Formation method of sodium ion battery and sodium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a formation method of a sodium ion battery and the sodium ion battery. According to the formation method of the sodium-ion battery, the sodium-ion battery comprises a positive plate, the positive plate comprises a sodium-ion positive electrode material and a lithium-ion positive electrode material, and the lithium-ion positive electrode material comprises lithium iron phosphate and / or lithium iron manganese phosphate; the formation method comprises the following steps: performing constant-current charge-discharge circulation on a sodium ion battery to be formed according to a first charge-discharge condition to complete a first formation stage; performing constant-current charge-discharge circulation on the sodium-ion battery subjected to the first formation stage according to a second charge-discharge condition to complete a second formation stage; wherein the voltage in the first charging and discharging condition is less than or equal to the voltage in the second charging and discharging condition. According to the invention, in-situ self-repairing sodium supplement and high-stability SEI construction can be achieved, the high-temperature stability of the SEI membrane of the sodium-ion battery is improved, and the cycle performance of the sodium-ion battery is further improved.

Description

Technical Field

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

[0002] Sodium and lithium have similar physical and chemical properties, that is, the working principle of sodium-ion batteries is similar to that of lithium-ion batteries. Compared with lithium-ion batteries, sodium resources are abundant and not restricted by geographical conditions. Therefore, sodium-ion batteries with good low-temperature performance, high safety, low cost, abundant resources, and long-term large-scale storage have broad application prospects in the field of energy storage, and are expected to replace lithium-ion batteries and be widely used in the field of energy storage. However, in sodium-ion batteries, due to the low Lewis acidity of sodium complexes, the generated solid electrolyte interface film (SEI film) is unstable, especially at high temperatures, it will dissolve in carbonate solvents, the SEI film is destroyed, the electrolyte is in direct contact with the negative electrode interface, a negative reaction will occur, and a large amount of gas will be generated, which will lead to the deterioration of battery performance and the rapid consumption of active sodium.

[0003] In order to alleviate the above problems, a sodium ion battery electrolyte is proposed in the related art. By adding a lithium salt additive to the electrolyte, the inorganic compound of lithium is reduced on the negative electrode surface during the lithium salt formation process, so as to form a stable and strong inorganic SEI layer on the negative electrode surface, and solve the problem of SEI high temperature dissolution, so as to improve the high temperature performance and cycle performance of the sodium ion battery. However, there are still certain shortcomings in the above method. On the one hand, when more lithium salt additives are added to the electrolyte, a denser lithium inorganic compound SEI film is generated, which is bound to affect the transmission of sodium ions, increase the interfacial impedance of the battery, and have an adverse effect on the charge and discharge performance of the battery; on the other hand, due to the high sodium potential itself, while the lithium salt forms a film, the lithium ions will also be embedded in the negative electrode, thereby hindering the embedding of the negative electrode sodium ions in the formation stage, thereby affecting the activation and overall performance of the negative electrode material. In addition, the lithium salt additive added to the electrolyte is relatively expensive, and there is also a certain conflict with the market positioning of sodium ion batteries, and the addition of lithium salts does not directly play a role in supplementing the sodium source.

[0004] In view of this, this application is hereby filed. Summary of the invention

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

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

[0007] According to one aspect of the present application, an embodiment of the present application provides a formation method of a sodium ion battery, wherein the sodium ion battery comprises a positive electrode sheet, wherein the positive electrode sheet comprises a sodium ion positive electrode material and a lithium ion positive electrode material, wherein the lithium ion positive electrode material comprises lithium iron phosphate and / or lithium iron manganese phosphate;

[0008] The formation method comprises the following steps:

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

[0010] Performing a constant current charge and discharge cycle on the sodium ion battery that has completed the first formation stage according to the second charge and discharge condition to complete the second formation stage;

[0011] Wherein, the voltage in the first charge and discharge condition is ≤ the voltage in the second charge and discharge condition.

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

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

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

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

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

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

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

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

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

[0021] In some embodiments, the ambient temperature under the first charge and discharge condition is T1, and T1 satisfies: T1≤45°C.

[0022] In some embodiments, the ambient temperature under the second charge and discharge condition is T2, and T2 satisfies: T2 ≥ 60°C.

