Formation method of sodium-ion battery and sodium-ion battery

Abstract

The application relates to the technical field of batteries, in particular to a formation method of a sodium ion battery and the sodium ion battery. The formation method of the sodium ion battery comprises the following steps: performing a constant-current charge-discharge cycle on a sodium ion battery to be formed according to first charge-discharge conditions, and completing a first formation stage; performing a constant-current charge-discharge cycle on the sodium ion battery completing the first formation stage according to second charge-discharge conditions, and completing a second formation stage; wherein the voltage in the first charge-discharge conditions is less than the voltage in the second charge-discharge conditions. The application can achieve in-situ self-repairing sodium supplement and high-stability SEI construction, improve the high-temperature stability of the SEI film of the sodium ion battery, and further improve the cycle performance of the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a formation method of a sodium ion battery and the sodium ion battery. BACKGROUND

[0002] Sodium has similar physical and chemical properties to lithium, that is, the working principle of the sodium ion battery is similar to that of the lithium ion battery. Compared with the lithium ion battery, the sodium ion battery has good low-temperature performance, high safety, low cost, rich resources and long-term large-scale storage, and has a wide application prospect in the energy storage field, and is expected to replace the lithium ion battery in the energy storage field and be widely used. However, in the sodium ion battery, due to the low Lewis acidity of the sodium complex, the generated solid electrolyte interface film (SEI film) is unstable, especially at high temperature, which will dissolve in the carbonate solvent, the SEI film will be destroyed, the electrolyte will directly contact the negative electrode interface, and a negative reaction will occur, generating a large amount of gas, thereby causing the performance of the battery to deteriorate and the active sodium to be rapidly consumed.

[0003] In order to alleviate the above problems, a sodium ion battery electrolyte is proposed in the related art, by adding lithium salt additives to the electrolyte, using the inorganic compound of lithium reduced on the surface of the negative electrode in the lithium salt formation process to form a stable and firm inorganic SEI layer on the surface of the negative electrode, to solve the problem of SEI high-temperature dissolution, and to improve the high-temperature performance and cycle performance of the sodium ion battery. However, the above method still has certain deficiencies, on the one hand, when the electrolyte adds a large amount of lithium salt additives, a relatively dense lithium inorganic compound SEI film is generated, which will inevitably affect the transmission of sodium ions, increase the interface impedance of the battery, and adversely affect the charge and discharge performance of the battery; on the other hand, due to the high sodium potential, lithium ions will also be inserted into the negative electrode at the same time as the formation of the lithium salt, thereby hindering the insertion of sodium ions into the negative electrode during the formation stage, and affecting the activation and overall performance of the negative electrode material. In addition, the lithium salt additives added in the electrolyte have high cost, which conflicts with the positioning of the sodium ion battery market, and the addition of lithium salt does not directly supplement the sodium source.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] In view of this, the present application aims to at least solve one of the technical problems in the related art to some extent. To this end, the present application provides a formation method of a sodium ion battery and the sodium ion battery, which can alleviate the problem of unstable SEI film in the sodium ion battery, improve the stability of the SEI film, and thus improve the cycle performance of the sodium ion battery.

[0006] In order to solve the above technical problems, the present application is implemented as follows:

[0007] According to one aspect of the present application, the embodiments of the present application provide a formation method of a sodium ion battery, the sodium ion battery comprising a positive plate, the positive plate comprising a sodium ion positive material and a lithium ion positive material, the lithium ion positive material comprising lithium iron phosphate and / or lithium manganese iron phosphate;

[0008] The formation method comprises the following steps:

[0009] performing a constant current charge-discharge cycle on the sodium ion battery to be formed according to a first charge-discharge condition, to complete a first formation stage;

[0010] performing a constant current charge-discharge cycle on the sodium ion battery completing the first formation stage according to a second charge-discharge condition, to complete a second formation stage;

[0011] In the first charge-discharge condition, the voltage is ≤ the voltage in the second charge-discharge condition.

[0012] In addition, the formation method of the sodium ion battery according to the present application can also have the following additional technical features:

[0013] In some embodiments, in the first charge-discharge condition, the voltage ranges from 1.5V to 3V, preferably from 2V to 3V.

[0014] In some embodiments, in the second charge-discharge condition, the voltage ranges from 3V to 3.4V.

[0015] In some embodiments, in the first charge-discharge condition, the lower limit voltage is V1 and the upper limit voltage is V2, the V1 satisfies: 1.5V≤V1≤2V, and the V2 satisfies: 2.9V≤V2<3V. Preferably, the V1 is 2V.

[0016] In some embodiments, in the second charge-discharge condition, the lower limit voltage is V3 and the upper limit voltage is V4, the V3 satisfies: 3V≤V3<3.3V, and the V4 satisfies: 3.3V≤V4<3.4V. Preferably, the V3 is 3V,

[0017] In some embodiments, in the first charge-discharge condition, the charging current and the discharging current are both I1, and the I1 satisfies: 0.1C<I1≤0.3C.

[0018] In some embodiments, in the second charge-discharge condition, the charging current and the discharging current are both I2, and the I2 satisfies: I2≤0.1C.

[0019] In some embodiments, in the first charge-discharge condition, the number of cycles is c1, and the c1 satisfies: 2≤c1≤4.

[0020] In some embodiments, the number of cycles c2 in the second charge-discharge condition satisfies: 4≤c2≤6.

[0021] In some embodiments, the ambient temperature T1 in the first charge-discharge condition satisfies: T1≤45℃.

[0022] In some embodiments, the ambient temperature T2 in the second charge-discharge condition satisfies: T2≥60℃.

[0023] In some embodiments, the first formation stage specifically comprises:

[0024] S10, placing the sodium-ion battery to be formed at a temperature T1 for a first time;

[0025] S20, charging the sodium-ion battery after the first time at a current I1 to a voltage V2 at the temperature T1, and then placing the sodium-ion battery for a second time;

[0026] S30, discharging the sodium-ion battery after the second time at the current I1 to a voltage V1 at the temperature T1, and then placing the sodium-ion battery for a third time;

[0027] The above steps S10 to S30 are repeated for c1 times to complete the first formation stage.

