A Prussian blue sodium-ion battery and its preparation method

Abstract

A Prussian blue sodium-ion battery and its preparation method are disclosed, belonging to the field of sodium-ion battery technology. The specific solution is as follows: A Prussian blue sodium-ion battery includes a positive electrode and a negative electrode. The positive electrode includes a positive current collector and a positive active material layer on the surface of the current collector containing positive active material. The water content of the positive active material layer is 0-90 μg / g. Only a portion of the voltage plateau of the positive active material functions during battery charging and discharging. This invention fundamentally solves the problem of battery swelling and electrical performance degradation caused by water in the positive active material. Furthermore, by controlling the insertion / extraction depth of sodium ions in the Prussian blue positive electrode material, the damage caused to the structure of the Prussian blue positive electrode material by deep insertion / extraction of sodium ions during battery charging and discharging is reduced, thereby achieving long-cycle performance of the sodium-ion battery while maintaining a high specific capacity of the Prussian blue positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a Prussian blue type sodium ion battery and a preparation method thereof. BACKGROUND

[0002] In electrochemical energy storage, the development of lithium ion batteries in the energy storage market is limited due to resource bottlenecks. Since electrochemical energy storage technology does not require batteries to have extremely high energy density, but rather focuses on the high safety and long service life of batteries, energy density is slightly lower but resource-abundant sodium ion batteries have once again attracted the attention of researchers. Sodium ion batteries have the advantages of high safety, good rate performance and excellent low-temperature performance, and are currently considered to be the most promising form of electrochemical energy storage. Among them, Prussian blue type materials are one of the important directions for the development of sodium ion battery cathode materials.

[0003] Currently, the mainstream preparation method of sodium Prussian blue type materials for sodium ion battery cathode materials is still chemical co-precipitation. This method has the advantages of low cost and simple process. However, the sodium Prussian blue type material prepared by chemical co-precipitation generally contains a large amount (about 10%) of crystal water (including coordination water and interstitial water). The presence of crystal water, on the one hand, will reduce the electrochemical activity of the cathode material, thereby affecting the specific capacity of the cathode material; on the other hand, during the electrochemical reaction of the battery, the crystal water will be electrolyzed, and the crystal water is prone to side reactions with the electrolyte, thereby causing the battery to swell and the cycle performance to decrease.

[0004] In addition, after the sodium Prussian blue type material is baked to remove the crystal water, its specific capacity will be significantly improved, but its stability will decrease sharply and its cycle performance will be poor. This is because the coordination water contained in the Prussian blue type material plays an important role in supporting its crystal structure. Once the coordination water in the crystal structure of the Prussian blue type material is removed, the crystal structure of the Prussian blue type material may collapse during the sodium ion deintercalation process, resulting in a decrease in active sites for sodium ion intercalation and deintercalation, thereby affecting the capacity and cycle performance of the sodium ion battery.

[0005] The positive plate and preparation method thereof and the sodium ion battery disclosed by Chinese invention patent CN 109728252A control the water content of the Prussian blue material to be 100-5000 mu g / g, so as to reduce the probability of side reaction of the coordination water and the electrolyte, so that the sodium ion battery does not have serious outgassing during the charging and discharging process, and can be normally charged and discharged. However, this cannot fundamentally prevent the crystallization water from being electrolyzed and the crystallization water from reacting with the electrolyte, thereby causing the battery to outgas and the electrical performance to deteriorate; it is also difficult to ensure that the coordination water will not be removed during the water removal process, causing the crystal structure of the Prussian blue material to partially collapse during the cycle process, thereby reducing the cycle performance of the sodium ion battery; at the same time, controlling the water content of the material to be moderate also increases the difficulty of process control to a certain extent. SUMMARY

[0006] The first object of the present application is to solve the problems existing in the prior art and provide a Prussian blue type sodium ion battery.

[0007] The second object of the present application is to provide a preparation method of the Prussian blue type sodium ion battery.