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

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

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

[0026] S30, discharging the sodium ion battery after the second standing at a temperature T1 with a constant current of I1 to a voltage of V1, and then standing 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 includes:

[0029] S40, placing the sodium ion battery that has completed the first formation stage at a temperature of T2 for a fourth time;

[0030] S50, charging the sodium ion battery after the fourth resting at a temperature T2 with a constant current of current I2 to a voltage V4, and then performing a fifth resting;

[0031] S60, discharging the sodium ion battery after the fifth rest at a temperature T2 with a constant current of current I2 to a voltage V3, and then resting for the 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, an embodiment of the present application provides a sodium ion battery, wherein the sodium ion battery includes a battery produced by the sodium ion battery formation method as described above.

[0034] In some embodiments, the positive electrode sheet in the sodium ion battery includes a current collector and a positive electrode active material layer arranged on the surface of the current collector, the positive electrode active material layer includes a sodium ion positive electrode material and a lithium ion positive electrode material, and the mass proportion 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 includes a conductive agent and a binder, and the mass ratio of the sodium ion positive electrode material, the conductive agent and the binder is (85-99): (0.5-5): (0.5-5).

[0036] In some embodiments, the sodium ion positive electrode material includes 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 the group consisting of Ti, Ni, Mn, Fe, V, Cr, Co, Cu, Zn and Li, and x ≥ 1 / 3.

[0038] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0039] In an embodiment of the present application, the provided sodium ion battery formation method can be used in the formation of a sodium ion battery, wherein the positive electrode sheet in the sodium ion battery comprises a sodium ion positive electrode material and a lithium ion positive electrode material, wherein the lithium ion positive electrode material comprises lithium iron phosphate and / or lithium iron manganese phosphate, and the formation comprises two stages, wherein the voltage of the first formation stage does not exceed the voltage of the second formation stage. Thus, the present invention adds a lithium ion positive electrode material to the positive electrode sheet of the sodium ion battery, and since the lithium delithiation potential of lithium ion positive electrode materials such as lithium iron phosphate and / or lithium iron manganese 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 de-sodiumized, thereby, 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 can be released on the positive electrode side in the first formation stage, and less lithium ions are released, and the sodium ions simultaneously participate in film formation and negative electrode sodium insertion activity. In the first formation stage, the unstable SEI film and negative electrode activation are pre-constructed; further, in the second formation stage, the voltage is relatively high, and lithium ions are mainly released on the positive electrode side in this stage, thereby providing a lithium source in situ in the sodium-electric system, and self-repairing the original unstable SEI, thereby forming a highly stable SEI layer, and will not affect the negative electrode sodium insertion activation; at the same time, the sodium ions dissolved from the SEI will be combined with the electrons released from the positive electrode of the lithium ion positive electrode material to embed into the negative electrode, thereby achieving in-situ self-repair sodium supplementation and highly stable SEI construction. As a result, the stability of the SEI film of the sodium ion battery is improved, which is conducive to improving the cycle performance of the sodium ion battery.

[0040] Additional aspects and advantages of the present application will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0041] The present application is further described below in conjunction with specific embodiments. It should be understood that these embodiments of the present application are only used to illustrate the present application and are not used to limit the scope of the present application.

[0042] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0043] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0044] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

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

[0046] In view of this, the inventor of this application starts from the perspective of improving the stability of the SEI film of the sodium ion battery and thus improving the cycle performance of the battery. After in-depth research, the inventor discovered and proposed to improve the existing sodium ion battery formation method, in order to provide a solution for in-situ self-repair sodium supplementation and high-stability SEI design of the sodium ion battery, so as to achieve the purpose of improving the stability of the SEI film, especially the stability of the SEI film at high temperature, and thus improve the cycle life of the battery. Next, this application is described in detail.

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

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

[0049] In the present application, a sodium ion battery formation method is provided, comprising the following steps:

[0050] Performing a constant current charge and discharge cycle on the sodium ion battery to be formed according to the first charge and discharge condition to complete the first formation stage;

[0051] Performing a constant current charge and discharge cycle on the sodium ion battery that has completed the first formation stage according to the second charge and discharge condition to complete the second formation stage;

[0052] The voltage in the first charge and discharge condition is ≤ the voltage in the second charge and discharge condition.

[0053] The above-mentioned formation can be divided into two stages, such as, 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 that has completed 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 may include charge and discharge conditions such as current, voltage, temperature, and number of cycles.

[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), so that different positive electrode materials can be deintercalated with lithium or sodium in different voltage ranges.