[0028] In some embodiments, the second formation stage specifically comprises:

[0029] S40, placing the sodium-ion battery after the first formation stage at a temperature T2 for a fourth time;

[0030] S50, charging the sodium-ion battery after the fourth time at a current I2 to a voltage V4 at the temperature T2, and then placing the sodium-ion battery for a fifth time;

[0031] S60, discharging the sodium-ion battery after the fifth time at the current I2 to a voltage V3 at the temperature T2, and then placing the sodium-ion battery for a sixth time;

[0032] The above steps S40 to S60 are repeated for c2 times to complete the second formation stage.

[0033] According to another aspect of the present application, the embodiments of the present application provide a sodium-ion battery, which is prepared by the formation method of the sodium-ion battery as described above.

[0034] In some embodiments, the positive electrode sheet in the sodium-ion battery comprises a current collector and a positive electrode active material layer disposed on the surface of the current collector, the positive electrode active material layer comprises a sodium-ion positive electrode material and a lithium-ion positive electrode material, and the mass ratio of the lithium-ion positive electrode material in the positive electrode active material layer is 0.3% to 5%.

[0035] In some embodiments, the positive electrode active material layer further comprises a conductive agent and a binder, and the mass ratio of the sodium-ion positive electrode material, the conductive agent and the binder is (85 to 99):(0.5 to 5):(0.5 to 5).

[0036] In some embodiments, the sodium-ion positive electrode material comprises a layered oxide sodium-ion positive electrode material.

[0037] In some embodiments, the chemical formula of the layered oxide sodium-ion positive electrode material is Na x TMO2, wherein TM represents at least one element selected from Ti, Ni, Mn, Fe, V, Cr, Co, Cu, Zn or Li, and x is greater than or equal to 1 / 3.

[0038] The technical solutions of the present application have at least the following advantages:

[0039] In the embodiments of the present application, the formation method of the sodium-ion battery can be used for the formation of the sodium-ion battery, the positive electrode sheet of which comprises a sodium-ion positive electrode material and a lithium-ion positive electrode material, the lithium-ion positive electrode material comprises lithium iron phosphate and / or lithium manganese iron phosphate, and the formation comprises two stages, the voltage of the first formation stage is less than or equal to the voltage of the second formation stage. Thus, by adding the lithium-ion positive electrode material in the positive electrode sheet of the sodium-ion battery, since the delithiation potential of the lithium-ion positive electrode material such as lithium iron phosphate and / or lithium manganese iron phosphate is higher than that of the sodium-ion positive electrode material, the lithium-ion positive electrode material will release lithium ions after the sodium-ion positive electrode material is partially desodiated, so that by setting two formation stages and making the formation voltage of the first formation stage less than or equal to the formation voltage of the second formation stage, only sodium ions are released on the positive electrode side in the first formation stage, and less lithium ions are released, and sodium ions participate in film formation and negative electrode sodium intercalation activation at the same time, so that an unstable SEI film is pre-constructed in the first formation stage and the negative electrode is activated; further, in the second formation stage, the voltage is relatively high, and in this stage, lithium ions are mainly released on the positive electrode side, so as to provide a lithium source in situ in the sodium battery system, and the original unstable SEI is self-repaired, so as to form a high-stability SEI layer, and the negative electrode sodium intercalation activation is not affected; at the same time, the sodium ions dissolved from the SEI will intercalate into the negative electrode with electrons released from the positive electrode of the lithium-ion positive electrode material, so as to achieve in-situ self-repairing and high-stability SEI construction. Thus, the stability of the SEI film of the sodium-ion battery is improved, which is beneficial to improving the cycle performance of the sodium-ion battery.

[0040] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and / or can be learned by practice of the application. DETAILED DESCRIPTION

[0041] The application will be further described with reference to the following examples. It should be understood that these examples are intended to illustrate the application and are not intended to limit the scope of the application.

[0042] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be approximations which are also meant to cover or range customarily known equivalents or approximations thereof. For numerical ranges expressed in the format "from x to y," "x to y," or "x-y," it is meant that every number or value within the range is also specifically enumerated. For example, "from 1 to 10" or "1 to 10" means each number from 1 to 10, i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10, is specifically enumerated. For ranges expressed in fractions, percentages, or decimals, every value or point within the range is also specifically enumerated. For example, "from 30% to 70%," or "30-70%," means 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, and 70% are specifically enumerated.

[0043] If not specifically stated, all steps of the application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0044] If not specifically stated, the "comprise" and "include" mentioned in the application means open, and can also be closed. For example, the "comprise" and "include" can mean that other components not listed can also be included, or only the listed components can be included.

[0045] Research on sodium-ion batteries has rapidly developed in recent years. However, as analyzed in the background art, there are still some deficiencies in the current sodium-ion batteries and the preparation thereof, especially, due to the low Lewis acidity of sodium complex in sodium-ion batteries, the generated SEI film is unstable, especially the SEI film is more unstable at high temperature, which will affect the electrochemical performance of the battery.

[0046] In view of this, the inventors of the present application start from the perspective of improving the stability of the SEI film of the sodium-ion battery and further improving the cycle performance of the battery, and through in-depth research, find and propose that the existing formation method of the sodium-ion battery is improved, so as to provide a scheme of in-situ self-repairing sodium supplement and high-stability SEI design for the sodium-ion battery, so as to improve the stability of the SEI film, especially the stability of the SEI film at high temperature, and further improve the cycle life of the battery. Next, the present application will be described in detail.

[0047] In some embodiments, a formation method of a sodium-ion battery is provided, which is suitable for application in a sodium-ion battery including a positive electrode sheet including a sodium-ion positive electrode material and a lithium-ion positive electrode material, that is, the positive electrode sheet contains both the sodium-ion positive electrode material and the lithium-ion positive electrode material, and the lithium-ion positive electrode material includes lithium iron phosphate and / or lithium manganese iron phosphate; for example, the lithium-ion positive electrode material can use lithium iron phosphate, or can use lithium manganese iron phosphate, or can use a combination of lithium iron phosphate and lithium manganese iron phosphate.

