Composite additive, preparation method thereof, sodium ion positive electrode slurry and high-safety sodium ion soft package battery

Abstract

The application provides a composite additive and a preparation method, a sodium ion positive electrode slurry and a high-safety sodium ion soft package battery. The composite additive comprises a phase change endothermic material and modified SAPO-LTA molecular sieve, and the mass ratio of the two is (0.75-2.25):(1-3). The phase change endothermic material comprises n-octadecane and sodium nitrate. The modified SAPO-LTA molecular sieve is SAPO-LTA molecular sieve subjected to cuprous ion substitution and / or lithium ion substitution. In the application: the phase change endothermic material can absorb heat, reduce the temperature rise of the battery body, reduce the possibility of chain thermal runaway, the modified SAPO-LTA molecular sieve has a porous structure, a relatively large specific surface area and a good adsorption effect on gas, can relieve the diffusion of gas in the battery body, reduce the occurrence of crosstalk reaction, reduce the generation of reaction heat, reduce the temperature rise of the battery body, the phase change endothermic material and the modified SAPO-LTA molecular sieve cooperatively reduce the temperature rise of the battery, reduce side reactions, and improve the needle test passing rate and safety performance of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion pouch battery technology, and in particular to a composite additive and its preparation method, a sodium-ion positive electrode slurry, and a high-safety sodium-ion pouch battery. Background Technology

[0002] Sodium-ion batteries, as a novel energy storage device, have broad application prospects in portable electronic devices, electric vehicles, and other fields due to their advantages such as abundant raw materials and low cost. However, sodium-ion batteries face certain safety challenges, especially when subjected to external impacts or punctures, as they are prone to dangerous situations such as short circuits and thermal runaway.

[0003] Currently, the common method used to assess battery safety performance is the nail penetration test. The purpose of the nail penetration test is to simulate external mechanical damage (such as impact, puncture, etc.) that a battery may encounter during actual use, and to assess whether the battery will cause dangerous phenomena such as thermal runaway, fire, or explosion when an internal short circuit occurs. Through the nail penetration test, it can be verified whether the battery's safety design can effectively prevent or mitigate these potential safety risks.

[0004] On the other hand, current research on the safety of sodium-ion batteries mainly focuses on material modification and structural design. For example, adding protective layers, such as insulating layers or lithium iron phosphate layers, to the surface of electrode materials can improve battery safety. However, these measures often increase the processing difficulty and manufacturing cost of the battery cells.

[0005] Furthermore, there is relatively little research in the industry on internal thermal management and gas diffusion control of batteries, especially in nail penetration tests, where the high temperature and gas crosstalk reactions generated inside the battery are key factors leading to thermal runaway. Summary of the Invention

[0006] The purpose of this invention is to provide a composite additive and its preparation method, a sodium-ion positive electrode slurry, and a high-safety sodium-ion soft-pack battery to solve the problems mentioned in the background art.

[0007] The technical solution adopted in this invention includes: a composite additive, wherein the composite additive comprises a phase change endothermic material and a modified SAPO-LTA molecular sieve, and the mass ratio of the two is (0.75~2.25):(1~3).

[0008] Preferably, the phase change endothermic material includes n-octadecane and sodium nitrate, and the mass ratio of n-octadecane, sodium nitrate and the modified SAPO-LTA molecular sieve is (0.5-1.5):(0.25-0.75):(1-3).

[0009] Preferably, the modified SAPO-LTA molecular sieve is a SAPO-LTA molecular sieve that has undergone cuprous ion replacement and / or lithium ion replacement.

[0010] The technical solution adopted in this invention also includes: a method for preparing the above-mentioned composite additive, which includes the following steps:

[0011] SAPO-LTA molecular sieve was mixed with modified salt solution, reacted at a constant temperature, filtered, washed and dried to obtain modified SAPO-LTA molecular sieve.

[0012] The modified SAPO-LTA molecular sieve was mixed with a phase change endothermic material and dried to obtain a composite additive.

[0013] Preferably, the modified salt solution contains cuprous ions and / or lithium ions.

[0014] Preferably, the SAPO-LTA molecular sieve is mixed with the modified salt solution and reacted at a constant temperature of 45-55°C for 1.5-2.5 hours and a stirring speed of 350-450 rpm.

[0015] Preferably, when the modified SAPO-LTA molecular sieve is mixed with the phase change heat-absorbing material, the temperature condition is: greater than or equal to the phase change temperature of the phase change heat-absorbing material.