[0055] Generally, for different positive electrode active materials, sodium / lithium insertion and sodium / lithium removal have their own specific reaction potentials, which determines that each material has its own unique operating voltage range. The formation method described in the present invention is based on the electrochemical characteristics of the sodium ion battery system itself, and is mainly aimed at the instability of the conventional SEI film of the negative electrode of the sodium ion battery. A small amount of lithium ion positive electrode material is doped in the positive electrode sheet of the sodium ion battery, and is supplemented by a specific formation design. For example, the different voltage ranges of sodium and lithium deintercalation of sodium and lithium deintercalation of sodium ion positive electrode materials and lithium ion positive electrode materials are used to divide the formation into two stages, and the voltage ranges of the two stages are different, so as to perform in-situ self-repair of sodium supplementation and the construction of a highly stable SEI film on the negative electrode side. In detail:

[0056] In the embodiment of the present application, based on the problem of high solubility of the sodium complex components of the sodium electrolyte SEI, a small amount of lithium ion positive electrode material such as lithium iron phosphate and / or lithium iron manganese phosphate is doped in the positive electrode sheet of the sodium ion battery. Since the lithium delithiation potential of lithium ion positive electrode materials such as lithium iron phosphate and / or lithium iron manganese phosphate is higher than that of sodium ion positive electrode materials, the lithium ion positive electrode material will release lithium ions after the sodium ion positive electrode material is partially de-sodiumized. Thus, by setting two formation stages and setting the two-stage formation voltage, the formation voltage of the first formation stage is less than or equal to the formation voltage of the second formation stage. For example, the formation voltage range of the first formation stage can be 2V to 3V, and the formation voltage range of the second formation stage can be 3V ~3.4V, so that only sodium ions can be released on the positive electrode side in the first formation stage, and lithium ions are released less. Sodium ions simultaneously participate in the film formation of the negative electrode and the activation of negative electrode sodium insertion, thereby pre-building an unstable SEI film and negative electrode activation in the first formation stage; further, in the second formation stage, its voltage is relatively high, and lithium ions are mainly released on the positive electrode side in this stage, thereby providing a lithium source in situ in the sodium-electric system, and self-repairing the original unstable SEI, thereby forming a highly stable SEI layer, and will not affect the activation of negative electrode sodium insertion; at the same time, the sodium ions dissolved from the SEI will be combined with the electrons released from the positive electrode of the lithium ion positive electrode material to embed into the negative electrode, thereby achieving in-situ self-repair sodium supplementation and highly stable SEI film construction. Thereby, the stability of the SEI film of the sodium ion battery is improved, which is conducive to improving the cycle performance of the sodium ion battery.

[0057] Compared with the method of adding lithium salt additives to the electrolyte in the prior art, the method of the present invention does not directly add lithium salt to the electrolyte, so it will not affect the initial activation process of the sodium negative electrode. In addition, the present invention adds lithium iron phosphate and / or lithium iron manganese phosphate lithium ion positive electrode materials to the positive electrode sheet in advance, and with the help of a special formation potential design, it can be achieved that lithium is not removed in the early stage of formation, but only sodium is removed, thereby performing initial sodium negative electrode activation; in the later stage, the positive electrode removes a large amount of lithium and a small amount of sodium, and the removed lithium ions will repair the unstable SEI layer formed by the high-temperature dissolution of the sodium complex on the negative electrode side. At the same time, the sodium ions dissolved from the SEI film will be embedded in the negative electrode in combination with the electrons released from the lithium iron phosphate positive electrode to complete the in-situ sodium replenishment, thereby achieving in-situ self-repair sodium replenishment and highly stable SEI film construction of the sodium ion battery system.

[0058] In the present application, the lithium-ion positive electrode material adopts one or both of lithium iron phosphate or lithium iron manganese phosphate. Preferably, the lithium-ion positive electrode material is selected from lithium iron phosphate. This is because both lithium iron phosphate and lithium iron manganese phosphate have two corresponding stable lithium intercalation and deintercalation platforms, which is more conducive to the early stable SEI construction and sodium replenishment mechanism of the present application. Other lithium-ion positive electrode materials such as ternary materials use a stable release of lithium ions throughout the entire voltage range, which is not conducive to the early stable SEI construction and sodium replenishment mechanism of the present application. In addition, the lithium iron phosphate positive electrode material belongs to the olivine structure, has very excellent stability, and is conducive to improving the cycle performance of sodium-ion batteries.

