Sodium ion battery based on titanium-based phosphate negative electrode

Abstract

The invention discloses a titanium-based phosphate negative electrode-based sodium ion battery, which comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm, the positive electrode comprises a polyanion material with a sodium super-ion conductor structure, the negative electrode comprises potassium titanyl phosphate, and the structural general formula of a functional additive contained in the electrolyte is # imgabs0 #, r1, R2 and R3 are independently selected from one of halogen atoms, oxygen atoms, hydroxyl groups, amino groups and C1-C10 alkyl groups. According to the invention, the functional additive is added into the electrolyte of the sodium-ion battery, a specific activation system is combined, and under the catalysis of the active substance, the self-polymerization reaction is carried out to form an effective protective layer, so that the direct contact between the electrolyte and the negative active substance is successfully blocked, and the catalytic decomposition effect of Ti ions in the negative active substance on the electrolyte is inhibited; the cycling stability of the sodium ion battery is effectively improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery based on a titanium-based phosphate negative electrode. Background Art

[0002] In the field of battery technology, the performance of negative electrode materials plays a vital role in the overall performance of the battery. Potassium titanyl phosphate (KTiOPO4), as a potential negative electrode material, faces some severe challenges in practical applications. Among them, the Ti ions in the negative electrode KTiOPO4 have an electrocatalytic effect, which easily causes the electrolyte to decompose and produce gas. This phenomenon not only reduces the capacity of the battery, but also causes an increase in the internal pressure of the battery, and may even bring safety hazards. In addition, the decomposition of the electrolyte will cause the internal resistance of the battery to increase, thereby reducing the battery's charge and discharge efficiency and cycle life.

[0003] In response to these problems, the existing solutions are mainly to improve the stability of the electrolyte and the stability of the negative electrode material by adding antioxidants and electrolyte additives. For example, antioxidants can be added to prevent the decomposition of the electrolyte, thereby reducing the generation of gas. However, the existing antioxidants and electrolyte additives can only delay the decomposition of the electrolyte, but cannot completely prevent the decomposition of the electrolyte. They cannot fundamentally and effectively solve the problem of titanium-catalyzed electrolyte decomposition and gas production in the negative electrode KTiOPO4, resulting in poor battery cycle stability, affecting battery life, and seriously restricting the widespread application and development of the negative electrode KTiOPO4 in the battery field. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a sodium ion battery based on a titanium-based phosphate negative electrode. Functional additives are added to the electrolyte of the sodium ion battery. Combined with a specific activation system, a self-polymerization reaction occurs under the catalysis of the negative electrode KTiOPO4 active substance, and an effective protective layer is formed on the surface of the negative electrode active substance, which successfully blocks the direct contact between the electrolyte and the negative electrode active substance, and fundamentally inhibits the catalytic decomposition of the electrolyte by Ti ions in the negative electrode active substance KTiOPO4, thereby specifically solving the problem of gas production by the decomposition of the electrolyte catalyzed by Ti ions. The battery is simple to operate, low in cost, and has a significant effect and is long-lasting and stable. The cycle stability of the sodium ion battery is effectively improved, the service life of the battery is extended, and strong technical support is provided for the wide application of the negative electrode KTiOPO4 in the battery field.

[0005] In order to solve the above technical problems, the present invention provides a sodium ion battery based on a titanium-based phosphate negative electrode, comprising a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, wherein the positive electrode comprises a polyanion material having a sodium superion conductor structure, the negative electrode comprises potassium titanyl phosphate, and the functional additive contained in the electrolyte has a general structural formula of:

[0006]

[0007] Wherein, R1, R2, and R3 are independently selected from one of a halogen atom, an oxygen atom, a hydroxyl group, an amino group, and a C1-C10 alkyl group.

