Method and device for rapid in-situ monitoring of sodium precipitation at negative electrode side of soft-package sodium-ion battery

Abstract

The invention discloses a method and a device for rapid in-situ monitoring of sodium precipitation at a negative electrode side of a soft-package sodium-ion battery. According to the method, the on-line nondestructive monitoring of the negative electrode sodium precipitation is realized by monitoring the pressure change of the sodium ion battery cell in the charging and discharging process. A first-order differential curve and a second-order differential curve of the pressure of the battery cell are obtained and analyzed by measuring and recording the pressure curve of the battery cell in the charging process on line, and when the change rate of the pressure of the battery cell exceeds a set threshold value and the second-order differential curve of the pressure is always larger than 0 under the high SOC, the second-order differential curve can serve as an external indication signal for judging sodium precipitation of the negative electrode. According to the technical scheme, the occurrence of the sodium separation reaction of the negative electrode can be efficiently and sensitively detected without any modification or damage to the target sodium ion battery cell. The method provides a simple and effective lossless online monitoring means which is easy to integrate and popularize for effectively defining the safe use condition of the sodium ion battery cell and monitoring and predicting the healthy operation condition of the sodium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion batteries, and in particular to a method and a device for rapid in-situ monitoring of sodium ion deposition on the negative electrode side of a soft-pack sodium ion battery. Background Art

[0002] In recent years, sodium-ion battery technology has regained the favor of researchers due to its advantages such as abundant global sodium resources, low cost, and similar energy storage principles and process technologies as lithium-ion batteries, and has developed into an energy storage technology with great application potential. Amorphous carbon-based carbon materials have high reversible sodium storage capacity and are considered to be one of the most promising negative electrode materials for sodium-ion batteries. Amorphous carbon-based negative electrode materials have different microscopic pore structures, 0.1V vs. Na + / Na and below account for slightly different proportions of the theoretical sodium storage capacity, but are generally 50-70% or more. The low-potential sodium storage potential of this part of the amorphous carbon negative electrode is similar to the thermodynamic potential of metal sodium precipitation (0V vs.Na + / Na) is very close. Therefore, sodium-ion batteries are very likely to precipitate metallic sodium on the surface of the carbon negative electrode at low temperatures or during fast charging. The precipitated sodium metal has a high reactivity and may react with the electrolyte to cause the loss of active sodium in the sodium-ion battery, resulting in a decrease in battery capacity; at the same time, the sodium precipitation reaction will also induce continuous electrolyte decomposition, leading to side reactions such as increased battery impedance and electrolyte decomposition and gas production. The precipitated metallic sodium may also form sodium dendrites that pierce the diaphragm, causing safety hazards, which hinders the large-scale application of sodium-ion batteries. Therefore, a reasonable method is needed to prevent and predict the occurrence of sodium precipitation, and an efficient and sensitive sodium precipitation detection method is the basis for achieving all this.

[0003] At present, the general method for detecting sodium precipitation is disassembly detection, that is, disassembling the battery after cycling and detecting it with the naked eye or other physical characterization methods. This method is relatively complex and destructive, and has low detection efficiency for sodium precipitation, and it is difficult to promote it to the detection of sodium precipitation in large-scale mass production of sodium-ion batteries. The real-time monitoring method can detect sodium precipitation in time without damaging the battery, and has high detection efficiency.

[0004] The volume change of active materials in sodium-ion batteries is closely related to the sodium insertion mechanism and sodium insertion capacity. Conventional positive electrode materials have a low volume expansion coefficient, so the overall volume change of sodium-ion batteries mainly comes from the negative electrode material. During the charging process, sodium ions are extracted from the positive electrode and embedded in the hard carbon negative electrode, resulting in a change in the volume of the negative electrode, which is fed back to the change in the internal pressure of the battery. The sodium storage mechanism in the hard carbon negative electrode is very complex, including sodium adsorption at defect sites in the ramp voltage range, and pore filling and interlayer insertion in the platform voltage range, which is significantly different from the single lithium insertion mechanism of the graphite negative electrode of lithium-ion batteries. Therefore, the volume change of the hard carbon negative electrode in the sodium-ion battery is closely related to its unique sodium storage mechanism, and the sodium precipitation behavior of the hard carbon negative electrode of the sodium-ion battery cannot be reasonably judged and analyzed directly through the pressure monitoring model of the lithium-ion battery. Therefore, it is necessary to develop non-destructive online monitoring methods and technologies suitable for the negative electrode sodium precipitation process based on the specific chemical mechanism of sodium-ion batteries. Summary of the invention