[0059] In the present application, the sodium ion positive electrode material may adopt a layered sodium ion positive electrode material, and the operating voltages of the layered sodium ion positive electrode material and the lithium iron phosphate or lithium iron manganese phosphate positive electrode material satisfy a certain relationship. It should be noted that the voltage in the above-mentioned first charge and discharge condition needs to be less than or equal to the voltage in the second charge and discharge condition, and the specific range of voltage in the first charge and discharge condition and the specific range of voltage in the second charge and discharge condition can be adaptively adjusted according to the specific types of the specific sodium ion positive electrode material and lithium ion positive electrode material used. That is, depending on the specific types of the specific sodium ion positive electrode material and lithium ion positive electrode material used, the specific range value of the voltage in the first charge and discharge condition and the specific range value of the voltage in the second charge and discharge condition may be different.

[0060] In some embodiments, in the first charge and discharge condition of the first formation stage, the voltage ranges from 1.5V to 3V. Preferably, under normal conditions, the voltage ranges from 2V to 3V.

[0061] In some embodiments, in the second charge and discharge condition of the second formation stage, the voltage ranges from 3V to 3.4V, and further, the voltage ranges from 3V to 3.3V.

[0062] In the embodiment of the present application, the formation voltage of the first formation stage is preferably 2V~3V. In this stage, only sodium ions are released from the positive electrode side, and less lithium ions are released. Sodium ions are also involved in film formation and sodium insertion activation of the negative electrode, thereby pre-constructing an unstable SEI film and negative electrode activation; the formation voltage of the second formation stage is 3V~3.4V, or 3V~3.3V. In this stage, lithium ions are mainly released from the positive electrode side, thereby providing a lithium source in situ in the sodium-based system, and self-repairing the original unstable SEI, thereby forming a highly stable SEI layer, and will not affect the sodium insertion activation of the negative electrode; at the same time, the sodium ions dissolved from the SEI will be embedded in the negative electrode in combination with the electrons released from the lithium iron phosphate positive electrode, thereby achieving in-situ self-repair sodium supplementation and highly stable SEI construction.

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

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

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

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

[0067] The above steps S10 to S30 are repeated for 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 that has completed the first formation stage at a temperature of T2 for a fourth time;

[0070] S50, charging the sodium ion battery after the fourth resting at a temperature T2 with a constant current of current I2 to a voltage V4, and then performing a fifth resting;

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

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

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

[0074] In some embodiments, in the first formation stage, that is, 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 the above V1 is the lower limit of the discharge voltage of the sodium battery system. Usually, V1 is 2V, or in some special cases, depending on the different material type systems, V1 can also be 1.5V.

[0076] In some embodiments, in the second formation stage, that is, 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, and the value of V3 is set according to the lithium ion positive electrode material used, lithium iron phosphate or lithium manganese iron phosphate. Preferably, the value of V3 is 3V, and V4 satisfies: 3.3V≤V4<3.4V.

[0077] Therefore, by controlling the upper and lower voltage limits of the first formation stage and the second formation stage within the above range, it is helpful to prevent lithium from being removed in the early stage of formation (the first formation stage) and only remove sodium, thereby performing initial sodium negative electrode activation; in the late stage of formation (the second formation stage), the positive electrode removes a large amount of lithium and a small amount of sodium, and the removed lithium ions will repair the unstable SEI layer on the negative electrode side due to the high-temperature dissolution of the sodium complex. At the same time, the sodium ions dissolved from the SEI will combine with the electrons released from the lithium iron phosphate positive electrode to embed into the negative electrode, completing in-situ sodium replenishment, thereby achieving in-situ self-repair sodium replenishment and highly stable SEI film construction of the sodium ion battery system.

[0078] In the present application, on the basis of satisfying the above voltage conditions, there are further certain restrictions on the current magnitudes in the first formation stage and the second formation stage.

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

[0080] In some embodiments, in the second formation stage, that is, in the second charge and discharge condition, the current of the constant current charge and discharge in steps S50 and S60 is I2, and I2 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 it can also be less than 0.01C or other values ​​within this range. Preferably, I2 is 0.05C.

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

[0082] By making the current 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 ions are completely released, and 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 reasons, less sodium ions are released, and the negative electrode activation is incomplete, 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 ions will not have time to repair the SEI, which will cause the SEI to be unstable, 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 conditions, there are further certain restrictions on the number of cycles of the first formation stage and the second formation stage.