[0016] The technical solution adopted in this invention also includes: a sodium ion positive electrode slurry, wherein the sodium ion positive electrode slurry contains the above-mentioned composite additive, and the composite additive accounts for 0.1% to 0.5% of the mass of the sodium ion positive electrode slurry.

[0017] The technical solution adopted in this invention also includes: a high-safety sodium-ion soft-pack battery, wherein the positive electrode of the sodium-ion soft-pack battery is prepared by the above-mentioned sodium-ion positive electrode slurry through a slurry coating method.

[0018] Preferably, the coating surface density of the sodium ion positive electrode slurry is 20 mg / cm³. 2 ~30mg / cm 2 .

[0019] The beneficial effects of this invention are as follows: When a short circuit occurs inside the battery, the phase change heat-absorbing material provided by this invention can absorb heat, reduce the temperature rise of the battery cell, and reduce the possibility of chain thermal runaway. The modified SAPO-LTA molecular sieve has a porous structure and a large specific surface area, which has a good adsorption effect on gases, can alleviate the diffusion of gases inside the battery cell, reduce the occurrence of crosstalk reactions, reduce the generation of reaction heat, and reduce the temperature rise of the battery cell. The phase change heat-absorbing material and the modified SAPO-LTA molecular sieve work together to reduce the temperature rise of the battery cell, reduce side reactions, and improve the nail penetration test pass rate and safety performance of sodium-ion batteries. Detailed Implementation

[0020] The embodiments of the present invention are described in detail below.

[0021] Before describing the specific details of the embodiments of the present invention, we first clarify the possible changes that may occur in a sodium-ion pouch battery after a needle puncture short circuit. A needle puncture causes a short circuit between the positive and negative electrodes of the battery. The short-circuit current induces Joule heating, leading to an increase in the internal temperature of the battery. The accumulation of Joule heating can trigger electrolyte decomposition, SEI film decomposition, positive electrode active material decomposition, and side reactions between the positive or negative electrode materials and the electrolyte. These chemical reactions can directly or indirectly produce gases, such as carbon monoxide, carbon dioxide, and hydrogen. Some of these gases can then react with organic matter in the electrolyte in a series of side reactions. These crosstalk reactions release heat, causing the internal temperature of the battery to rise further, and even leading to risks such as thermal runaway, fire (electrolyte combustion), and explosion.

[0022] This invention provides a composite additive and its preparation method, as well as a sodium-ion positive electrode slurry containing this composite additive and a high-safety sodium-ion soft-pack battery. The composite additive absorbs heat and adsorbs gas when a short circuit occurs at the positive and negative electrodes of the battery, thereby reducing the battery temperature rise, mitigating crosstalk reactions, and reducing the risk of thermal runaway, fire, and explosion.

[0023] This composite additive comprises a phase change heat-absorbing material and a modified SAPO-LTA molecular sieve in a mass ratio of (0.75–2.25):(1–3). When a short circuit occurs inside the battery, the phase change heat-absorbing material can absorb heat, reduce the temperature rise of the battery cell, and reduce the possibility of chain thermal runaway. The modified SAPO-LTA molecular sieve has a porous structure and a large specific surface area, which has a good adsorption effect on gases, can alleviate the diffusion of gases inside the battery cell, reduce the occurrence of crosstalk reactions, reduce the generation of reaction heat, and reduce the temperature rise of the battery cell. The phase change heat-absorbing material and the modified SAPO-LTA molecular sieve work together to reduce the temperature rise of the battery cell, reduce side reactions, and improve the nail penetration test pass rate and safety performance of sodium-ion batteries.

[0024] The aforementioned phase change heat-absorbing material may contain one or more substances. According to the inventor's research, exploration, and experimental verification, the preferred phase change heat-absorbing material contains n-octadecane and sodium nitrate. The phase change temperature of n-octadecane is between 22 and 27°C, while the initial thermal decomposition temperature of the SEI film in a sodium-ion battery is between 25 and 50°C. When needle puncture occurs, n-octadecane can absorb the Joule heat generated by the short circuit between the positive and negative electrodes, reduce the cell temperature rise, inhibit the initial thermal decomposition of the SEI film, and slow down the rate of gas production, decomposition heat release, and direct exposure of the negative electrode to the electrolyte. The phase change temperature of sodium nitrate is 307 to 308°C, while the electrolyte combustion will occur when the cell temperature is between 300 and 500°C, leading to battery explosion. When crosstalk reaction inevitably occurs in a sodium-ion battery, sodium nitrate can absorb the heat of reaction, reduce the cell temperature rise, and prevent electrolyte combustion and battery explosion.