[0048] Optionally, in the above-mentioned positive electrode sheet, the content of the sodium-ion positive electrode material is greater than the content of the lithium-ion positive electrode material, that is, in the positive electrode sheet, the sodium-ion positive electrode material is the main positive electrode active material, and the lithium-ion positive electrode material is a doped positive electrode material.

[0049] In the present application, the provided formation method of a sodium-ion battery includes the following steps:

[0050] According to the first charge and discharge condition, the sodium-ion battery to be formed is subjected to constant-current charge and discharge cycles to complete the first formation stage;

[0051] According to the second charge and discharge condition, the sodium-ion battery completing the first formation stage is subjected to constant-current charge and discharge cycles to complete the second formation stage;

[0052] Among them, the voltage in the first charge and discharge condition is less than the voltage in the second charge and discharge condition.

[0053] The above formation can be divided into two stages, for example, in the first formation stage, under the first charge and discharge condition, the sodium-ion battery to be formed is subjected to constant-current charging and constant-current discharging, and after a suitable number of cycles, the first formation stage can be completed. In the second formation stage, under the second charge and discharge condition, the sodium-ion battery completing the first formation stage is subjected to constant-current charging and constant-current discharging, and after a suitable number of cycles, the second formation stage can be completed. The first charge and discharge condition and the second charge and discharge condition can include current, voltage, temperature, cycle number, etc.

[0054] The voltage range in the first charge-discharge condition (i.e., the voltage range in the first formation stage) needs to be less than or equal to the voltage range in the second charge-discharge condition (i.e., the voltage range in the second formation stage). Thus, different positive electrode materials can be used to release lithium or sodium in different voltage ranges.

[0055] Generally, for different positive electrode active materials, the reaction potential of sodium / lithium intercalation and deintercalation is specific, thus determining the working voltage range of each material. The formation method described in the present application is based on the electrochemical characteristics of the sodium ion battery system itself, mainly aiming at the instability of the conventional SEI film of the sodium ion battery negative electrode. A small amount of lithium ion positive electrode material is doped in the positive electrode sheet of the sodium ion battery, and a specific formation design is used, such as using the different voltage ranges of sodium deintercalation and lithium deintercalation of sodium ion positive electrode materials and lithium ion positive electrode materials, dividing the formation into two stages, and making the voltage ranges of the two stages different to perform in-situ self-repairing and sodium supplementing and construction of a high-stability SEI film on the negative electrode side. In detail:

[0056] In the embodiments of the present application, based on the problem of high solubility of sodium complex of sodium SEI, a small amount of lithium ion positive electrode material such as lithium iron phosphate and / or lithium manganese iron phosphate is doped in the positive electrode sheet of the sodium ion battery. Since the deintercalation potential of the lithium ion positive electrode material such as lithium iron phosphate and / or lithium manganese iron phosphate is higher than that of the sodium ion positive electrode material, the lithium ion positive electrode material will release lithium ions after the sodium ion positive electrode material is partially deintercalated. Therefore, by setting two formation stages and the formation voltage of the two stages, the formation voltage of the first formation stage is less than or equal to the formation voltage of the second formation stage, such as the formation voltage range of the first formation stage being 2V-3V and the formation voltage range of the second formation stage being 3V-3.4V. In this way, only sodium ions are released on the positive electrode side in the first formation stage, and less lithium ions are released. Sodium ions participate in the formation of the negative electrode and the activation of the negative electrode, thereby pre-constructing an unstable SEI film and activating the negative electrode in the first formation stage. Further, in the second formation stage, the voltage is relatively high. In this stage, lithium ions are mainly released on the positive electrode side, thereby providing lithium source in-situ in the sodium battery system and self-repairing the original unstable SEI, thereby forming a high-stability SEI layer without affecting the activation of the negative electrode. At the same time, the sodium ions dissolved from the SEI will be embedded into the negative electrode with the electrons released from the lithium ion positive electrode material positive electrode, thereby achieving in-situ self-repairing and sodium supplementing and high-stability SEI film construction. Thus, the stability of the SEI film of the sodium ion battery is improved, which is beneficial to improving the cycle performance of the sodium ion battery.

[0057] Compared with the prior art of adding lithium salt additives in the electrolyte, the method of the present application does not directly add lithium salt in the electrolyte, so it does not affect the initial activation process of the sodium negative electrode. The present application can make the pre-formation not de-lithiated, only de-sodium, so as to activate the initial sodium negative electrode. The later stage of the positive electrode is de-lithiated in large quantities and de-sodium in small quantities. The lithium ions released will repair the unstable SEI layer formed by the high-temperature dissolution of sodium complexes on the negative side. At the same time, the sodium ions dissolved from the SEI film will be embedded into the negative electrode with the electrons released from the lithium iron phosphate positive electrode, completing the in-situ sodium repair and constructing a high-stability SEI film for the sodium ion battery system.

[0058] In the present application, the lithium ion positive electrode material is one or both of lithium iron phosphate or lithium manganese iron phosphate. Preferably, the lithium ion positive electrode material is selected from lithium iron phosphate. This is because both lithium iron phosphate and lithium manganese iron phosphate have two stable de-lithiation platforms, which are more conducive to the pre-stage stable SEI construction and sodium repair mechanism of the present application. Other lithium ion positive electrode materials, such as ternary materials, release lithium ions stably throughout the voltage range, which is not conducive to the pre-stage stable SEI construction and sodium repair mechanism of the present application. In addition, the lithium iron phosphate positive electrode material belongs to the olivine structure, which has very excellent stability and is conducive to improving the cycle performance of the sodium ion battery.