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

[0085] In some embodiments, in the first formation stage, that is, in the second charge and discharge condition, the number of cycles is c2, and c2 satisfies: 4≤c2≤6. For example, the number of cycles c2 in the second formation stage can be 4, 5 or 6.

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

[0087] By making the number of cycles of the first formation stage and the second formation stage within the above range, it is helpful to activate the negative electrode and the self-repairing interface, and construct 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 conducive to improving the cycle stability of the sodium ion battery. If the number of cycles of the first formation stage is greater than 4, the initial sodium ion pre-formation SEI is consumed too much, and the initial SEI is thick, which also affects the later lithium ion self-repair SEI, thereby increasing polarization and affecting the overall performance of the sodium ion battery. If the number of cycles of the second formation stage is greater than 6, too much lithium will repair the SEI, and sodium cannot be supplemented well, the initial capacity will be affected, and the repaired SEI is too thick, polarization will increase, and the electrochemical performance of the sodium ion battery will be affected.

[0088] In the present application, on the basis of satisfying the above voltage conditions, there are further certain restrictions on the temperatures of the first formation stage and the second formation stage.

[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 T1 satisfies: T1≤45° C. Preferably, T1 is 45° C.

[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 T2 satisfies: T2 ≥ 60° C. Preferably, T2 is 60° C.

[0091] By keeping the temperature of the first formation stage and the second formation stage within the above range, it is helpful to activate the negative electrode and the self-repairing interface, and construct 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°C, the initial SEI will be unstable, and the sodium ions will consume and repair the SEI, resulting in a decrease in the initial capacity and affecting the overall performance of the sodium ion battery. If the temperature of the second formation stage is less than 60°C, the original sodium-containing components will not be melted, resulting in the inability of lithium ions to self-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 disposed 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 may also 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, a certain amount of lithium iron phosphate and other lithium-ion positive electrode materials are added to the slurry for mixing, and the special charge and discharge platform voltage of the positive electrode is matched to complete in-situ self-repair and construct a high-stability SEI film.

[0094] Optionally, the mass fraction of the lithium ion positive electrode material in the positive electrode active material layer is 0.3% to 5%, that is, based on the total mass of the positive electrode active material layer, the mass fraction of the lithium ion positive electrode material is 0.3% to 5%, 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., without specific limitation.

[0095] By making the blending amount of the lithium-ion positive electrode material within the above-mentioned appropriate range, sufficient lithium source can be provided to repair the interface and replenish 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 replenishing lithium. If the blending amount of the lithium-ion positive electrode material is too high, although it can increase the sufficient lithium source to repair the interface and replenish 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 pointed out that the present application has no particular restrictions on the type and mass content of the conductive agent and binder in the positive electrode active material layer, and those skilled in the art can choose according to actual needs as long as the purpose of the present application can be achieved.

[0098] In some embodiments, the sodium ion cathode material includes a layered oxide-based sodium ion cathode material.

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

[0100] In some embodiments, the chemical formula of the layered oxide sodium ion cathode 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] As an example, the 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, wherein the sodium ion battery comprises a battery made by the sodium ion battery formation method as described above.

[0103] The sodium ion battery of the present invention has the technical advantages of the above-mentioned sodium ion battery using the aforementioned formation process, can improve the SEI membrane instability problem of the sodium ion battery, and can increase the cycle life of the sodium ion battery.

[0104] It should be understood that all the features and advantages described above for the "sodium ion battery formation method" are also applicable to the "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 sheet, a separator and an electrolyte. The present application has no particular restrictions on the specific types and structures of the negative electrode sheet, separator and electrolyte. Those skilled in the art can choose according to actual needs as long as the purpose of the present application can be achieved.

[0106] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this area or the product instructions are used. If the manufacturer of the reagents, materials or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0107] Example 1

[0108] 1. Preparation of positive electrode

[0109] The sodium ion positive electrode 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 mixing amount of LFP, that is, the mass proportion of LEP in the positive electrode active material layer is 0.3%, and then N-methylpyrrolidone (NMP) is added, and stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the current collector aluminum foil; the coated aluminum foil is baked in an oven with 5 different temperature gradients, and then dried in an oven at 120°C for 8 hours, and then rolled and cut to obtain the required positive electrode sheet.