[0008] The sodium ion battery of the present invention uses titanium-based phosphate KTiOPO4 as a negative electrode active material, adds a functional additive into the electrolyte, the functional additive has a carbon-carbon double bond and a carbonyl group adjacent to the carbon-carbon double bond, migrates to the surface of the negative electrode during charging, undergoes a self-polymerization reaction under the catalysis of the negative electrode KTiOPO4, forms a protective layer on the surface of KTiOPO4, avoids contact between KTiOPO4 and the electrolyte, and further prevents the negative electrode Ti ions from catalytically decomposing the electrolyte, improves the cycle stability of the battery, and prolongs the battery life; the present invention only needs to add a specific functional additive into the electrolyte, is simple to operate, low in cost, and has a significant effect and is long-lasting and stable; effectively improves the cycle stability of the sodium ion battery, prolongs the battery life, and provides strong technical support for the wide application of the negative electrode KTiOPO4 in the battery field.

[0009] Furthermore, the added amount of the functional additive is 0.1%-2% of the mass of the electrolyte, such as 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, etc., including but not limited to these.

[0010] Furthermore, the functional additive is selected from one or more of acrylamide, tetrahydrofurfuryl methacrylate, 2-acetamidoacrylic acid, crotonamide, and dimethylcrotonamide.

[0011] Furthermore, compared with the solvent of the electrolyte, the functional additive has a high solvation energy with sodium ions, and is more easily combined with sodium ions in the electrolyte of the sodium ion battery. It adheres to the surface of the negative electrode during charging and discharging, and then undergoes a self-polymerization reaction under the catalytic action of the negative electrode active substance to form a protective film.

[0012] Furthermore, the functional additive is used to adhere to the surface of the negative electrode when the sodium ion battery is activated, undergo a self-polymerization reaction under the catalysis of potassium titanyl phosphate, and form a protective layer on the surface of potassium titanyl phosphate.

[0013] Furthermore, the steps of activating the sodium ion battery are:

[0014] S1, charge to 50% SOC with 2-5C rate current;

[0015] S2, continue charging to 80% SOC with a current rate of 0.1-0.5C, and charge at a constant voltage for 1-5h;

[0016] S3, continue charging to 100% SOC using 1-2C rate current;

[0017] S4, discharge at a rate of 1C to the discharge cut-off voltage.

[0018] In step S1, a large current is used to increase the voltage difference between the positive and negative electrodes, so that the functional additives can be quickly migrated to the surface of the negative electrode under the voltage difference between the positive and negative electrodes; in step S2, a small current is used to reduce the voltage difference between the positive and negative electrodes, so as to ensure that the functional additives migrated to the vicinity of the negative electrode can be stably attached to the surface of the negative electrode, and fully self-polymerize during the constant voltage charging process to form a protective layer on the surface of the negative electrode active material; in steps S3 and S4, charging and discharging are carried out according to the conventional formation procedure to save time and improve efficiency.

[0019] Furthermore, the sodium ion battery activation is carried out at a temperature of 35-55°C.

[0020] Furthermore, the functional additive quickly migrates to the negative electrode surface at S1, adheres to the negative electrode surface at S2 and undergoes a self-polymerization reaction under the catalysis of potassium titanyl phosphate, forming a protective layer on the surface of potassium titanyl phosphate.

[0021] Furthermore, the polyanion material is sodium ferric pyrophosphate, with a molecular formula of Na x Fe y (PO4)2(P2O7), wherein x=3-4, y=2-3, preferably x=4, y=3.

[0022] Furthermore, the electrolyte of the electrolyte is a sodium salt, preferably sodium hexafluorophosphate; and the solvent is a carbonate solvent, preferably polycarbonate.

[0023] Beneficial effects of the present invention:

[0024] The present invention adds a functional additive to the electrolyte of the sodium ion battery, which migrates to the surface of the negative electrode during the charging process. Under the catalysis of the negative electrode KTiOPO4 active substance, a self-polymerization reaction occurs to form an effective protective layer, which successfully blocks the direct contact between the electrolyte and the negative electrode active substance, and fundamentally inhibits the catalytic decomposition of the electrolyte by Ti ions in the negative electrode active substance KTiOPO4, thereby specifically solving the problem of gas production by the decomposition of the electrolyte catalyzed by Ti ions.