[0059] In the present application, the sodium ion positive electrode material can be a layered sodium ion positive electrode material. The working voltage of the layered sodium ion positive electrode material and the lithium iron phosphate or lithium manganese iron phosphate positive electrode material satisfies a certain relationship. It should be noted that the voltage in the first charging and discharging condition needs to be less than or equal to the voltage in the second charging and discharging condition. The specific range of the voltage in the first charging and discharging condition and the specific range of the voltage in the second charging and discharging condition can be adjusted adaptively according to the specific types of the specific sodium ion positive electrode material and the specific lithium ion positive electrode material. That is, the specific range of the voltage in the first charging and discharging condition and the specific range of the voltage in the second charging and discharging condition can be different according to the specific types of the specific sodium ion positive electrode material and the specific lithium ion positive electrode material.

[0060] In some embodiments, in the first charging and discharging condition of the first formation stage, the voltage range is 1.5V-3V, preferably, under normal conditions, the voltage range is 2V-3V.

[0061] In some embodiments, in the second charging and discharging condition of the second formation stage, the voltage range is 3V-3.4V, and further, the voltage range is 3V-3.3V.

[0062] In the embodiments of the present application, the formation voltage of the first formation stage is preferably 2V-3V. In this stage, only sodium ions are released on the positive electrode side, and less lithium ions are released. Moreover, sodium ions participate in film formation and negative electrode sodium intercalation activation at the same time, thereby pre-building unstable SEI film and activating the negative electrode; the formation voltage of the second formation stage is 3V-3.4V, or 3V-3.3V. In this stage, mainly lithium ions are released on the positive electrode side, thereby providing lithium source in situ in the sodium battery system, and self-repairing the original unstable SEI, thereby forming a high-stable SEI layer, and without affecting the negative electrode sodium intercalation activation. At the same time, the sodium ions dissolved from the SEI will intercalate into the negative electrode in combination with the electrons released from the lithium iron phosphate positive electrode, thereby achieving in-situ self-repairing sodium supplement and high-stable SEI construction.

[0063] Specifically, in some embodiments, the provided formation method includes a first formation stage and a second formation stage, wherein the first formation stage specifically includes:

[0064] S10, placing the sodium ion battery to be formed at a T1 temperature for a first time;

[0065] S20, after the first time, charging the sodium ion battery at a T1 temperature with a current I1 to a voltage V2, and then placing it for a second time;

[0066] S30, after the second time, discharging the sodium ion battery at a T1 temperature with a current I1 to a voltage V1, and then placing it for a third time;

[0067] The above steps S10-S30 are cycled c1 times to complete the first formation stage.

[0068] In some embodiments, the second formation stage specifically includes:

[0069] S40, placing the sodium ion battery after completing the first formation stage at a T2 temperature for a fourth time;

[0070] S50, after the fourth time, charging the sodium ion battery at a T2 temperature with a current I2 to a voltage V4, and then placing it for a fifth time;

[0071] S60, after the fifth time, discharging the sodium ion battery at a T2 temperature with a current I2 to a voltage V3, and then placing it for a sixth time;

[0072] The above steps S40-S60 are cycled c2 times to complete the second formation stage.

[0073] Optionally, the time range of the first, second, third, fourth and fifth static time in the first and second formation stages can be 1 min to 10 min; further 3 min to 5 min. For example, the static time can be 1 min, 3 min, 5 min, 8 min, 10 min, etc., and of course can also be other values within the above range, which is not limited here. Preferably, the time of the above several static times can be 5 min.

[0074] In some embodiments, in the first formation stage, i.e. in the first charge and discharge condition, the voltage in step S30 is the lower limit voltage, which is V1, and the voltage in step S20 is the upper limit voltage, which is V2; wherein V1 satisfies: 1.5V≤V1≤2V, preferably, the value of V1 is 2V, or in some cases, the value of V1 can also be 1.5V; V2 satisfies: 2.9V≤V2<3V.

[0075] It should be understood that V1 is the lower limit of the discharge voltage of the sodium battery system, and generally V1 is 2V, or in some special cases, V1 can also be 1.5V according to different material type systems.

[0076] In some embodiments, in the second formation stage, i.e. in the second charge and discharge condition, the voltage in step S60 is the lower limit voltage, which is V3, and the voltage in step S50 is the upper limit voltage, which is V4; wherein V3 satisfies: 3V≤V3<3.3V, the value of V3 is set according to the lithium ion cathode material lithium iron phosphate or lithium manganese iron phosphate used, preferably, the value of V3 is 3V, and V4 satisfies: 3.3V≤V4<3.4V.

[0077] Therefore, by controlling the upper limit voltage and the lower limit voltage of the first and second formation stages within the above range, it is helpful to make the pre-formation stage (the first formation stage) not to be lithiumized, but only to be sodiumized, so as to activate the initial sodium battery negative electrode; the post-formation stage (the second formation stage) is largely lithiumized and a small amount of sodiumized, and the lithium ions released will repair the SEI layer unstable due to the high temperature dissolution of sodium complex on the negative electrode side, and the sodium ions dissolved from the SEI will be embedded into the negative electrode with the electrons released from the lithium iron phosphate cathode, completing the in-situ sodium supplement, so as to achieve the in-situ self-repairing and sodium supplement of the sodium ion battery system and the construction of the high-stability SEI film.

[0078] In the present application, on the basis of meeting the above voltage conditions, the current size of the first and second formation stages is further limited.

[0079] In some embodiments, in the first formation stage, i.e. in the first charge-discharge condition, the current of the constant current charge-discharge in steps S20 and S30 is I1, which satisfies: 0.1C < I1≤ 0.3C. For example, I1 can be 0.1C, 0.2C, 0.3C, etc., and of course can also be other values within the above range. Preferably, I1 is 0.2C.

[0080] In some embodiments, in the second formation stage, i.e. in the second charge-discharge condition, the current of the constant current charge-discharge in steps S50 and S60 is I2, which satisfies: I2≤ 0.1C. For example, I2 can be 0.1C, 0.08C, 0.06C, 0.05C, 0.03C, 0.01C, etc., and of course can also be less than 0.01C or other values within the range. Preferably, I2 is 0.05C.

[0081] In the present application, the current I1 of the first formation stage is preferably greater than the current I2 of the second formation stage.

