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

Abstract

The invention provides a composite additive and a preparation method thereof, sodium ion positive electrode slurry and a high-safety sodium ion soft package battery, the composite additive comprises a phase change heat absorption material and a modified SAPO-LTA molecular sieve, and the mass ratio of the phase change heat absorption material to the modified SAPO-LTA molecular sieve is (0.75-2.25): (1-3); the phase change heat absorption material comprises n-octadecane and sodium nitrate; the modified SAPO-LTA molecular sieve is an SAPO-LTA molecular sieve subjected to cuprous ion replacement and / or lithium ion replacement. According to the invention, the phase change heat absorption material can absorb heat, reduce the temperature rise of the battery cell body and reduce the possibility of chained thermal runaway, and the modified SAPO-LTA molecular sieve has a porous structure, a large specific surface area and a good adsorption effect on gas, can relieve the diffusion of gas in the battery cell, reduce the occurrence of crosstalk reaction and reduce the generation of reaction heat, so that the service life of the battery cell is prolonged, and the service life of the battery cell is prolonged. And the phase change heat absorption material and the modified SAPO-LTA molecular sieve cooperate to reduce the temperature rise of the battery cell, so that the side reaction is reduced, and the needling test passing rate and the safety performance of the sodium ion battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion soft-pack batteries, and particularly relates to a composite additive and a preparation method thereof, a sodium-ion positive electrode paste, and a highly safe sodium-ion soft-pack battery. Background Art

[0002] As a new type of energy storage device, sodium-ion batteries have broad application prospects in fields such as portable electronic devices and electric vehicles due to advantages such as rich raw materials and low cost. However, sodium-ion batteries pose certain challenges in terms of safety. Especially when subjected to external impacts or punctures, the batteries are prone to dangerous situations such as short circuits and thermal runaway.

[0003] Currently, the method generally used to evaluate the safety performance of batteries is the needle-punch test. The purpose of the needle-punch test is to simulate the external mechanical damage (such as impacts, punctures, etc.) that the battery may encounter during actual use, and to evaluate whether the battery will trigger dangerous phenomena such as thermal runaway, fire, and explosion when an internal short circuit occurs. Through the needle-punch test, it can be verified whether the safety design of the battery 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, by adding a protective layer, such as an insulating layer or a lithium iron phosphate layer, on the surface of the electrode material to improve the safety of the battery. However, these measures often increase the processing difficulty and manufacturing cost of the battery cell.

[0005] In addition, current research in the industry on internal heat management and gas diffusion control of batteries is relatively scarce. Especially in the needle-punch test, the high temperature and gas crosstalk reactions generated inside the battery are the key factors leading to thermal runaway. Summary of the Invention

[0006] The purpose of the present invention is to provide a composite additive and a preparation method thereof, a sodium-ion positive electrode paste, and a highly safe sodium-ion soft-pack battery to solve the problems in the above background art.

[0007] The technical solution adopted by the present invention includes: a composite additive, which includes 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 to 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 been replaced with cuprous ions and / or lithium ions.

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

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

[0012] The modified SAPO-LTA molecular sieve and the phase change endothermic material are mixed 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 the reaction is carried out at a constant temperature of 45 to 55° C., for 1.5 to 2.5 hours, and at a stirring speed of 350 to 450 rpm.

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

[0016] The technical solution adopted by the present 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 by the present invention also includes: a highly safe sodium ion soft-pack battery, wherein the positive electrode of the sodium ion soft-pack battery is prepared by a slurry coating method using the sodium ion positive electrode slurry according to claim 8.

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

[0019] The present invention has the following beneficial effects: when a short circuit occurs inside the battery, the composite additive provided by the present invention can absorb heat through the phase-change endothermic material, thereby reducing the temperature rise of the battery cell body and the possibility of chain thermal runaway; the modified SAPO-LTA molecular sieve has a porous structure and a large specific surface area, and has a good adsorption effect on gas, which can alleviate the diffusion of gas 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 body; the phase-change endothermic material and the modified SAPO-LTA molecular sieve synergistically reduce the temperature rise of the battery cell, reduce side reactions, and improve the needle penetration test pass rate and safety performance of the sodium ion battery. Detailed Embodiments

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

[0021] Before elaborating on the specific content of the embodiments of the present invention, we first clarify the possible changes that may occur in a sodium-ion soft-pack battery after being punctured and short-circuited. Puncturing will cause the positive and negative electrodes of the battery to short-circuit, and the short-circuit current will generate Joule heat, resulting in an increase in the internal temperature of the battery; the accumulation of Joule heat will trigger the decomposition of the electrolyte, the decomposition of the SEI film, the decomposition of the positive active material, and side reactions between the positive active material or the negative material and the electrolyte. The above chemical reactions will directly or indirectly generate gases, such as carbon monoxide, carbon dioxide, and hydrogen. Some of these gases will further react with the organic matter in the electrolyte, and these crosstalk reactions release heat, leading to a further increase in the internal temperature of the battery, and even triggering risks such as thermal runaway, fire (combustion of the electrolyte), and explosion.