[0005] The present invention mainly aims at the shortcomings of the existing sodium precipitation detection technology, and provides a method and device for rapid in-situ monitoring of sodium precipitation on the negative electrode side of soft-pack sodium ion batteries, which can efficiently and sensitively detect the occurrence of negative electrode sodium precipitation reaction without any modification or damage to the target sodium ion battery cell. This method provides a simple, effective, easy-to-integrate and popularize non-destructive online monitoring method for effectively defining the safe use conditions of sodium ion batteries and monitoring and predicting the healthy operation status of sodium ion batteries.

[0006] The above technical problems of the present invention are mainly solved by the following technical solutions: A method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery realizes in-situ non-destructive monitoring of sodium deposition on the negative electrode by monitoring the pressure change, first-order differential and second-order differential curves of the soft-pack sodium ion battery cell during the charge and discharge process.

[0007] The real-time pressure data of the soft-pack sodium-ion battery is obtained through a pressure testing device, and the method includes: using a pressure testing device, including an upper clamping plate and a lower clamping plate, placing the soft-pack sodium-ion battery cell to be tested between the two, and installing a pressure sensor and a force rod above the upper clamping plate. The force rod is used to apply pressure to the upper clamping plate to clamp the soft-pack sodium-ion battery cell to be tested between the upper and lower clamping plates, and the force rod can be locked by a locking nut. The pressure sensor is connected to a pressure online recording system.

[0008] In some embodiments, the cathode material of the sodium ion battery is one or a combination of commonly used cathode materials for sodium ion batteries such as layered oxide cathode, polyanion, Prussian blue, etc., preferably, a layered oxide material;

[0009] In some embodiments, the negative electrode material of the sodium ion battery is a carbon-based material, such as one or a combination of hard carbon, soft carbon, amorphous carbon, and graphite carbon, preferably a hard carbon material;

[0010] The method for quickly detecting whether a soft-pack sodium-ion battery has sodium precipitation comprises the following steps:

[0011] ①Put the soft-pack sodium-ion battery cell between the upper and lower clamps;

[0012] ② Rotate the force rod to make the upper and lower clamps clamp the battery cell, and according to the test requirements, make the pressure reach the required initial pressure value, and tighten the locking nut;

[0013] ③After the pressure value reaches a stable value, the target charge and discharge program is used for charging and discharging;

[0014] ④Online record the pressure value and change law of sodium ion battery cells under different charging and discharging conditions;

[0015] ⑤Analyze the quantitative relationship between the cell pressure and capacity, calculate the first-order differential curve and the second-order differential curve of the pressure changing with the cell capacity or voltage, and judge whether sodium precipitation is found in the negative electrode of the sodium-ion battery by whether the first-order differential curve under high SOC exceeds the pressure change rate threshold corresponding to the cell structure and whether the second-order differential curve is always greater than 0.

[0016] In some embodiments, the initial pressure that can be applied by the force-applying rod in step ② may be 0-500 kPa, preferably 50-200 kPa;

[0017] In some embodiments, in step ③, the sodium ion battery and the pressure detection device can be placed together in a constant temperature box and left to stand for more than 3 hours, preferably more than 8 hours.

[0018] In some embodiments, according to the measured pressure signal and capacity signal of the sodium ion battery cell, the first-order pressure differential curve and the second-order pressure differential curve corresponding to the sodium ion battery cell are determined, and it is judged whether the first-order pressure differential curve in the high SOC region exceeds the threshold value and whether the second-order differential curve is always greater than 0; if the first-order pressure differential curve exceeds the threshold value and the second-order differential curve is always greater than 0, it is used as an indicator for judging whether sodium precipitation has occurred in the sodium ion battery; if the first-order pressure differential curve does not exceed the threshold value and the second-order differential curve has a point less than 0, it is judged that no sodium precipitation has occurred in the sodium ion battery. The pressure change rate threshold can select the maximum value of the pressure-capacity first-order differential curve in the high SOC range at a rate of 0.1 to 1C for the battery cell.