[0025] The present invention adopts a step-by-step activation system. First, a large current is used for charging to facilitate the rapid migration of functional additives to the negative electrode. Then a small current is used to make the functional additives stably adhere to the surface of the negative electrode to undergo a self-polymerization reaction to form an effective protective film, thereby effectively isolating the negative electrode KTiOPO4 from the electrolyte.

[0026] The invention is easy to operate, low in cost, and has significant effects and long-lasting stability; it effectively improves the cycle stability of the sodium ion battery, prolongs the service life of the battery, and provides strong technical support for the wide application of the negative electrode KTiOPO4 in the battery field. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The embodiment of the present invention provides a sodium ion battery based on a titanium-based phosphate negative electrode, comprising a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, wherein the positive electrode comprises a polyanion material having a sodium superion conductor structure, the negative electrode comprises potassium titanyl phosphate, and the functional additive contained in the electrolyte has a general structural formula of: Wherein, the R1, R2, and R3 are independently selected from one of halogen atoms, oxygen atoms, hydroxyl groups, amino groups, and C1-C10 alkyl groups. In this embodiment, the sodium ion battery uses titanium-based phosphate KTiOPO4 as the negative electrode active material, and adds functional additives in the electrolyte. The functional additives have carbon-carbon double bonds and carbonyl groups adjacent to carbon-carbon double bonds. The functional additives migrate to the negative electrode surface during charging, and self-polymerize under the catalysis of the negative electrode KTiOPO4, forming a protective layer on the surface of KTiOPO4, avoiding contact between KTiOPO4 and the electrolyte, thereby preventing the negative electrode Ti ions from catalytically decomposing the electrolyte, improving the cycle stability of the battery, and extending the battery life. The present invention only needs to add specific functional additives to the electrolyte, which is simple to operate, low in cost, and has significant effects and long-lasting stability. It effectively improves the cycle stability of the sodium ion battery, extends the battery life, and provides strong technical support for the wide application of the negative electrode KTiOPO4 in the battery field.

[0029] As an embodiment, the addition amount of the functional additive is 0.1%-2% of the mass of the electrolyte, such as 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, etc., including but not limited to this; the functional additive is used to adhere to the surface of the negative electrode when the sodium ion battery is activated, and undergo self-polymerization reaction under the catalysis of potassium titanyl phosphate to form a protective layer on the surface of potassium titanyl phosphate; compared with the solvent of the electrolyte, the functional additive has a high solvation energy with sodium ions, and is more easily combined with sodium ions in the electrolyte of the sodium ion battery. It adheres to the surface of the negative electrode with charging and discharging, and then undergoes self-polymerization reaction under the catalytic action of the negative electrode active substance to form a protective film; as a specific example, the functional additive is selected from one or more of acrylamide, tetrahydrofurfuryl methacrylate, 2-acetamidoacrylic acid, crotonamide, and dimethylcrotonamide.

[0030] As an implementation method, the steps of activating the sodium ion battery are as follows: S1, charging to 50% SOC with a 2-5C current rate; S2, continuing to charge to 80% SOC with a 0.1-0.5C current rate, and charging at a constant voltage for 1-5h; S3, continuing to charge to 100% SOC with a 1-2C current rate; S4, discharging to the discharge cut-off voltage with a 1C current rate. In step S1, a large current is used to increase the voltage difference between the positive and negative electrodes, so that the functional additives can be quickly migrated to the negative electrode surface under the voltage difference between the positive and negative electrodes; in step S2, a small current is used to reduce the voltage difference between the positive and negative electrodes, so as to ensure that the functional additives migrated to the vicinity of the negative electrode can be stably attached to the negative electrode surface, and fully undergo self-polymerization reaction during the constant voltage charging process to form a protective layer on the surface of the negative electrode active material; in steps S3 and S4, charging and discharging are performed according to the conventional formation procedure to save time and improve efficiency.