[0110] 2. Preparation of negative electrode sheet

[0111] The negative electrode active material hard carbon, thickener 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 the negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is uniformly coated on a high-strength carbon-coated aluminum foil to obtain a pole piece; the obtained pole piece is dried at room temperature and then transferred to an oven at 80°C for drying for 10 hours, and then rolled and cut to obtain a negative electrode sheet.

[0112] 3. Preparation of electrolyte

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

[0114] 4. Prepare the isolation film

[0115] A polypropylene (PP) film with a thickness of 9 μm was used as the isolation film.

[0116] 5. Preparation of sodium ion batteries

[0117] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, ensuring that the separator is between the positive and negative electrode sheets to play an isolating role, and the bare battery cell is placed in an aluminum-plastic film outer package to prepare a 3Ah soft-pack battery cell; the prepared electrolyte is injected into the dried battery, packaged, allowed to stand, and formed, and then secondary packaging, standing, and capacity division are performed to complete the preparation of the lithium-ion soft-pack battery, wherein the specific operating steps of the formation are shown in Table 1, and the specific conditions of the formation are shown in Table 2.

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

[0119] In Comparative Examples 1 to 11, the blending amount of the lithium ion positive electrode material LFP, the first charge and discharge conditions in the first formation stage and the second charge and discharge conditions in the second formation stage are adjusted (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 number of cycles c1 and c2, and Comparative Examples 10 to 11 mainly adjust the temperatures T1 and T2), and other parameters are basically the same as those in Example 2. The specific parameters are shown in Table 2.

[0120] Table 1 Process steps of chemical formation

[0121]

[0122] Table 2 Mixed positive electrode and formation setting conditions of each embodiment and comparative example

[0123]

[0124]

[0125] Performance Testing

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

[0127] High temperature cycle test: At a temperature of 45°C, first charge to 4.0V at 1C constant current, let it stand, then discharge to 2.0V at 1C constant current, record the discharge capacity of the first cycle as the initial capacity, and repeat the charge and discharge cycle, record the number of cycles when the discharge capacity decreases to 80% of the initial capacity, and record the discharge capacity when the cycle reaches the corresponding number of cycles as the end capacity.

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

[0129] Table 3 Battery performance test results of various embodiments and comparative examples

[0130]

[0131]

[0132] Combining the data in Table 2 and Table 3 above, it can be seen that, in general, Examples 1 to 15 of the present invention adopt the two-stage formation process provided by the present invention, and the doping amount of the lithium ion positive electrode material, the charge and discharge conditions of the first formation stage and the second formation stage are within the specified range of the present invention, so that the capacity and cycle performance of the sodium ion batteries prepared in Examples 1 to 15 of the present invention are better than those in Comparative Examples 1 to 11.

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

[0134] From the analysis and comparison of Example 2 and Examples 4 to 7, it can be seen that the number of cycles in the first formation stage of Example 4 is less than the number of cycles in the first formation stage of Example 2, and the negative electrode activation is incomplete, which has a certain impact on the long-term performance of the battery, that is, fewer cycles in the first formation stage will reduce the long-term cycle performance; the number of cycles in the first formation stage of Example 5 is greater than the number of cycles in the first formation stage of Example 2, and the initial Na ions are consumed too much to pre-form SEI, and the initial capacity is affected, that is, more cycles in the first formation stage will reduce the initial capacity. The number of cycles in the second formation stage of Example 6 is less than the number of cycles in the second formation stage of Example 2, and the self-repairing SEI is not stable enough, which has an impact on the later long cycle of the battery, that is, fewer cycles in the second formation stage will reduce the long-term cycle performance; the number of cycles in the second formation stage of Example 7 is greater than the number of cycles in the second formation stage of Example 2, resulting in high-content lithium repairing SEI, unable to supplement sodium well, and the initial capacity is affected, that is, more cycles in the second formation stage will reduce the initial capacity.

[0135] From the analysis and comparison of Example 2 and Examples 8 to 9, it can be seen that the current in the first formation stage of Example 8 increases, and there is incomplete negative electrode activation, which has a certain impact on the long-term cycle performance of the battery; the current in the second formation stage of Example 9 decreases, resulting in high-content lithium repairing SEI, unable to supplement sodium well, and the initial capacity is affected. However, in general, the currents of Examples 8 to 9 are all within the range defined by the present invention, and their cycle performance and initial capacity are better than those of the comparative example.