[0025] On the other hand, according to the inventors' research, exploration, and experimental verification, simply adsorbing the aforementioned gases generated by battery side reactions using SAPO-LTA molecular sieves has a poor effect on improving battery safety. However, modifying SAPO-LTA molecular sieves with metal cation replacement can modulate the pore size and electrostatic field of the crystal cavities, thereby affecting the adsorption performance of the molecular sieve. Therefore, the inventors modified SAPO-LTA molecular sieves with metal cation replacement to obtain the aforementioned modified SAPO-LTA molecular sieve.

[0026] To improve CO2 adsorption capacity, the replaced metal cations should include alkali metal ions or alkaline earth metal ions, preferably lithium ions. Alkali metal ions and alkaline earth metal ions have strong interactions with gas molecules, and the CO2 adsorption capacity increases with decreasing alkali metal ion radius. Lithium ions have a smaller radius than sodium ions, resulting in more electrostatic surface charge accumulation. This allows lithium ions to generate stronger electrostatic interactions with molecules possessing dipole or quadrupole moments. Furthermore, the smaller radius of lithium ions compared to sodium ions, coupled with the increased dispersion of the modified SAPO-LTA molecular sieve, leads to more interparticle gaps, resulting in increased specific surface area and pore volume of the lithium-ion-modified SAPO-LTA molecular sieve, thus increasing CO2 adsorption capacity.

[0027] However, the improvement in CO adsorption performance of SAPO-LTA molecular sieve after replacement with alkali metal ions or alkaline earth metal ions is not significant. Therefore, the replacement metal cations should also include cuprous ions. The π-complexation of cuprous ions with CO can effectively improve the CO adsorption performance of SAPO-LTA molecular sieve. Furthermore, cuprous ions can be dispersed in a monolayer on the surface of the molecular sieve, thereby providing a large number of cuprous ion adsorption sites, selectively adsorbing CO, and increasing the amount of CO adsorbed.

[0028] In their investigation into the interaction between cell temperature rise and crosstalk reaction, the inventors discovered that the preferred composition of this composite additive is: the mass ratio of n-octadecane, sodium nitrate, and modified SAPO-LTA molecular sieve is (0.5-1.5):(0.25-0.75):(1-3). In particular, when the mass ratio of n-octadecane, sodium nitrate, and modified SAPO-LTA molecular sieve is 1:0.5:2, it can effectively prevent the battery from experiencing chain thermal runaway.

[0029] The method for preparing the above-mentioned composite additive includes the following steps:

[0030] (1) The SAPO-LTA molecular sieve was mixed with the modified salt solution, reacted at a constant temperature, filtered, washed and dried to obtain the modified SAPO-LTA molecular sieve.

[0031] In this step, the modified salt solution contains cuprous ions and / or lithium ions. To avoid crosstalk during the replacement process, it is preferable to perform lithium ion replacement first, followed by cuprous ion replacement. In this embodiment, lithium nitrate solution is used for lithium ion replacement, and cuprous chloride solution is used for cuprous ion replacement. Those skilled in the art can select materials according to actual needs and are not limited to the materials provided in this embodiment.

[0032] During the isothermal reaction, the temperature is controlled at 45-55℃, preferably 50℃, the time is controlled at 1.5h-2.5h, preferably 2h, and the stirring speed is controlled at 350-450rpm, preferably 400rpm, to ensure that the ion exchange is fully carried out.

[0033] (2) The modified SAPO-LTA molecular sieve was mixed with the phase change heat-absorbing material and dried to obtain a composite additive;

[0034] In this step, the temperature conditions should be controlled to be greater than or equal to the phase change temperature of the phase change endothermic material. To avoid crosstalk, it is preferable to first mix sodium nitrate and modified SAPO-LTA molecular sieve, and then mix n-octadecane.

[0035] After the composite additive is prepared, it can be added to the sodium-ion positive electrode slurry and homogenized together. The positive electrode of the sodium-ion soft-pack battery can be prepared by the slurry coating method. Then, it can be assembled with the negative electrode, electrolyte and other functional components to obtain a highly safe sodium-ion soft-pack battery.

[0036] Based on the inventor's research, exploration, and experimental verification, the aforementioned composite additive accounts for 0.1% to 0.5% of the mass of the sodium ion positive electrode slurry, and the coating surface density of the sodium ion positive electrode slurry is 20 mg / cm³. 2 ~30mg / cm 2 The resulting sodium-ion pouch battery has superior safety performance.

[0037] The following are specific embodiments and comparative examples of the present invention.