[0008] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0009] A Prussian blue type sodium ion battery comprises a positive plate and a negative plate, the positive plate comprises a positive current collector and a positive active material layer existing on the surface of the positive current collector and containing a positive active material, the water content of the positive active material layer is 0-90 mu g / g, and the positive active material only partially functions in the voltage platform during the charging and discharging process of the battery.

[0010] Further, by matching the capacity of the positive plate and the negative plate and controlling the upper limit voltage and the lower limit voltage of the battery during the charging and discharging process, the positive active material only partially functions in the voltage platform during the charging and discharging process of the battery.

[0011] Further, the formula for matching the capacity of the positive plate and the negative plate is: the capacity per unit area of the negative plate = the capacity per unit area of the positive plate*(50%-95%)*(1.0-1.5).

[0012] Further, the partial voltage platform functioning refers to 25%-95% of the capacity of the entire voltage platform functioning.

[0013] Further, the positive active material is a Prussian blue material, and the molecular formula of the Prussian blue material is Na x M a [M b (CN)6], wherein M a is a transition metal, M bM is a transition metal, 0 < x ≤ 2 a M is selected from one of Fe, Co, Mn, Cu, Zn, Cr, V b M is selected from one of Fe, Co, Mn, Cu, Zn, Cr, V.

[0014] Further, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer existing on the surface of the negative electrode current collector and containing a negative electrode active material, and the water content of the negative electrode active material layer is 0 μg / g to 200 μg / g.

[0015] Further, the Prussian blue type sodium ion battery further comprises a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, and the water content of the separator is 0 μg / g to 200 μg / g.

[0016] A preparation method of the Prussian blue type sodium ion battery comprises the following steps:

[0017] Step one, manufacturing a positive electrode sheet and a negative electrode sheet, and then performing vacuum drying treatment on the positive electrode sheet and the negative electrode sheet, so that the water content of the positive electrode active material layer in the positive electrode sheet is controlled to be 0 μg / g to 90 μg / g.

[0018] Step two, completing the lamination or winding process, the assembly process, the liquid injection process and the packaging process of the battery in an environment with a dew point less than -45℃.

[0019] Further, the upper limit voltage and the lower limit voltage of the battery are determined according to the capacity per unit area of the negative electrode sheet of the battery, the capacity per unit area of the positive electrode sheet, and the region in which the voltage platform of the positive electrode active material functions when the battery is formed and used.

[0020] The beneficial effects of the present application relative to the prior art are:

[0021] The Prussian blue type sodium ion battery of the present application, the positive electrode active material is a Prussian blue type material, and the water content of the positive electrode active material layer is 0 μg / g to 90 μg / g, which not only eliminates the water in the positive electrode active material from being electrolyzed in the charging and discharging process, but also eliminates the side reaction of the water in the positive electrode active material with the electrolyte, thereby fundamentally solving the problem of gas swelling and performance deterioration of the battery caused by the water in the positive electrode active material. In addition, by controlling the depth of sodium ion deintercalation in the Prussian blue type positive electrode material, the damage to the structure of the Prussian blue type positive electrode material caused by the deep deintercalation of sodium ion in the battery charging and discharging process is weakened, thereby realizing the long cycle performance of the sodium ion battery while maintaining the high gram capacity of the Prussian blue type positive electrode material.

[0022] The Prussian blue type sodium ion battery in the present application has a simple manufacturing process, key factors are easy to control, and is convenient for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The first charge-discharge voltage-specific capacity curve of the battery prepared in Example 1;

[0024] Figure 2 The voltage-specific capacity curve of the battery prepared in Example 1 during the second charge-discharge cycle is shown.