[0082] By making the currents of the first formation stage and the second formation stage within the above range, it is helpful to make the sodium ion battery system better generate a dense and stable SEI film, which is beneficial to improve the cycle stability of the sodium ion battery. If the current of the first formation stage is less than the current of the second formation stage, the initial sodium ion is completely released, the pre-formed SEI film consumes too much, which will affect the initial capacity. If the current of the first formation stage is greater than 0.3C, due to polarization, the sodium ion is released less, the negative electrode is not fully activated, which will affect the long-term cycle performance of the sodium ion battery. If the current of the second formation stage is greater than 0.1C, the lithium ion cannot repair the SEI in time, which will cause the SEI to be not stable enough, which will affect the later cycle performance of the sodium ion battery.

[0083] In the present application, on the basis of satisfying the above voltage condition, the cycle number of the first formation stage and the second formation stage is further limited.

[0084] In some embodiments, in the first formation stage, i.e. in the first charge-discharge condition, the cycle number is c1, which satisfies: 2≤ c1≤ 4. For example, the cycle number c1 of the first formation stage can be 2, 3 or 4.

[0085] In some embodiments, in the second formation stage, i.e. in the second charge-discharge condition, the cycle number is c2, which satisfies: 4≤ c2≤ 6. For example, the cycle number c2 of the second formation stage can be 4, 5 or 6.

[0086] In the present application, the cycle number c1 of the first formation stage is preferably not more than the cycle number c2 of the second formation stage.

[0087] By making the cycle number of the first formation stage and the second formation stage in the above range, it is helpful to activate the negative electrode and self-repair the interface, and to build a more stable SEI film containing lithium components, that is, the sodium ion battery system can better generate a dense and stable SEI film, which is beneficial to improve the cycle stability of the sodium ion battery. If the cycle number of the first formation stage is greater than 4 cycles, the initial sodium ion pre-SEI is consumed too much, and the initial SEI is too thick, which also affects the later lithium ion self-repair SEI, thereby causing the polarization to increase, affecting the overall performance of the sodium ion battery. If the cycle number of the second formation stage is greater than 6 cycles, it will cause too much lithium to repair the SEI, which cannot repair sodium well, the initial capacity is affected, and the repaired SEI is too thick, the polarization increases, affecting the electrochemical performance of the sodium ion battery.

[0088] In the present application, on the basis of meeting the above voltage conditions, the temperature of the first formation stage and the second formation stage is further limited.

[0089] In some embodiments, in the first formation stage, that is, in the first charge-discharge condition, the ambient temperature in steps S10 to S30 is T1, and the T1 satisfies: T1≤45℃. Preferably, T1 is 45℃.

[0090] In some embodiments, in the second formation stage, that is, in the second charge-discharge condition, the ambient temperature in steps S40 to S60 is T2, and the T2 satisfies: T2≥60℃. Preferably, T2 is 60℃.

[0091] By making the temperature of the first formation stage and the second formation stage in the above range, it is helpful to activate the negative electrode and self-repair the interface, and to build a more stable SEI film containing lithium components, that is, the sodium ion battery system can better generate a dense and stable SEI film, which is beneficial to improve the cycle stability of the sodium ion battery. If the temperature of the first formation stage is greater than 45℃, it will cause the initial SEI to be unstable, the sodium ion to consume and repair the SEI, causing the initial capacity to decrease, and affecting the overall performance of the sodium ion battery. If the temperature of the second formation stage is less than 60℃, it will cause the original sodium-containing components to be unable to ablate, causing the lithium ion to be unable to repair the SEI well, thereby affecting the later cycle performance of the sodium ion battery.

[0092] In some embodiments, the positive electrode sheet includes a current collector and a positive electrode active material layer provided on at least one surface of the current collector in the thickness direction, the positive electrode active material layer includes a sodium ion positive electrode material and a lithium ion positive electrode material, and further, the positive electrode active material layer can further include a binder and a conductive agent. That is, the positive electrode active material layer includes a sodium ion positive electrode material, a lithium ion positive electrode material, a binder, and a conductive agent.

[0093] In the present application, by adding a certain amount of lithium ion positive electrode material such as lithium iron phosphate into the slurry for blending, and cooperating with the special charge-discharge platform voltage of the positive electrode, in-situ self-repair and construction of high-stability SEI film are completed.

[0094] Optionally, the mass ratio of the lithium ion positive electrode material in the positive electrode active material layer is 0.3% to 5%, that is, the mass fraction of the lithium ion positive electrode material is 0.3% to 5% based on the total mass of the positive electrode active material layer, and preferably, the mass fraction of the lithium ion positive electrode material is 0.5% to 1%. For example, the mass fraction of the lithium ion positive electrode material can be 0.3%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 5%, etc., and the specific value is not limited.

[0095] By making the blending amount of the lithium ion positive electrode material within the above suitable range, sufficient lithium source can be provided to repair the interface and supplement lithium. If the blending amount of the lithium ion positive electrode material is too low, the amount of lithium source provided is small, which may weaken the effect of repairing the interface and supplementing lithium. If the blending amount of the lithium ion positive electrode material is too high, although sufficient lithium source can be provided to repair the interface and supplement lithium, too much lithium ion positive electrode material will cause the total capacity to be low, and too much lithium will also affect the sodium insertion of the negative electrode.

[0096] In some embodiments, in the positive electrode active material layer, the mass ratio of the sodium ion positive electrode material, the conductive agent and the binder is (85-99):(0.5-5):(0.5-5). Optionally, the mass ratio of the sodium ion positive electrode material, the conductive agent and the binder is (90-97):(1-3):(0.5-2).

[0097] It should be noted that the type and mass content of the conductive agent and the binder in the positive electrode active material layer are not particularly limited in the present application, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0098] In some embodiments, the sodium ion positive electrode material includes a layered oxide sodium ion positive electrode material.

[0099] For example, the sodium ion positive electrode material can be a ternary layered sodium ion positive electrode material, or can be a binary layered sodium ion positive electrode material, or can be a multi-element layered sodium ion positive electrode material.