[0019] In some embodiments, the high SOC is a SOC not less than 50%.

[0020] In some embodiments, determining a first-order differential curve and a second-order differential curve according to the pressure signal and the volume signal includes: Obtain a curve showing real-time changes in monitoring pressure versus cell capacity; The real-time pressure curve is smoothed and fitted to obtain the pressure-volume function; The first-order differential and the second-order differential of the pressure-volume function with respect to the volume are calculated to obtain the first-order differential curve and the second-order differential curve of pressure.

[0021] In some embodiments, the method for determining whether sodium precipitation occurs is as follows: if the first-order differential curve exceeds the pressure change rate threshold and the second-order differential curve is always greater than 0, it is determined that sodium precipitation has occurred in the sodium ion battery; if the first-order differential curve does not exceed the pressure change rate threshold and the second-order differential curve has a point less than 0, it is determined that sodium precipitation has not occurred in the sodium ion battery, and in other cases, no obvious sodium precipitation has occurred. The beneficial effects of the present invention are: The present invention measures and records the pressure curve of the sodium ion soft-pack battery cell during the conventional charge and discharge process online, and determines the sodium precipitation on the negative electrode side by obtaining and analyzing the first-order differential curve and the second-order differential curve of the battery cell pressure. This solution can be used alone as a technical means to detect sodium precipitation at the negative electrode of an in-situ single battery cell, and can also be used for sodium ion batteries in integrated battery stacks or modules. There is no need to perform any modification or destruction on the target sodium ion battery cell, and the occurrence and uniformity of sodium precipitation reaction at the carbon negative electrode of the sodium ion battery can be detected efficiently, sensitively and non-destructively. This method provides a simple, effective, easy-to-integrate and popularize non-destructive online monitoring means for effectively defining the safe use conditions of sodium ion batteries, and monitoring and predicting the healthy operation status of sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a pressure testing device for detecting the pressure of a sodium ion battery according to the present invention.

[0023] Figure 2 This is the SEM of HC after constant current charging in Example 1.

[0024] Figure 3 This is the SEM of HC after constant current charging in Example 2.

[0025] Figure 4 This is the SEM of HC after constant current charging in Example 3.

[0026] Figure 5 The charging curves, pressure curves, first-order pressure differential curves and second-order pressure differential curves of Example 1, Example 2 and Example 3 are shown. DETAILED DESCRIPTION

[0027] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0028] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0029] A device for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery cell in this embodiment is as follows: Figure 1 As shown, it includes an upper clamping plate 1 and a lower clamping plate 2, a sodium ion soft-pack battery cell 3 to be tested is arranged between the upper clamping plate 1 and the lower clamping plate 2, a pressure sensor 4 is installed above the upper clamping plate 1, and a force rod 5 and a locking nut 6 are arranged above the pressure sensor sheet 4. The locking nut 6 plays the role of locking the force rod to fix the distance between the upper and lower clamping plates, so that the measured pressure change can reflect the volume change during the battery charging process.

[0030] In some embodiments of the present invention, a method for rapidly detecting sodium precipitation in a soft-pack sodium ion battery using the above-mentioned device comprises the following steps:

[0031] ①Put the sodium ion soft-pack battery cell between the upper and lower clamps;

[0032] ② Rotate the force rod until the pressure reaches a certain value, and tighten the locking nut (the specific pressure value is the external pressure required for the actual operation of the battery cell to be tested);

[0033] ③After the pressure value reaches a stable value, the conventional constant current charging and discharging procedure is used for charging and discharging;

[0034] ④Online record the pressure value and change law of sodium ion battery cells under different charging and discharging conditions;

[0035] ⑤Analyze the quantitative relationship between the cell pressure value and the battery charge and discharge capacity, calculate the first-order differential curve and second-order differential curve of pressure changing with cell capacity or voltage, and determine whether sodium precipitation is found in the negative electrode of the sodium ion battery.