[0038] Example 1

[0039] (1) Preparation of modified SAPO-LTA molecular sieves:

[0040] SAPO-LTA molecular sieve was mixed with 5wt% lithium nitrate solution, stirred at 400rpm for 2h at 50℃, filtered and washed, repeated three times, and dried at 90℃ to obtain Li-SAPO-LTA molecular sieve.

[0041] The Li-SAPO-LTA molecular sieve was mixed with a 1 wt% cuprous chloride solution, stirred at 400 rpm for 2 h at 50 °C, filtered and washed, and dried at 90 °C to obtain Cu / Li-SAPO-LTA molecular sieve.

[0042] (2) Preparation of composite additives:

[0043] Use n-octadecane, sodium nitrate, and Cu / Li-SAPO-LTA molecular sieve in a mass ratio of 1:0.5:2;

[0044] The Cu / Li-SAPO-LTA molecular sieve was mixed with molten sodium nitrate, stirred at 300℃ and 400rpm for 2h, and then dried at 90℃.

[0045] The substance obtained in the previous step was mixed with n-octadecane, stirred at 400 rpm for 2 hours at 45°C, and dried at 35°C to obtain the composite additive.

[0046] (3) Preparation of sodium ion positive electrode slurry:

[0047] The positive electrode active material, positive electrode conductive agent, positive electrode binder and composite additive are taken in a mass ratio of 95.5%:2.2%:2.2%:0.1%, and homogenized with positive electrode solvent. The solid content of the slurry is controlled at 65% to obtain sodium ion positive electrode slurry.

[0048] The positive electrode active material is sodium-ion oxide; the positive electrode conductive agent includes conductive carbon black and carbon nanotubes; the positive electrode binder includes polyvinylidene fluoride; and the positive electrode solvent is N-methylpyrrolidone.

[0049] (4) The sodium ion positive electrode slurry is uniformly coated onto the aluminum foil, with a coating density of 20 mg / cm³. 2 The coated positive electrode sheet is obtained;

[0050] The coated positive electrode sheet was prepared at a ratio of 3.1 g / cm³. 3 The compaction density is rolled to obtain the positive electrode sheet.

[0051] (5) Preparation of negative electrode slurry:

[0052] The negative electrode active material, negative electrode conductive agent and negative electrode binder are taken in a mass ratio of 95%:2%:3%, and homogenized using negative electrode solvent. The solid content of the slurry is controlled at 49% to obtain the negative electrode slurry.

[0053] The negative electrode active material is hard carbon; the negative electrode conductive agent includes conductive carbon black and carbon nanotubes; the negative electrode binder includes sodium carboxymethyl cellulose and styrene-butadiene rubber; and the negative electrode solvent is water.

[0054] (6) The negative electrode slurry is uniformly coated onto the aluminum foil to obtain the coated negative electrode sheet;

[0055] The coated negative electrode sheet was prepared at a ratio of 1.0 g / cm². 3 The compaction density is rolled to obtain the negative electrode sheet.

[0056] (7) Cut the negative electrode and positive electrode into corresponding sizes, stack them in a Z-shape, and assemble them into a battery electrode assembly in the cyclic sequence of separator-negative electrode-separator-positive electrode.

[0057] (8) Weld the assembled battery electrode group to the tabs, encapsulate it with aluminum-plastic film, and perform baking, liquid injection, formation and capacity testing to obtain sodium-ion soft pack battery.

[0058] Example 2

[0059] Compared with Example 1, the only difference in Example 2 is that n-octadecane, sodium nitrate and Cu / Li-SAPO-LTA molecular sieve are used in step (2) in a mass ratio of 1.5:0.5:2.

[0060] Example 3

[0061] Compared with Example 1, the only difference in Example 3 is that in step (3), the positive electrode active material, positive electrode conductive agent, positive electrode binder and composite additive are taken in a mass ratio of 95.1%:2.2%:2.2%:0.5%.

[0062] Example 4

[0063] Compared with Example 1, the only difference in Example 4 is that the coating surface density of the sodium ion positive electrode slurry in step (4) is 30 mg / cm³. 2 .

[0064] Comparative Example 1

[0065] Compared with Example 1, the only difference in Comparative Example 1 is that in step (3), the positive electrode active material, positive electrode conductive agent and positive electrode binder are used in a mass ratio of 95.6%:2.2%:2.2% to prepare sodium ion positive electrode slurry, and no composite additives are added.

[0066] Comparative Example 2

[0067] Compared with Example 1, the only difference in Comparative Example 2 is that the coating surface density of the sodium ion positive electrode slurry in step (4) is 40 mg / cm³. 2 .