[0100] In some embodiments, the chemical formula of the layered oxide sodium ion positive electrode material is Na x TMO2, wherein TM represents at least one element of Ti, Ni, Mn, Fe, V, Cr, Co, Cu, Zn or Li, and x≥1 / 3, for example, x can be 2 / 3.

[0101] For example, the above-mentioned layered oxide sodium ion positive electrode material includes, but is not limited to, Na2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3O2, Na 2 / 3 Ni 1 / 6 Mn 1 / 2 Fe 1 / 3 O2, Na 2 / 3 Ni 1 / 3 Mn 2 / 3 One or more of O2.

[0102] In some embodiments, a sodium-ion battery is also provided, the sodium-ion battery comprising a battery prepared by the formation method of a sodium-ion battery as described above.

[0103] The sodium-ion battery of the present invention has the technical advantages of the sodium-ion battery using the aforementioned formation process, which can improve the instability of the SEI film in sodium-ion batteries and improve the cycle life of sodium-ion batteries.

[0104] It should be understood that all the features and advantages described above regarding the "formation method of sodium-ion batteries" also apply to this "sodium-ion battery", and will not be repeated here.

[0105] It should also be understood that the sodium-ion battery also includes a negative electrode, a separator, and an electrolyte. This application does not impose any particular restrictions on the specific type and structure of the negative electrode, separator, and electrolyte. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0106] The following describes the implementation methods of this application. The implementation methods described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the implementation methods, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents, materials, or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0107] Example 1

[0108] 1. Preparation of positive electrode sheet

[0109] Sodium ion cathode material (Na) 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3O2), binder polyvinylidene fluoride (PVDF) and conductive carbon black are mixed in a mass ratio of 97:2:1, lithium ion positive electrode material lithium iron phosphate (LFP) is added, the blending amount of LFP, i.e. the mass percentage of LEP in the positive electrode active material layer, is 0.3%, N-methyl pyrrolidone (NMP) is further added, and stirring is carried out under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on the current collector aluminum foil; the coated aluminum foil is baked in an oven with 5 different temperature gradients, then dried in an oven at 120°C for 8h, and then subjected to rolling, slitting to obtain the required positive electrode sheet.

[0110] 2. Preparation of negative electrode sheet

[0111] The negative electrode active material hard carbon, thickening agent sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, and conductive agent acetylene black are uniformly dispersed in deionized water in a mass ratio of 97:1:1:1, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a high-strength carbon-coated aluminum foil to obtain an electrode sheet; the obtained electrode sheet is dried at room temperature, then transferred to a 80°C oven for drying for 10h, and then subjected to rolling, slitting to obtain a negative electrode sheet.

[0112] 3. Preparation of electrolyte

[0113] In an inert gas-filled glove box (H2O < 10 ppm, O2 < 5 ppm), propylene carbonate (PC) and methyl ethyl carbonate (EMC) are configured in a mass ratio of 30:70, and 1 mol / L NaPF6 and 0.5wt% of fluoroethylene carbonate (FEC), 0.5wt% of methyldisulfonate (MMDS) and 0.5wt% of tris(trimethylsilyl)borate (TMSB) are added to obtain a conventional sodium lithium battery electrolyte.

[0114] 4. Preparation of separator film

[0115] A 9μm thick polypropylene (PP) film is used as the separator film.

[0116] 5. Preparation of sodium ion battery

[0117] The above positive electrode sheet, separator film and negative electrode sheet are stacked in order, with the separator film between the positive and negative electrode sheets to play a separating role, the bare cell is packaged in an aluminum plastic film, and a 3Ah soft package cell is prepared; the above prepared electrolyte is injected into the dried battery, and the battery is packaged, left to stand and formed, then subjected to secondary packaging, left to stand and divided, and the preparation of the lithium ion soft package battery is completed, wherein the specific operation steps of formation are shown in Table 1, and the specific conditions of formation are shown in Table 2.

[0118] The blending addition amount of the lithium ion positive electrode material LFP, the first charge and discharge conditions and the second charge and discharge conditions of the first formation stage and the second formation stage in Examples 2 to 15 (Examples 2 to 3 mainly adjust the blending addition amount of LFP, Examples 4 to 5 mainly adjust the cycle number c1 of the first formation stage, Examples 6 to 7 mainly adjust the cycle number c2 of the second formation stage, Examples 8 to 9 mainly adjust the current I1 of the first formation stage and the current I2 of the second formation stage, Examples 10 to 11 mainly adjust the temperature T1 of the first formation stage and the temperature T2 of the second formation stage, Examples 12 to 13 mainly adjust the voltage of the first formation stage, and Examples 14 to 15 mainly adjust the voltage of the second formation stage) are adjusted, and other parameters remain basically the same as in Example 1 or Example 2. The specific parameters are shown in Table 2.

[0119] The blending addition amount of the lithium ion positive electrode material LFP, the first charge and discharge conditions and the second charge and discharge conditions of the first formation stage and the second formation stage in Comparative Examples 1 to 11 (Comparative Example 1 adopts a conventional formation method, Comparative Example 2 omits the first formation stage, Comparative Example 3 omits the second formation stage, Comparative Example 4 omits the lithium ion positive electrode material LFP, Comparative Examples 5 to 7 mainly adjust the currents I1 and I2, Comparative Examples 8 to 9 mainly adjust the cycle numbers c1 and c2, and Comparative Examples 10 to 11 mainly adjust the temperatures T1 and T2) are adjusted, and other parameters remain basically the same as in Example 2. The specific parameters are shown in Table 2.

[0120] Table 1: Steps of formation

[0121]

[0122] Table 2: Blending positive electrode and formation setting conditions of each example and comparative example

[0123]

[0124]

[0125] Performance test

[0126] The batteries prepared in Examples 1 to 15 and Comparative Examples 1 to 11 were subjected to high-temperature cycle tests, and the specific test method was as follows:

[0127] High-temperature cycle test: under the condition of a temperature of 45℃, first 1C constant current charging to 4.0V, standing, then 1C constant current discharging to 2.0V, recording the discharge capacity of the 1st cycle as the initial capacity, such cycle charging and discharging, recording the cycle number corresponding to the reduction of the discharge capacity to 80% of the initial capacity, and recording the discharge capacity at the corresponding cycle number as the end capacity.