[0031] As an embodiment, the sodium ion battery activation is carried out at a temperature of 35-55°C; the functional additive quickly migrates to the surface of the negative electrode at S1, adheres to the surface of the negative electrode at S2 and undergoes a self-polymerization reaction under the catalysis of potassium titanyl phosphate, forming a protective layer on the surface of potassium titanyl phosphate.

[0032] As an embodiment, the polyanion material is sodium ferric pyrophosphate, with a molecular formula of Na x Fe y (PO4)2(P2O7), wherein x=3-4, y=2-3, preferably x=4, y=3.

[0033] As an embodiment, the electrolyte of the electrolyte solution is a sodium salt, preferably sodium hexafluorophosphate; the solvent is a carbonate solvent, preferably polycarbonate.

[0034] The following are specific embodiments.

[0035] Example 1

[0036] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode, and the preparation method comprises the following steps:

[0037] (1) Sodium phosphate iron pyrophosphate Na4Fe3(PO4)2(P2O7) and potassium titanyl phosphate KTiOPO4 were used as positive and negative active materials to prepare positive and negative electrode sheets, respectively. A mixed slurry of 80% active material, 10% super P (super carbon black) and 10% polyvinylidene fluoride was coated on aluminum foil by mass percentage. After drying at 100°C for 10 hours, the electrode film was punched into a sheet with a diameter of 14 mm. The mass load of the positive and negative electrode sheets was approximately 2.5 mg / cm 2 and 2.0mg / cm 2 .

[0038] (2) In a glove box filled with argon, a sodium ion battery was assembled using a 9 μm thick PE separator, a positive electrode sheet, a negative electrode sheet and an electrolyte. The electrolyte used PC as a solvent and sodium hexafluorophosphate as an electrolyte, and a functional additive was added. The functional additive was acrylamide, and the addition amount was 1% of the electrolyte mass.

[0039] (3) Battery activation: using a 3C current rate to charge to 50% SOC; using a 0.2C current rate to continue charging to 80% SOC, constant voltage charging for 3 hours; using a 2C current rate to continue charging to 100% SOC; using a 1C current rate to discharge to the discharge cut-off voltage, to obtain a sodium ion battery.

[0040] Example 2

[0041] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode. The difference from Embodiment 1 is that tetrahydrofurfuryl methacrylate is used as a functional additive of the electrolyte, and other steps and parameters remain unchanged.

[0042] Example 3

[0043] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode. The difference from Embodiment 1 is that 2-acetamidoacrylic acid is used as a functional additive of the electrolyte, and other steps and parameters remain unchanged.

[0044] Example 4

[0045] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode. The difference from Embodiment 1 is that the addition amount of the functional additive of the electrolyte is adjusted to 0.2%, and the other steps and parameters remain unchanged.

[0046] Example 5

[0047] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode. The difference from Embodiment 1 is that the addition amount of the functional additive of the electrolyte is adjusted to 2%, and the other steps and parameters remain unchanged.

[0048] Example 6

[0049] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode. The difference from Embodiment 1 is that a 2C rate current is used to charge to 50% SOC, and other steps and parameters remain unchanged.

[0050] Example 7

[0051] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode. The difference from Embodiment 1 is that a 5C rate current is used to charge to 50% SOC, and other steps and parameters remain unchanged.

[0052] Example 8

[0053] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which is different from Embodiment 1 in that after charging to 80% SOC, constant voltage charging is performed for 1 hour, and other steps and parameters remain unchanged.

[0054] Example 9

[0055] This embodiment relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which is different from Embodiment 1 in that after charging to 80% SOC, constant voltage charging is performed for 5 hours, and other steps and parameters remain unchanged.