[0136] From the analysis and comparison of Example 2 and Examples 10 to 11, it can be seen that the temperature of the first formation stage of Example 10 decreases, and the temperature of the second formation stage of Example 11 increases, and the overall temperature is within the specified range, which has little effect on the initial capacity and cycle performance of the battery, and its cycle performance and initial capacity are better than those of the comparative example.

[0137] From the analysis and comparison of Example 2 and Examples 12 to 15, it can be seen that the first formation stage of Example 12 adopts a lower upper limit voltage, resulting in less sodium detachment and incomplete activation of the negative electrode, which has a certain impact on the long-term cycle performance of the battery. The first formation stage of Example 13 adopts a higher upper limit voltage, resulting in the simultaneous detachment of sodium / lithium ions, which has an impact on the activation of the negative electrode and SEI repair, so that the overall performance of the battery is significantly affected. The second formation stage of Example 14 adopts a lower upper limit voltage, which will cause excessive sodium removal from the negative electrode, which has a certain impact on the activation of the negative electrode. In addition, the upper limit voltage V2 of the first formation stage of Example 13 is not within the preferred range of the present invention (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 present invention (3V≤V3<3.3V), resulting in the initial capacity and cycle performance of Examples 13 and 14 being worse than the other 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, the second formation stage of Example 15 adopts a higher upper limit voltage, and more sodium / lithium is released simultaneously, which affects the self-repairing SEI, resulting in the capacity and cycle performance being worse than those of Example 2.

[0139] Comparative Example 1 adopts a conventional formation method, and there is a problem that it cannot self-repair in situ to supplement sodium and construct a highly stable SEI, and both the capacity and cycle are affected. That is, compared with Example 2, the capacity and cycle performance of Comparative Example 1 are significantly inferior to those of Example 2. Comparative Example 2 is a blank group, and no lithium ion positive electrode material is added, which reduces the capacity and cycle performance. Comparative Example 3 omits the first formation stage, resulting in no activation of the negative electrode. Lithium ions participate in the repair of SEI and are also embedded in the negative electrode, affecting the subsequent embedding of sodium ions, reducing the capacity and cycle performance. Comparative Example 4 omits the second formation stage, resulting in the inability of SEI to fully self-repair, the cycle decay is relatively fast, and the cycle performance is greatly reduced.

[0140] Compared to Example 2, the current of the first formation stage of Comparative Example 5 is smaller, and is not within the scope of the present invention, resulting in the complete release of initial Na ions, excessive consumption of pre-formed SEI, and the initial capacity being affected, i.e., reducing the initial capacity. The current of the first formation stage of Comparative Example 6 is larger, and is not within the scope of the present invention, resulting in less sodium ion release due to polarization reasons, incomplete activation of the negative electrode, and a certain impact on long-term performance, i.e., reducing the cycle performance. The current of the second formation stage of Comparative Example 7 is larger, and is not within the scope of the present invention, resulting in lithium ions being too late to repair SEI, causing SEI to be unstable, affecting the later cycle effect.

[0141] Compared with Example 2, the number of cycles in the first formation stage of Comparative Example 8 is too much, and within the scope of the present invention, the initial Na ions are consumed too much to pre-form SEI, and the initial SEI is thick, which also affects the later lithium ions to self-repair SEI, thereby increasing polarization and affecting the overall performance. The number of cycles in the second formation stage of Comparative Example 9 is too much, resulting in too much lithium repairing SEI, unable to supplement sodium well, the initial capacity is affected, and the repaired SEI is too thick, polarization increases, and the overall performance of the battery is affected.

[0142] Compared with Example 2, the temperature of the first formation stage of Comparative Example 10 is higher, and within the scope of the present invention, causing the initial SEI to be unstable, sodium ions to consume and repair SEI, resulting in a decrease in initial capacity and affecting long-term cycle performance. The temperature of the second formation stage of Comparative Example 11 is lower, and within the scope of the present invention, causing the original sodium-containing components to be unable to be dissolved, resulting in the inability of lithium ions to self-repair SEI well, thereby affecting the later cycle performance.

[0143] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0144] The basic principle of the present invention is described above in conjunction with specific embodiments. However, it should be pointed out that the advantages, strengths, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. must be possessed by each embodiment of the present invention. In addition, the specific details disclosed above are only for the purpose of illustration and facilitation of understanding, rather than limitation, and the above details do not limit the present invention to being implemented by adopting the above specific details.