[0128] The test results are shown in Table 3.

[0129] Table 3: Battery performance test results of each example and comparative example

[0130]

[0131]

[0132] From the data of Table 2 and Table 3 above, it can be seen that, in general, the sodium-ion batteries prepared in Examples 1-15 of the present application have better capacity and cycle performance than those prepared in Comparative Examples 1-11, because the two-stage formation process provided by the present application is adopted in Examples 1-15, and the doping amount of the lithium-ion cathode material, the charge and discharge conditions in the first formation stage and the second formation stage are within the limited range of the present application.

[0133] Specifically, from the analysis and comparison of Examples 1-3, it can be seen that, by doping a lithium-ion cathode material such as lithium iron phosphate in the positive electrode sheet, and making the doping amount of lithium iron phosphate within the suitable range limited by the present application, sufficient lithium source can be provided to repair the interface and supplement lithium, which is beneficial to improving the cycle performance of the battery. In comparison, the more appropriate lithium iron phosphate doping amount of Example 2 can provide more sufficient lithium source to repair the interface and supplement lithium, the lower lithium iron phosphate doping amount of Example 1 can provide a small amount of lithium source to repair the interface and supplement lithium, and the higher lithium iron phosphate doping amount of Example 3 can provide a high amount of lithium source to repair the interface and supplement lithium, but too much lithium iron phosphate will cause the total capacity to be low, and too much lithium will also affect the sodium intercalation of the negative electrode.

[0134] From the analysis and comparison of Examples 2, 4-7, it can be seen that, the cycle number of the first formation stage of Example 4 is less than that of the first formation stage of Example 2, the negative electrode is not fully activated, which has a certain influence on the long-term performance of the battery, i.e. less cycle number of the first formation stage will reduce the long-term cycle performance; the cycle number of the first formation stage of Example 5 is greater than that of the first formation stage of Example 2, the initial Na-ion pre-formed SEI is consumed too much, the initial capacity is affected, i.e. more cycle number of the first formation stage will reduce the initial capacity. The cycle number of the second formation stage of Example 6 is less than that of the second formation stage of Example 2, the self-repairing SEI is not stable enough, which has an influence on the later long cycle of the battery, i.e. less cycle number of the second formation stage will reduce the long-term cycle performance; the cycle number of the second formation stage of Example 7 is greater than that of the second formation stage of Example 2, which causes high content of lithium to repair the SEI and cannot supplement sodium well, the initial capacity is affected, i.e. more cycle number of the second formation stage will reduce the initial capacity.

[0135] From the analysis and comparison of Example 2, Examples 8-9, it can be seen that the first formation stage current of Example 8 is increased, there is incomplete negative electrode activation, which has a certain influence on the long-term cycle performance of the battery; the second formation stage current of Example 9 is reduced, causing high content lithium to repair SEI, which cannot repair sodium well, and the initial capacity is affected. However, overall, the currents of Examples 8-9 are within the range defined in the application, and the cycle performance and initial capacity are better than the effects of the comparative examples.

[0136] From the analysis and comparison of Example 2, Examples 10-11, it can be seen that the temperature of the first formation stage of Example 10 is reduced, and the temperature of the second formation stage of Example 11 is increased, and the overall temperature is within the range defined, which has little effect on the initial capacity and cycle performance of the battery, and the cycle performance and initial capacity are better than the effects of the comparative examples.

[0137] From the analysis and comparison of Example 2, Examples 12-15, it can be seen that Example 12 uses a lower upper limit voltage in the first formation stage, which results in less sodium being removed, incomplete negative electrode activation, and a certain influence on the long-term cycle performance of the battery. Example 13 uses a higher upper limit voltage in the first formation stage, which results in simultaneous removal of sodium / lithium ions, affecting negative electrode activation and SEI repair, and significantly affecting the overall performance of the battery. Example 14 uses a lower upper limit voltage in the second formation stage, which will result in excessive sodium removal from the negative electrode, which will have a certain influence on the negative electrode activation. In addition, the upper limit voltage V2 of the first formation stage of Example 13 is not within the preferred range of the application (2.9V≤V2<3V), and the lower limit voltage V3 of the second formation stage of Example 14 is not within the preferred range of the application (3V≤V3<3.3V), resulting in the initial capacity and cycle performance of Examples 13 and 14 being worse than the rest of the examples, but overall, the initial capacity and cycle performance of Examples 13 and 14 are better than most of the comparative examples in Comparative Examples 1-11.

[0138] In addition, Example 15 uses a higher upper limit voltage in the second formation stage, which causes more sodium / lithium to be removed simultaneously, affecting the self-repairing SEI, and the capacity and cycle performance are worse than the effects of Example 2.

[0139] Comparative Example 1 adopts a conventional formation method, and has problems of inability to repair sodium in situ and to construct a stable SEI, and the capacity and cycle are affected, i.e., compared with Example 2, the capacity and cycle performance of Comparative Example 1 are obviously poorer than those of Example 2. Comparative Example 2 is a blank group, and the capacity and cycle performance are reduced because no lithium ion cathode material is added. Comparative Example 3 omits the first formation stage, resulting in no activation of the negative electrode, and lithium ions participate in repairing the SEI and also embed into the negative electrode, affecting the subsequent embedding of sodium ions, and reducing the capacity and cycle performance. Comparative Example 4 omits the second formation stage, resulting in that the SEI cannot be fully repaired, the cycle decay is fast, and the cycle performance is greatly reduced.

[0140] Compared with Example 2, the current of the first formation stage of Comparative Example 5 is smaller and is not within the scope of the application, resulting in complete release of initial Na ions, excessive consumption of preformed SEI, and affected initial capacity, i.e., reduced initial capacity. The current of the first formation stage of Comparative Example 6 is larger and is not within the scope of the application, resulting in less release of sodium ions due to polarization, incomplete activation of the negative electrode, and certain influence on long-term performance, i.e., reduced cycle performance. The current of the second formation stage of Comparative Example 7 is larger and is not within the scope of the application, resulting in that lithium ions cannot repair the SEI in time, the SEI is not stable enough, and the later cycle effect is affected.