[0036] In order to clarify the detection principle of the embodiments of the present invention, the sodium analysis detection process of the sodium ion battery is described in detail by taking Embodiment 1, Embodiment 2 and Embodiment 3 as examples. The sodium ion batteries used in the embodiments have all undergone formation, and no gas is produced during the charging process, which will not affect the pressure test. The unit of voltage in the charging curve, pressure curve, first-order pressure differential curve and second-order pressure differential curve is volt, the unit of pressure is kilopascal, and the unit of capacity is ampere-hour. The pressure change rate threshold in each example is the maximum value of the pressure-capacity first-order differential curve of the battery cell at a rate of 0.1 to 1C in the high SOC range. Example 1 In this example, the layered transition metal oxide NaNi x Fe y Mn 1-x-y O2 (NNFM) is used as the positive electrode, hard carbon (HC) is used as the negative electrode, and polypropylene is used as the separator to assemble a sodium ion soft pack battery. The initial pressure applied to the soft pack battery is 90 kPa, and a conventional carbonate electrolyte is used. In order to avoid the interference of the pressure signal caused by the formation of SEI during the formation process, the formed battery cell was used for testing. Charged to 4V at a rate of 0.2C at 35°C, the pressure signal and capacity signal of the sodium ion battery during the charging process were collected, and the pressure curve, the first-order pressure differential curve and the second-order differential curve were determined according to the pressure signal and the capacity signal. The pressure change rate threshold is the maximum value of the pressure-capacity first-order differential curve of the battery cell at a rate of 1C in the high SOC range. The sodium ion soft pack battery after charging is disassembled to observe the surface morphology of the HC negative electrode after charging at a rate of 0.2C. Example 2 The difference between this embodiment and embodiment 1 is that the charging rate is 1C, and the surface morphology of the HC negative electrode after charging at a rate of 1C is observed, and the other steps are the same as those in embodiment 1. The pressure change rate threshold is the maximum value of the first-order differential curve of the pressure-capacity of the battery cell at a rate of 1C in the high SOC range. Example 3 The difference between this embodiment and embodiment 1 is that the charging rate is 2C, and the surface morphology of the HC negative electrode after charging at a 2C rate is observed, and the other steps are the same as those in embodiment 1. The pressure change rate threshold is the maximum value of the first-order differential curve of the pressure-capacity of the battery cell at a 1C rate in the high SOC range. Effect Example In order to verify the feasibility of using pressure differential curve to detect sodium precipitation in sodium ion soft pack batteries. x Fe y Mn 1-x-y O2 (NNFM) is used as the positive electrode, hard carbon (HC) is used as the negative electrode, and polypropylene is used as a separator to assemble a sodium ion soft pack battery. The initial pressure applied to the soft pack battery is 90 kPa. A conventional carbonate electrolyte is used to charge to 4V at a certain current rate at 35°C. The pressure signal and capacity signal of the sodium ion battery during the charging process are collected, and the charging curve, pressure curve and pressure differential curve are determined according to the pressure signal and capacity signal. Example 1, Example 2 and Example 3 are charged at a rate of 0.5C, 1C and 2C, respectively, and the initial applied pressure is 90 kPa. The sodium ion soft pack battery was disassembled after charging, and the morphology of the HC negative electrode surface was observed using a scanning electron microscope (SEM). The morphology of the HC electrode surface after charging under different conditions, as well as the charging curve, pressure curve, first-order pressure differential curve and second-order pressure differential curve during the charging process are shown in Figure 2. Figure 2-5As shown. It can be seen that when the initial pressure of 90 kPa is applied to the soft pack battery, no sodium precipitation occurs on the HC surface after 0.2C and 1C charging, while sodium precipitation occurs on the HC surface after 2C charging ( Figure 2-4 ). Accordingly, when charging at 0.5C and 1C, the first-order pressure differential curve does not exceed the threshold in the high SOC region, and the second-order pressure differential curve has a point less than 0; when charging at 2C, the first-order pressure differential curve exceeds the threshold in the high SOC region, and the second-order pressure differential curve is always greater than 0 ( Figure 5 ). This shows that this method can quickly and effectively realize real-time monitoring of sodium precipitation at the negative electrode of sodium ion batteries.