[0022] The embodiments of the present invention provide a composite additive and its preparation method, as well as a sodium-ion positive electrode slurry and a highly safe sodium-ion soft-pack battery containing this composite additive. When the positive and negative electrodes of the battery are short-circuited, the composite additive absorbs heat and adsorbs gases, reduces the temperature rise of the battery, slows down the crosstalk reaction, and reduces the risks of thermal runaway, fire, and explosion.

[0023] The composite additive includes a phase-change heat-absorbing material and a modified SAPO-LTA molecular sieve with 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 body, and reduce the possibility of chain thermal runaway. The modified SAPO-LTA molecular sieve has a porous structure and a relatively large specific surface area, and has a good adsorption effect on gases, which 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 body; the phase-change heat-absorbing material and the modified SAPO-LTA molecular sieve cooperate to reduce the temperature rise of the battery cell, reduce side reactions, and improve the passing rate of the puncture test and the safety performance of the sodium-ion battery.

[0024] The above-mentioned phase change endothermic material may contain one or more substances. According to the research, exploration and experimental verification of the inventors, the phase change endothermic material preferably contains n-octadecane and sodium nitrate, wherein the phase change temperature of n-octadecane is between 22 and 27°C, and the initial thermal decomposition temperature of the SEI film of the sodium ion battery is 25 to 50°C. When the needle puncture occurs, n-octadecane can absorb the Joule heat generated by the short circuit of the positive and negative electrodes, reduce the temperature rise of the battery cell, inhibit the initial thermal decomposition of the SEI film, slow down its gas production, decomposition and heat release, and directly expose the negative electrode to the electrolyte. The phase change temperature of sodium nitrate is 307 to 308°C, and when the battery cell temperature is 300 to 500°C, it will trigger electrolyte combustion, leading to battery explosion. When crosstalk reaction inevitably occurs in the sodium ion battery, sodium nitrate can absorb the reaction heat, reduce the temperature rise of the battery cell, and avoid electrolyte combustion and battery explosion.

[0025] On the other hand, according to the inventors' research, exploration, and experimental verification, simply using SAPO-LTA molecular sieves to adsorb the gases produced by battery side reactions has a poor effect on improving battery safety. However, modifying the SAPO-LTA molecular sieves with metal cations can adjust the pore size, cell electrostatic field, and other factors, thereby affecting the adsorption performance of the molecular sieve. Therefore, the inventors modified the SAPO-LTA molecular sieves with metal cations to obtain the modified SAPO-LTA molecular sieves described above.

[0026] Among them, in order to increase the adsorption capacity of CO2, 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 interaction forces with gas molecules, and the adsorption capacity of CO2 increases with the decrease of the radius of the alkali metal ion. The radius of the lithium ion is smaller than that of the sodium ion, resulting in more electrostatic surface charge accumulation of the lithium ion than the sodium ion, thereby enabling the lithium ion to produce a stronger electrostatic interaction with molecules having a dipole moment or a quadrupole moment. In addition, the radius of the lithium ion is smaller than that of the sodium ion, and the degree of dispersion of the SAPO-LTA molecular sieve after modification increases, which increases the gaps between the particles, resulting in an increase in the specific surface area and pore volume of the SAPO-LTA molecular sieve after lithium ion replacement modification, and an increase in the adsorption capacity of CO2.

[0027] However, the improvement in the adsorption performance of CO by SAPO-LTA molecular sieve after replacement modification with alkali metal ions or alkaline earth metal ions is not significant. Therefore, the replaced metal cations should also include cuprous ions. The π-complexation between cuprous ions and CO can effectively improve the adsorption performance of CO by SAPO-LTA molecular sieve, and 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 for selective adsorption of CO and increasing the adsorption amount of CO.

[0028] In the exploration of the mutual influence between the temperature rise of the battery cell and the crosstalk reaction, the inventor found that the preferred composition of this composite additive is as follows: 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). Especially when the mass ratio of n-octadecane, sodium nitrate, and modified SAPO-LTA molecular sieve is 1:0.5:2, it can effectively avoid the chain thermal runaway of the battery.

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

[0030] (1) Mix the SAPO-LTA molecular sieve with the modified salt solution, filter, wash, and dry after constant-temperature reaction 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 preferred to perform lithium ion replacement first and then 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 do not have to be limited to the materials provided in this embodiment;

[0032] During the constant-temperature reaction, the temperature is controlled at 45-55°C, preferably 50°C, the time is controlled at 1.5h-2.5h, preferably 2h, and the stirring speed is controlled at 350-450rpm, preferably 400rpm, to ensure the full progress of ion replacement.