[0068] Comparative Example 3

[0069] Compared with Example 4, the only difference in Comparative Example 3 is that n-octadecane, sodium nitrate and Cu / Li-SAPO-LTA molecular sieve were used in step (2) at a mass ratio of 0:0:2.

[0070] Comparative Example 4

[0071] Compared with Example 4, the only difference in Comparative Example 4 is that n-octadecane, sodium nitrate and Cu / Li-SAPO-LTA molecular sieve were used in step (2) at a mass ratio of 1:0.5:0.5.

[0072] The sodium-ion soft-pack batteries prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to a needle penetration test. The test conditions followed GB43854-2024 "Safety Technical Specifications for Lithium-ion Batteries for Electric Bicycles". Specifically, after the battery was fully charged according to the standard charging test method, a high-temperature resistant steel needle with a diameter of 5 mm (such as tungsten steel, with a cone angle of 45° at the needle tip) was used to penetrate the geometric center of the battery from a direction perpendicular to the battery plates at a speed of (25±5) mm / s. The steel needle remained in the battery and was observed for 1 hour.

[0073] The standard charging method for sodium-ion pouch batteries in this technical solution is as follows: Before charging, the battery is discharged at a constant current of 0.5C until the discharge termination voltage. Under a test environment of (23±2)℃, it is charged at 0.2C. When the battery terminal voltage reaches the charging limit voltage, it is then charged at a constant voltage until the charging current is less than or equal to 0.02C, and then left to stand for 0.5 hours.

[0074] The results of the acupuncture test are shown in the table below:

[0075]

[0076] As can be seen from the needle penetration results of Examples 1-4, the sodium-ion soft-pack batteries prepared using the preferred scheme provided by the present invention can all pass the needle penetration test. The batteries did not catch fire, explode, or generate gas significantly. The cell temperature rise was low, and the risk of thermal runaway leading to a chain reaction was significantly reduced. However, the needle penetration results of Comparative Examples 1-4 show that as the coating density of the sodium-ion positive electrode slurry increases, or the amount of composite additives decreases or the ratio becomes unbalanced, the needle penetration temperature rise of the battery gradually increases, accompanied by the appearance of sparks. The battery casing is broken, increasing the possibility of thermal runaway in the subsequent module.

[0077] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the claims, or equivalent forms of such scope and boundaries.

Claims

1. A composite additive, characterized in that, The composite additive includes a phase change endothermic material and a modified SAPO-LTA molecular sieve, with a mass ratio of (0.75–2.25):(1–3); the phase change endothermic material includes n-octadecane and sodium nitrate, with a mass ratio of n-octadecane, sodium nitrate, and the modified SAPO-LTA molecular sieve of (0.5–1.5):(0.25–0.75):(1–3); the modified SAPO-LTA molecular sieve is a SAPO-LTA molecular sieve that has undergone cuprous ion replacement and lithium ion replacement.

2. The method for preparing the composite additive according to claim 1, characterized in that, Including the following steps: SAPO-LTA molecular sieve was mixed with modified salt solution, reacted at a constant temperature, filtered, washed and dried to obtain modified SAPO-LTA molecular sieve. The modified SAPO-LTA molecular sieve was mixed with a phase change endothermic material and dried to obtain a composite additive.

3. The method for preparing composite additives according to claim 2, characterized in that, The modified salt solution contains cuprous ions and lithium ions.

4. The method for preparing composite additives according to claim 2, characterized in that, The SAPO-LTA molecular sieve was mixed with the modified salt solution and reacted at a constant temperature of 45-55℃ for 1.5-2.5 hours and a stirring speed of 350-450 rpm.

5. The method for preparing composite additives according to claim 2, characterized in that, When the modified SAPO-LTA molecular sieve is mixed with the phase change heat-absorbing material, the temperature condition is: greater than or equal to the phase change temperature of the phase change heat-absorbing material.

6. A sodium ion positive electrode slurry, characterized in that, The sodium ion cathode slurry contains the composite additive as described in claim 1, wherein the composite additive accounts for 0.1% to 0.5% of the mass of the sodium ion cathode slurry.

7. A highly safe sodium-ion soft-pack battery, characterized in that, The positive electrode of the sodium-ion pouch battery is prepared by means of the sodium-ion positive electrode slurry described in claim 6 through a slurry coating method.

8. The high-safety sodium-ion soft-pack battery according to claim 7, characterized in that, The coating surface density of the sodium ion positive electrode slurry is 20 mg / cm³. 2 ~30mg / cm 2 .

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