[0145] It should be noted that the term "and / or" or " / " used in this document is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The singular forms of "a", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0146] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may 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 may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may 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 invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium ion battery formation method, characterized in that: The sodium ion battery comprises a positive electrode sheet, wherein the positive electrode sheet comprises a sodium ion positive electrode material and a lithium ion positive electrode material, wherein the lithium ion positive electrode material comprises lithium iron phosphate and / or lithium iron manganese phosphate; The formation method comprises the following steps: Performing a constant current charge and discharge cycle on the sodium ion battery to be formed according to the first charge and discharge condition to complete the first formation stage; Performing a constant current charge and discharge cycle on the sodium ion battery that has completed the first formation stage according to the second charge and discharge condition to complete the second formation stage; Wherein, the voltage in the first charge and discharge condition is ≤ the voltage in the second charge and discharge condition.

2. The sodium ion battery formation method according to claim 1, characterized in that: In the first charge and discharge condition, the lower limit voltage is V1, the upper limit voltage is V2, V1 satisfies: 1.5V≤V1≤2V, V2 satisfies: 2.9V≤V2<3V; and / or, In the second charge and discharge condition, the lower limit voltage is V3, the upper limit voltage is V4, V3 satisfies: 3V≤V3<3.3V, and V4 satisfies: 3.3V≤V4<3.4V.

3. The sodium ion battery formation method according to claim 1, characterized in that: In the first charge and discharge condition, the charging current and the discharging current are both I1, and I1 satisfies: 0.1C<I1≤0.3C; and / or, In the second charge and discharge condition, the charging current and the discharging current are both I2, and I2 satisfies: I2≤0.1C.

4. The sodium ion battery formation method according to claim 1, characterized in that: In the first charge and discharge condition, the number of cycles is c1, and c1 satisfies: 2≤c1≤4; and / or, In the second charge and discharge condition, the number of cycles is c2, and c2 satisfies: 4≤c2≤6.

5. The sodium ion battery formation method according to claim 1, characterized in that: The ambient temperature under the first charge and discharge condition is T1, and T1 satisfies: T1≤45°C; and / or, The ambient temperature under the second charge and discharge condition is T2, and T2 satisfies: T2 ≥ 60°C.

6. The sodium ion battery formation method according to any one of claims 1 to 5, characterized in that: The first formation stage specifically includes: S10, allowing the sodium ion battery to be formed to stand for the first time at a temperature of T1; S20, charging the sodium ion battery after the first standing at a temperature T1 with a constant current I1 to a voltage V2, and then standing for a second time; S30, discharging the sodium ion battery after the second standing at a temperature T1 with a constant current of I1 to a voltage of V1, and then standing for a third time; The above steps S10 to S30 are repeated for c1 times to complete the first formation stage.

7. The sodium ion battery formation method according to any one of claims 1 to 5, characterized in that: The second formation stage specifically includes: S40, placing the sodium ion battery that has completed the first formation stage at a temperature of T2 for a fourth time; S50, charging the sodium ion battery after the fourth resting at a temperature T2 with a constant current of current I2 to a voltage V4, and then performing a fifth resting; S60, discharging the sodium ion battery after the fifth rest at a temperature T2 with a constant current of current I2 to a voltage V3, and then resting for the sixth time; The above steps S40 to S60 are repeated for c2 times to complete the second formation stage.

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

9. The sodium ion battery according to claim 8, characterized in that: The positive electrode sheet in the sodium ion battery includes a current collector and a positive electrode active material layer disposed on the surface of the current collector, wherein the positive electrode active material layer includes a sodium ion positive electrode material and a lithium ion positive electrode material, and the mass proportion of the lithium ion positive electrode material in the positive electrode active material layer is 0.3% to 5%; Preferably, the positive electrode active material layer further includes a conductive agent and a binder, and the mass ratio of the sodium ion positive electrode material, the conductive agent and the binder is (85-99): (0.5-5): (0.5-5).

10. The sodium ion battery according to claim 8 or 9, characterized in that: The sodium ion positive electrode material includes a layered oxide type sodium ion positive electrode material; Preferably, 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 the group consisting of Ti, Ni, Mn, Fe, V, Cr, Co, Cu, Zn and Li, and x ≥ 1 / 3.

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