[0056] Comparative Example 1

[0057] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which is different from Example 1 in that fluoroethylene carbonate is used as a functional additive of the electrolyte, and other steps and parameters remain unchanged.

[0058] Comparative Example 2

[0059] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which differs from Example 1 in that no functional additives are added to the electrolyte, and other steps and parameters remain unchanged.

[0060] Comparative Example 3

[0061] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which differs from Example 1 in that the addition amount of the functional additive of the electrolyte is adjusted to 4%, and other steps and parameters remain unchanged.

[0062] Comparative Example 4

[0063] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which differs from Example 1 in that a 1C rate current is used to charge the battery to 50% SOC, and other steps and parameters remain unchanged.

[0064] Comparative Example 5

[0065] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which differs from Example 1 in that a 10C rate current is used to charge the battery to 50% SOC, and other steps and parameters remain unchanged.

[0066] Comparative Example 6

[0067] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which is different from Example 1 in that after charging to 80% SOC, constant voltage charging is performed for 0.5 h, and other steps and parameters remain unchanged.

[0068] Comparative Example 7

[0069] This comparative example relates to a sodium ion battery based on a titanium-based phosphate negative electrode, which differs from Example 1 in that after charging to 80% SOC, constant voltage charging is performed for 8 hours, and other steps and parameters remain unchanged.

[0070] Test Case

[0071] (1) Rate performance test: The sodium ion batteries prepared in Examples 1-9 and Comparative Examples 1-7 were charged and discharged 5 times at rates of 1C, 5C, 10C, and 20C, respectively, and then the specific capacity of the sodium ion batteries after 5 cycles of charge and discharge at different rates was recorded (positive electrode in excess, calculated based on the negative electrode).

[0072] (2) Cycle stability test: The sodium ion batteries prepared in Examples 1-9 and Comparative Examples 1-7 were subjected to a 5C charge and 5C discharge cycle test at room temperature on a battery cycle test device with a discharge voltage range of 0.5 V to 3 V. The capacity of the first cycle was recorded as Q initial, and the capacity after 5000 cycles was recorded as Q5000 cycles. The capacity retention rate of each battery after 5000 cycles was calculated as (Q5000 cycles / Q initial) × 100%.

[0073] The rate performance test and cycle performance test results of the sodium ion batteries prepared in Examples 1-9 and Comparative Examples 1-7 are shown in Table 1.

[0074] Table 1

[0075]

[0076] As can be seen from Table 1, the sodium ion batteries of Examples 1-9 maintain excellent specific capacities after 5 cycles of charge and discharge at rates of 1C, 5C, 10C, and 20C. At the same time, they all have high capacity retention rates after 5000 cycles of charge and discharge, especially the sodium ion battery of Example 1 has a capacity retention rate of up to 95.8% after 5000 cycles.

[0077] From the comparison between Examples 1-3 and Comparative Example 1, it can be seen that Examples 1-3 use functional additives containing carbon-carbon double bonds and carbonyl groups adjacent to carbon. The functional additives have higher solvation energy with sodium ions in the electrolyte. Compared with PC solvents, they are more likely to adhere to the surface of the negative electrode during charging and discharging. Under the catalysis of the negative electrode active substance, self-polymerization occurs. The adjacent carbon of the carbon-carbon double bond is prone to breakage and polymerization in the presence of a carbonyl group, forming a protective layer on the surface of the negative electrode active substance to avoid contact between the electrolyte and the negative electrode active substance and improve the cycle stability. However, the functional additive in Comparative Example 1 cannot form an effective protective layer. Therefore, the cycle stability is relatively poor, and the capacity retention rate after 5000 cycles is only 35.7%.

[0078] From the comparison of Examples 1, 4-5 and Comparative Examples 2-3, it can be seen that when the addition amount of the functional additives in Examples 1 and 4-5 is between 0.1% and 2%, the rate performance and capacity retention rate of the battery are not much different; however, when no additive is added to Comparative Example 2, the capacity retention rate of 5000 cycles is only 21.5%, and when the addition content is 4%, the rate performance of the battery is lost because the protective film formed in the activation stage is relatively thick.