Claims

1. A method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery, characterized in that: By monitoring the pressure changes, first-order differential and second-order differential curves of soft-pack sodium-ion batteries during the charge and discharge process, in-situ non-destructive monitoring of sodium precipitation at the negative electrode can be achieved.

2. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 1, characterized in that: The method comprises: using a pressure testing device, comprising an upper clamping plate (1) and a lower clamping plate (2), placing a soft-pack sodium ion battery cell (3) to be tested between the upper clamping plate and the lower clamping plate; installing a pressure sensor (4) and a force-applying rod (5) above the upper clamping plate; the force-applying rod (5) is used to apply pressure to the upper clamping plate so as to clamp the soft-pack sodium ion battery cell (3) to be tested between the upper and lower clamping plates; and the force-applying rod (5) can be locked by a locking nut (6); and the pressure sensor (4) is connected to a pressure online recording system (7).

3. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 2, characterized in that: The following steps are involved: ①Put the soft-pack sodium-ion battery cell to be tested between the upper and lower clamps; ② Rotate the force rod to make the upper and lower clamps clamp the battery cell, and adjust the pressure to the set initial pressure value as needed, and tighten the locking nut; ③ After the pressure value reaches a stable value, the battery cell is charged and discharged using a constant current or constant voltage charge and discharge procedure; ④Online record the pressure value and change law of the sodium ion battery under different charge and discharge conditions; ⑤ Analyze the quantitative relationship between the cell pressure value and the battery charge and discharge capacity, calculate the first-order differential curve and second-order differential curve of pressure changing with charging capacity or voltage, and judge whether sodium precipitation is found in the negative electrode of the sodium-ion battery by whether the first-order differential curve of pressure under high SOC exceeds the predetermined pressure change rate threshold and whether the second-order differential curve is always greater than zero.

4. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 3, characterized in that: The initial pressure value applied by the force-applying rod in ② is 0-500 kPa.

5. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 3, characterized in that: The high SOC mentioned in ⑤ is not less than 50%; the pressure change rate threshold is the maximum value of the first-order differential curve of pressure-capacity of the selected battery cell at a rate of 0.1 to 1C in the high SOC range.

6. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 3, wherein the pressure differential curve is determined according to the pressure signal and the capacity signal, and the steps are as follows: Obtain a curve showing real-time changes in monitoring pressure versus cell capacity; The real-time pressure curve is smoothed and fitted to obtain the pressure-volume function; The first-order differential and the second-order differential of the pressure-volume function with respect to the volume are calculated to obtain the first-order differential curve and the second-order differential curve of pressure.

7. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 3, characterized in that: If the first-order differential curve exceeds the pressure change rate threshold and the second-order differential curve is always greater than 0, it is determined that sodium precipitation has occurred in the sodium ion battery; if the first-order differential curve does not exceed the pressure change rate threshold and the second-order differential curve is less than 0, sodium precipitation has not occurred in the sodium ion battery, and in other cases, no obvious sodium precipitation has occurred.

8. The method for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery according to claim 1, characterized in that: The negative electrode material of the sodium ion battery is a carbon-based material.

9. A device for rapid in-situ monitoring of sodium deposition on the negative electrode side of a soft-pack sodium ion battery, characterized in that: The device comprises an upper clamping plate (1) and a lower clamping plate (2), wherein a soft-pack sodium ion battery to be tested is placed between the upper and lower clamping plates, and a pressure sensor (4) and a force-applying rod (5) are installed above the upper clamping plate. The force-applying rod (5) is used to apply pressure to the upper clamping plate to clamp the soft-pack sodium ion battery cell to be tested (3) between the upper and lower clamping plates, and the force-applying rod (5) can be locked by a locking nut (6). The pressure sensor (4) is connected to a pressure online recording system (7) to record real-time pressure changes, and the soft-pack sodium ion battery to be tested can be charged and discharged simultaneously.

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