[0141] Compared with Example 2, the cycle number of the first formation stage of Comparative Example 8 is too much and is within the scope of the application, resulting in excessive consumption of initial Na ions preformed SEI, and thicker initial SEI, also affecting the later lithium ion self-repairing SEI, thereby increasing polarization and affecting overall performance. The cycle number of the second formation stage of Comparative Example 9 is too much, causing excessive lithium to repair the SEI, inability to repair sodium well, affected initial capacity, and too thick repaired SEI, increasing polarization and affecting the overall performance of the battery.

[0142] Compared with Example 2, the temperature of the first formation stage of Comparative Example 10 is higher and is within the scope of the application, causing unstable initial SEI, consumption of sodium ions to repair the SEI, resulting in decreased initial capacity and affected long-term cycle performance. The temperature of the second formation stage of Comparative Example 11 is lower and is within the scope of the application, causing that the original sodium-containing components cannot be ablated, resulting in that lithium ions cannot repair the SEI well, thereby affecting the later cycle performance.

[0143] The part of the application not described in detail is the technology known to those skilled in the art.

[0144] The above describes the basic principles of the present application in combination with specific embodiments, but it should be noted that the advantages, benefits, effects and the like mentioned in the present application are only examples and are not limiting, and these advantages, benefits, effects and the like cannot be considered as necessary for each embodiment of the present application. In addition, the above specific details disclosed are only for the purpose of example and understanding, and are not limiting, and the above details do not limit the present application to the above specific details.

[0145] It should be noted that the term "and / or" or " / " used herein is only to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. The singular form "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural form, unless the context clearly indicates otherwise.

[0146] In the detailed description and claims, a list of items connected by the term "at least one of", "at least one", "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A formation method of a sodium-ion battery, characterized by, The sodium ion battery comprises a positive electrode sheet, the positive electrode sheet comprises a sodium ion positive electrode material and a lithium ion positive electrode material, the lithium ion positive electrode material comprises lithium iron phosphate and / or lithium manganese iron phosphate; The formation method comprises the following steps: The sodium ion battery to be formed is subjected to a constant current charging and discharging cycle according to a first charging and discharging condition to complete a first formation stage; The sodium ion battery completing the first formation stage is subjected to a constant current charging and discharging cycle according to a second charging and discharging condition to complete a second formation stage; The voltage in the first charging and discharging condition is less than the voltage in the second charging and discharging condition; In the first charging and discharging condition, the lower limit voltage is V1 and the upper limit voltage is V2, the V1 satisfies 1.5V≤V1≤2V, and the V2 satisfies 2.9V≤V2<3V; In the second charging and discharging condition, the lower limit voltage is V3 and the upper limit voltage is V4, the V3 satisfies 3V≤V3<3.3V, and the V4 satisfies 3.3V≤V4<3.4V.

2. The formation method of a sodium-ion battery according to claim 1, characterized in that, In the first charging and discharging condition, the charging current and the discharging current are both I1, the I1 satisfies 0.1C<I1≤0.3C; and / or, In the second charging and discharging condition, the charging current and the discharging current are both I2, the I2 satisfies I2≤0.1C. 3.The formation method of the sodium-ion battery according to claim 2, characterized in that, In the first charging and discharging condition, the number of cycles is c1, the c1 satisfies 2≤c1≤4; and / or, In the second charging and discharging condition, the number of cycles is c2, the c2 satisfies 4≤c2≤6.

4. The formation method of a sodium-ion battery according to claim 3, characterized in that, The ambient temperature in the first charging and discharging condition is T1, the T1 satisfies T1≤45℃; and / or, The ambient temperature in the second charging and discharging condition is T2, the T2 satisfies T2≥60℃. 5.The formation method of the sodium-ion battery according to claim 4, characterized in that, The first formation stage specifically comprises: S10, the sodium ion battery to be formed is subjected to a first static placement at a temperature T1; S20, the sodium ion battery after the first static placement is completed is subjected to a second static placement after being charged at a current I1 to a voltage V2 at the temperature T1; S30, the sodium ion battery after the second static placement is completed is subjected to a third static placement after being discharged at the current I1 to the voltage V1 at the temperature T1; The above steps S10 to S30 are cycled for c1 times to complete the first formation stage. 6.The formation method of the sodium-ion battery according to claim 4, characterized in that, The second formation stage specifically comprises: S40, the sodium ion battery completing the first formation stage is subjected to a fourth static placement at a temperature T2; S50, the sodium ion battery after the fourth static placement is completed is subjected to a fifth static placement after being charged at a current I2 to a voltage V4 at the temperature T2; S60, the sodium ion battery after the fifth static placement is completed is subjected to a sixth static placement after being discharged at the current I2 to the voltage V3 at the temperature T2; The above steps S40 to S60 are cycled for c2 times to complete the second formation stage.

7. A sodium-ion battery, characterized in that, The sodium ion battery comprises a battery prepared by the formation method of the sodium ion battery according to any one of claims 1 to 6.

8. The sodium-ion battery of claim 7, wherein, The positive plate in the sodium ion battery comprises a current collector and a positive active material layer arranged on the surface of the current collector, the positive active material layer comprises a sodium ion positive material and a lithium ion positive material, and the mass ratio of the lithium ion positive material in the positive active material layer is 0.3%-5%; The positive active material layer further comprises a conductive agent and a binder, and the mass ratio of the sodium ion positive material, the conductive agent and the binder is (85-99):(0.5-5):(0.5-5).

9. The sodium-ion battery according to claim 7 or 8, characterized in that, The sodium ion positive material comprises a layered oxide sodium ion positive material. The layered oxidic sodium-ion positive electrode material has a chemical formula of Na x TMO2, wherein TM represents at least one element of Ti, Ni, Mn, Fe, V, Cr, Co, Cu, Zn or Li, and x≥1 / 3.

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