[0079] From the comparison of Examples 1, 6-7 and Comparative Examples 4-5, it can be seen that when the sodium ion battery is activated, when the sodium ion batteries of Examples 1 and 6-7 are charged at a rate of 2-5C in the first stage, the rate performance and capacity retention rate of the battery are not much different; however, when Comparative Example 4 is charged at 1C, although there is not enough pressure difference, the charging time is long enough, and the additives attached to the negative electrode are more than normal. For the same constant voltage charging time, some additives cannot be polymerized to form a protective film, which hinders the ion transmission, and the rate performance is slightly reduced. At the same time, the additives accumulated on the surface of the negative electrode produce side reactions, resulting in a decrease in cycle performance; when Comparative Example 5 is charged at a high rate of 10C, the polarization pressure difference of the battery is too large, the charging time is short, and when it reaches 50% SOC, the content of additive molecules on the surface of the negative electrode is not high, and the protective film formed is not tight enough. Although the rate performance is not much different, the cycle stability is sharply reduced.

[0080] From the comparison of Examples 1, 8-9 and Comparative Examples 6-7, it can be seen that when the sodium ion battery is activated, the rate performance and capacity retention rate of the sodium ion batteries in Examples 1 and 8-9 are not much different when the second stage constant voltage charging time is 1-5h. However, the constant voltage charging time of Comparative Example 6 is less than 1h, because the protective film formed is not tight enough, the rate performance is not much different, but the cycle stability is sharply reduced; the constant voltage charging time of Comparative Example 7 is 8h, because the protective film formed is too thick, although the cycle stability is good, the rate performance is seriously reduced.

[0081] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A sodium ion battery based on a titanium-based phosphate negative electrode, comprising a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode, characterized in that: The positive electrode includes a polyanion material having a sodium superion conductor structure, the negative electrode includes potassium titanyl phosphate, and the functional additive contained in the electrolyte has a general structural formula of: Wherein, R1, R2, and R3 are independently selected from one of a halogen atom, an oxygen atom, a hydroxyl group, an amino group, and a C1-C10 alkyl group.

2. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: The added amount of the functional additive is 0.1%-2% of the mass of the electrolyte.

3. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: The functional additive is selected from one or more of acrylamide, tetrahydrofurfuryl methacrylate, 2-acetamidoacrylic acid, butenamide, and dimethylbutenamide.

4. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: Compared with the solvent of the electrolyte, the solvation energy between the functional additive and the sodium ions is high.

5. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: The functional additive is used to adhere to the surface of the negative electrode when the sodium ion battery is activated, and undergoes a self-polymerization reaction under the catalysis of potassium titanyl phosphate to form a protective layer on the surface of the potassium titanyl phosphate.

6. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: The steps of activating the sodium ion battery are: S1, charge to 50% SOC with 2-5C rate current; S2, continue charging to 80% SOC with a current rate of 0.1-0.5C, and charge at a constant voltage for 1-5h; S3, continue charging to 100% SOC using 1-2C rate current; S4, discharge at a rate of 1C to the discharge cut-off voltage.

7. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 6, characterized in that: The sodium ion battery activation is carried out at a temperature of 35-55°C.

8. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 6, characterized in that: The functional additive quickly migrates to the negative electrode surface in S1, adheres to the negative electrode surface in S2 and undergoes a self-polymerization reaction under the catalysis of potassium titanyl phosphate to form a protective layer on the surface of potassium titanyl phosphate.

9. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: The polyanion material is sodium ferric phosphate pyrophosphate, with a molecular formula of Na x Fe y (PO4)2(P2O7), where x=3-4, y=2-3.

10. The sodium ion battery based on titanium-based phosphate negative electrode according to claim 1, characterized in that: The electrolyte of the electrolyte is sodium salt, and the solvent is a carbonate solvent.

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