[0025] Figure 3 A comparison graph showing the capacity retention rate curves of the batteries prepared in Example 1 and Comparative Example 1;

[0026] Figure 4 The voltage-specific capacity curve of the battery prepared in Comparative Example 1 during the first charge-discharge cycle;

[0027] Figure 5 The first charge-discharge voltage-specific capacity curve of the battery prepared in Example 3;

[0028] Figure 6 A comparison graph showing the capacity retention rate curves of the batteries prepared in Example 3 and Comparative Example 3;

[0029] Figure 7 The first charge-discharge voltage-specific capacity curve of the battery prepared in Comparative Example 3; Detailed Implementation

[0030] The following is in conjunction with the appendix Figures 1-7 The present invention will be described in detail with reference to specific embodiments. Specific Implementation Method 1

[0032] A Prussian blue sodium-ion battery includes a positive electrode, a negative electrode, an electrolyte, a separator, and a packaging shell. The positive electrode includes a positive current collector and a positive active material layer on the surface of the positive current collector containing positive active material. The water content of the positive active material layer is 0-90 μg / g. By matching the capacity of the positive and negative electrodes and controlling the upper and lower voltage limits of the battery during charging and discharging, the positive active material is made to function only at part of the voltage plateau during the charging and discharging process.

[0033] Furthermore, the formula for capacity matching between the positive and negative electrodes is: Capacity per unit area of ​​the negative electrode = Capacity per unit area of ​​the positive electrode * (50% ~ 95%) * (1.0 ~ 1.5).

[0034] Furthermore, "partial voltage platform utilization" means that at least 25% of the total voltage platform capacity can be utilized, and at most 95% of the total voltage platform capacity can be utilized.

[0035] Furthermore, the positive electrode active material is a Prussian blue-based material, and the molecular formula of the Prussian blue-based material is Na.x M a [M b (CN)6], where M a M is a transition metal. b It is a transition metal, 0 <x≤2,M a Selected from one of Fe, Co, Mn, Cu, Zn, Cr, and V, M b It is selected from one of Fe, Co, Mn, Cu, Zn, Cr, and V.

[0036] Furthermore, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer on the surface of the negative electrode current collector containing negative electrode active material, wherein the water content of the negative electrode active material layer is 0-200 μg / g, preferably 0-100 μg / g.

[0037] Furthermore, the negative electrode active material is a conventional negative electrode active material used in sodium-ion batteries, referring to a material with sodium storage function and a standard electrode potential lower than that of Prussian blue materials, including but not limited to at least one of metallic sodium, sodium alloys, and carbon-based materials. Preferably, the negative electrode active material is elemental sodium, SnSb / C, Na2Ti3O7, hard carbon, or soft carbon.

[0038] Furthermore, the electrolyte includes an organic solvent, a sodium salt dissolved in the organic solvent, additives, etc., and the specific composition and ratio are the same as those of a conventional sodium-ion battery, with no special requirements; the sodium salt includes sodium perchlorate or sodium hexafluorophosphate.

[0039] Furthermore, the Prussian blue sodium-ion battery also includes a separator located between the positive and negative electrode plates, wherein the water content of the separator is 0–200 μg / g, preferably 0–100 μg / g.

[0040] In this invention, the water content of the positive electrode active material layer is between 0 μg / g and 90 μg / g. At this point, the water content of the positive electrode active material is extremely low, which not only prevents the water in the positive electrode material from being electrolyzed during charging and discharging, but also prevents the water in the positive electrode material from undergoing side reactions with the electrolyte. This fundamentally solves the problem of water in the positive electrode material causing battery swelling and deterioration of electrical performance.

[0041] In addition, the Prussian blue type positive electrode material has the best ability to deintercalate sodium ions when the water content is extremely low, but the stability is poor. If the Prussian blue type positive electrode material is directly used without control, the crystal structure of the Prussian blue type material will collapse due to the deep deintercalation of sodium ions during the charging and discharging process, resulting in capacity attenuation and poor cycle performance of the battery. The Prussian blue type sodium ion battery provided by the application controls the deintercalation depth of sodium ions in the Prussian blue type positive electrode material, so as to weaken the damage to the structure of the Prussian blue type positive electrode material caused by the deintercalation of sodium ions during the charging and discharging process of the battery, thereby realizing long cycle performance of the sodium ion battery while maintaining high specific capacity of the Prussian blue type positive electrode material. Specific embodiment two

[0043] A preparation method of the Prussian blue type sodium ion battery described in a specific embodiment one, comprising the following steps:

[0044] Step one, manufacturing a positive electrode sheet and a negative electrode sheet, and then performing vacuum drying treatment on the positive electrode sheet, the negative electrode sheet and a separator, so that the water content of the positive electrode active material in the positive electrode sheet is controlled to be 0-90 μg / g, the water content of the negative electrode active material in the negative electrode sheet is controlled to be 0-200 μg / g, and the water content of the separator is controlled to be 0-200 μg / g, wherein the method of manufacturing the positive electrode sheet and the negative electrode sheet is the same as that of a conventional sodium ion battery and has no special requirement;

[0045] Step two, completing the lamination or winding process, the assembly process, the liquid injection process and the packaging process of the battery in a dry room environment with a dew point less than-45℃; the specific process is the same as that of a conventional sodium ion battery and has no special requirement.

[0046] Further, the upper limit voltage and the lower limit voltage of the battery are determined according to the capacity per unit area of the negative electrode sheet, the capacity per unit area of the positive electrode sheet and the region in which the voltage platform of the positive electrode active material works when the battery is formed and used.

[0047] Further, the water content of the positive electrode active material layer is tested by using a Karl Fischer moisture tester, and the test temperature is 170℃ and the test environment is a dry room with a dew point less than-45℃.

[0048] Example 1

[0049] In this embodiment, the Prussian blue type material Na2Fe[Fe(CN)6] is selected as the positive electrode material of the sodium ion battery to manufacture a positive electrode sheet, and then the positive electrode sheet is vacuum dried, and finally the water content of the positive electrode active material layer is measured to be 90 μg / g.

[0050] The sodium sheet is rolled on an aluminum foil. Since the water content of sodium is far lower than 100 μg / g, the negative electrode sheet is obtained by directly die cutting without vacuum drying.

[0051] The above negative electrode sheet, positive electrode sheet and separator (glass fiber separator) were stacked to form an electrode, which was then put into a packaging shell, and then subjected to liquid injection (using NaPF6 electrolyte), infiltration, packaging and other processes to obtain a Prussian blue type sodium ion battery. Then the prepared sodium ion battery was subjected to formation and cycle test, wherein the voltage platform of the Prussian blue type material Na2Fe[Fe(CN)6] accounted for 50% of the entire discharge voltage platform capacity.

[0052] Comparative Example 1

[0053] The preparation process of the Prussian blue type sodium ion battery of Comparative Example 1 was the same as that of Example 1, except that

[0054] The obtained sodium ion battery was subjected to formation and cycle test, wherein the voltage platform of the Prussian blue type material Na2Fe[Fe(CN)6] accounted for 100% of the entire voltage platform capacity.

[0055] The first cycle charge-discharge voltage-specific capacity curve of the battery prepared in Example 1 is shown in Figure 1 , the second cycle charge-discharge voltage-specific capacity curve is shown in Figure 2 , and the charge-discharge voltage-specific capacity curve after the second cycle is similar to that of the second cycle; the first cycle charge-discharge voltage-specific capacity curve of the battery obtained in Comparative Example 1 is shown in Figure 4 , and the charge-discharge voltage-specific capacity curve after the first cycle is similar to that of the first cycle. The capacity retention rate curve of the battery obtained in Comparative Example 1 is shown in Figure 3 . It can be seen that the capacity retention rate of the Prussian blue type sodium ion battery obtained in Example 1 is 88.79% after 1000 cycles, which is much higher than that of the conventional Prussian blue type sodium ion battery obtained when the entire voltage platform of the Prussian blue type material Na2Fe[Fe(CN)6] is fully utilized (the capacity retention rate is 80% after 37 cycles).

[0056] When the water content in the positive electrode active material layer is low (0 μg / g to 90 μg / g), although the initial capacity of the sodium-ion battery is high, if the entire sodium storage capacity of the positive electrode active material is utilized without control, the cycle performance of the sodium-ion battery will be very poor, rendering it unusable, as shown in Comparative Example 1. This is because when the water content in the positive electrode active material layer is low, the coordinated water in the Prussian blue-like material crystal structure has already been extracted. Repeated deep intercalation and deintercalation of sodium will cause the material's crystal structure to collapse, resulting in the Prussian blue-like material partially losing its sodium storage capacity, thus leading to poor cycle performance of the sodium-ion battery. In Example 1, by controlling the proportion of the capacity utilized by the entire discharge voltage plateau, the depth of sodium ion intercalation and deintercalation in the Prussian blue-like positive electrode material is controlled, thereby reducing the damage caused by deep sodium ion intercalation and deintercalation to the Prussian blue-like positive electrode material structure during battery charging and discharging. This allows for better cycle performance of the sodium-ion battery while maintaining a high specific capacity of the Prussian blue-like positive electrode material.

