 1<q≤2, M is selected from at least one of Fe, Cu, Ti, and Co; more preferably, the layered transition metal oxide is selected from NaNi 0.3 Mn 0.3 Fe 0.4 O2、NaNi 0.4 Mn 0.4 Fe 0.2 O2 or NaNi 0.5 Mn 0.35 Fe 0.15 At least one of O2.

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