[0057] Example 2

[0058] The preparation process of the Prussian blue sodium-ion battery in this embodiment is the same as that in Example 1, the difference being...

[0059] Preparation of negative electrode sheet: Hard carbon was made into negative electrode sheet, and then the negative electrode sheet was vacuum dried. Finally, the water content of the negative electrode active material layer was measured to be 100 μg / g.

[0060] Preparation of the positive electrode: The water content of the positive electrode active material layer is 50 μg / g. (See attached image) Figure 4 As shown, at this time, the Prussian blue material Na2Fe[Fe(CN)6] itself has a good ability to intercalate and deintercalate sodium ions, and the specific capacity of the material can reach 150mAh / g. In this embodiment, by controlling the voltage window, the voltage platform at which the Prussian blue material Na2Fe[Fe(CN)6] can play a role is the first 45% of the capacity of the entire discharge voltage platform, that is, the actual specific capacity of the cathode material is 67.5mAh / g.

[0061] The diaphragm used is a conventional polypropylene (PP) membrane.

[0062] Comparative Example 2

[0063] Comparative Example 2: The preparation process of the Prussian blue sodium-ion battery was the same as that of Example 2. The difference was that the obtained sodium-ion battery underwent formation and cycle testing. In this test, the voltage plateau of the Prussian blue material Na2Fe[Fe(CN)6] accounted for 100% of the total voltage plateau capacity.

[0064] The Prussian blue sodium-ion battery prepared in Example 2 retains more than 99% of its capacity after 500 cycles, which is much higher than the cycle retention rate of the conventional Prussian blue sodium-ion battery obtained when the entire voltage plateau of the Prussian blue material Na2Fe[Fe(CN)6] in Comparative Example 2 is fully utilized (capacity retention rate of 80% after 35 cycles).

[0065] Example 3

[0066] The preparation process of the Prussian blue sodium-ion battery in this embodiment is the same as that in Example 2, the difference being...

[0067] Preparation of the positive electrode: The water content of the positive electrode active material layer is 20 μg / g. (See attached image) Figure 4 As shown, at this time, the Prussian blue material Na2Fe[Fe(CN)6] itself has a good ability to intercalate and deintercalate sodium ions, and the material specific capacity can reach 150mAh / g; in this embodiment, by controlling the voltage window, the voltage platform at which the Prussian blue material Na2Fe[Fe(CN)6] can play a role is the first 53% of the capacity of the entire charging voltage platform, that is, the actual material specific capacity of the cathode material is 80mAh / g.

[0068] Comparative Example 3

[0069] The preparation process of this comparative Prussian blue sodium-ion battery is the same as that in Example 2, except that...

[0070] Preparation of the positive electrode: The water content of the positive electrode active material layer is 100,000 μg / g. Because the water of crystallization occupies the sodium storage sites of the Prussian blue-based material Na2Fe[Fe(CN)6], the actual sodium storage capacity of the material is reduced. At this point, the specific capacity of the Prussian blue-based material Na2Fe[Fe(CN)6] is 80 mAh / g. In this comparative example, the voltage plateau where the positive electrode active material Prussian blue-based material Na2Fe[Fe(CN)6] functions is 100% of the total charging voltage plateau capacity, meaning the actual specific capacity of the positive electrode material is 80 mAh / g.

[0071] The charge / discharge voltage-specific capacity curve of the battery obtained in Example 3 is shown below. Figure 5 As shown, the charge / discharge voltage-specific capacity curves after the first cycle are similar in shape to those of the first cycle; the charge / discharge voltage-specific capacity curve of the battery obtained in Comparative Example 1 for the first cycle is as follows. Figure 7 As shown, the charge / discharge voltage-specific capacity curve of the obtained battery after the first cycle is similar in shape to that of the first cycle; the comparison chart of the capacity retention rate curve of the battery obtained in Example 3 and the capacity retention rate curve of the battery obtained in Comparative Example 3 is shown in Figure 3. Figure 6It can be seen that the sodium-ion battery of Prussian blue type obtained in Example 3 has a capacity retention rate of 98.19% after 70 cycles, which is much higher than that of the conventional sodium-ion battery of Prussian blue type (the capacity retention rate is 81.87% after 70 cycles) obtained when the Prussian blue type material Na2Fe[Fe(CN)6] has a high water content and the entire voltage platform is fully utilized.

[0072] When the water content of the positive active material layer is at a high level, on the one hand, the sodium storage sites of the Prussian blue type material Na2Fe[Fe(CN)6] are occupied by the crystal water, which reduces the real sodium storage capacity of the material; on the other hand, the water in the positive active material is electrolyzed during the charging and discharging process, and also reacts with the electrolyte, which leads to poor cycle performance and battery swelling, which is the case in Comparative Example 3. In Example 3, on the one hand, the water content of the positive active material layer is 20 μg / g, which not only prevents the water in the positive active material from being electrolyzed during the charging and discharging process, but also prevents the water in the positive active material from reacting with the electrolyte, thereby fundamentally solving the problem of battery swelling and performance deterioration caused by water in the positive active material; on the other hand, by controlling the proportion of the entire discharge voltage platform capacity to be utilized, the depth of sodium ion deintercalation in the Prussian blue type positive active material is controlled, thereby reducing the damage to the structure of the Prussian blue type positive active material caused by the deep deintercalation of sodium ions during the charging and discharging process of the battery, and thus realizing good cycle performance of the sodium-ion battery while maintaining a high specific capacity of the Prussian blue type positive active material.

[0073] The preferred embodiments of the present application have been described above with reference to the drawings, but the present application is not limited to the above examples, and various modifications and changes can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for using a Prussian blue-based sodium-ion battery, the Prussian blue-based sodium-ion battery comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer present on a surface of the positive electrode current collector and containing a positive electrode active material, characterized by: The water content of the positive electrode active material layer is 0 μg / g to 90 μg / g, the capacity of the positive electrode sheet is matched with the capacity of the negative electrode sheet, and the upper limit voltage and the lower limit voltage of the battery during charging and discharging are controlled, so that the positive electrode active material only partially exerts the voltage platform during charging and discharging of the battery.

2. The method of using a Prussian blue-based sodium-ion battery of claim 1, wherein: The formula for matching the capacity of the positive electrode sheet and the negative electrode sheet is: the capacity per unit area of the negative electrode sheet = the capacity per unit area of the positive electrode sheet (50%~95%) (1.0~1.5).

3. The method of using a Prussian blue-based sodium-ion battery of claim 1, wherein: The partial voltage platform refers to 25% to 95% of the capacity of the entire voltage platform.

4. The method of using a Prussian blue-based sodium-ion battery of claim 1, wherein: The positive electrode active material is a Prussian blue type material, and the molecular formula of the Prussian blue type material is Na x M a [M b (CN)6], wherein M a is a transition metal, M b is a transition metal, 0 < x < 2, M a is selected from one of Fe, Co, Mn, Cu, Zn, Cr, V, M b is selected from one of Fe, Co, Mn, Cu, Zn, Cr, V.

5. The method of using a Prussian blue-based sodium-ion battery of claim 1, wherein: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer present on the surface of the negative electrode current collector and containing a negative electrode active material, and the water content of the negative electrode active material layer is 0 μg / g to 200 μg / g.

6. The method of using a Prussian blue-based sodium-ion battery of claim 1, wherein: The Prussian blue type sodium ion battery further comprises a separator, the separator is located between the positive electrode sheet and the negative electrode sheet, and the water content of the separator is 0 μg / g to 200 μg / g.

Images