[0033] (2) Mix the modified SAPO-LTA molecular sieve with the phase change heat absorption material and dry to obtain the composite additive;

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

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

[0036] According to the research, exploration, and experimental verification of the inventor, the above composite additive accounts for 0.1%-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 20mg / cm 2 ~30mg / cm 2 , and the safety performance of the obtained sodium ion soft-pack battery is better.

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

[0038] Example 1

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

[0040] Mix the SAPO-LTA molecular sieve with a 5 wt% lithium nitrate solution, stir at 400 rpm for 2 h at 50 °C, perform suction filtration and washing, repeat three times, and dry at 90 °C to obtain Li-SAPO-LTA molecular sieve;

[0041] Mix the Li-SAPO-LTA molecular sieve with a 1 wt% cuprous chloride solution, stir at 400 rpm for 2 h at 50 °C, perform suction filtration and washing, and dry at 90 °C to obtain Cu / Li-SAPO-LTA molecular sieve.

[0042] (2) Preparation of composite additive:

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

[0044] Mix the Cu / Li-SAPO-LTA molecular sieve with molten sodium nitrate, stir at 400 rpm for 2 h at 300 °C, and dry at 90 °C;

[0045] Mix the substance obtained in the previous step with n-octadecane, stir at 400 rpm for 2 h at 45 °C, and dry at 35 °C to obtain the composite additive.

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

[0047] Take the positive electrode active material, positive electrode conductive agent, positive electrode binder, and composite additive according to a mass ratio of 95.5%:2.2%:2.2%:0.1%, and homogenize with the positive electrode solvent. Control the solid content of the slurry at 65% to obtain the sodium-ion positive electrode slurry.

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

[0049] (4) Uniformly coat the sodium-ion positive electrode slurry on the aluminum foil, and the coating areal density is 20 mg / cm 2 , to obtain the coated positive electrode sheet;

[0050] Roll the coated positive electrode sheet at a compaction density of 3.1 g / cm 3 to obtain the positive electrode sheet.

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

[0052] Take the negative electrode active material, negative electrode conductive agent, and negative electrode binder in a mass ratio of 95%: 2%: 3%, and use a negative electrode solvent for homogenization. The solid content of the slurry is controlled at 49% to obtain a 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; the negative electrode solvent is water.

[0054] (6) Uniformly coat the negative electrode slurry on the aluminum foil to obtain a coated negative electrode sheet.

[0055] Roll the coated negative electrode sheet at a compaction density of 1.0 g / cm 3 to obtain a negative electrode sheet.

[0056] (7) Cut the negative electrode sheet and the positive electrode sheet into corresponding sizes of sheets, stack them in a Z-shape, and assemble them into a battery stack according to the cycle order of separator - negative electrode - separator - positive electrode.

[0057] (8) Weld the tabs of the assembled battery stack, encapsulate it with an aluminum-plastic film, and perform steps such as baking, liquid injection, formation, and grading to obtain a sodium-ion soft-pack battery.

[0058] Example 2

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

[0060] Example 3

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

[0062] Example 4

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

[0064] Comparative Example 1

[0065] Compared with Example 1, the difference in Comparative Example 1 is only that: in step (3), take the positive electrode active material, positive electrode conductive agent, and positive electrode binder in a mass ratio of 95.6%: 2.2%: 2.2% to prepare the sodium-ion positive electrode slurry, without adding a composite additive.

[0066] Comparative Example 2

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

[0068] Comparative Example 3

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

[0070] Comparative Example 4

[0071] Compared with Example 4, the difference in Comparative Example 4 is only that: in step (2), n-octadecane, sodium nitrate and Cu / Li-SAPO-LTA molecular sieve are taken in 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 complied with GB43854-2024 "Safety Technical Specification 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, the conical angle of the needle tip was 45°) was used to penetrate the geometric center of the battery from the direction perpendicular to the battery plate at a speed of (25±5) mm / s. The steel needle remained in the battery, and it was observed for 1 h.

[0073] The standard charging method of the sodium ion soft-pack battery in this technical solution: before charging, the battery was discharged at a constant current of 0.5C until the discharge cut-off voltage. In a test environment of (23±2)°C, it was charged at 0.2C. When the terminal voltage of the battery reached the charging limit voltage, it was then switched to constant voltage charging until the charging current was less than or equal to 0.02C, and then left standing for 0.5 h.

[0074] The needle penetration test results are shown in the following table:

[0075]

[0076]

[0077] From the needle penetration results of Examples 1 to 4, it can be seen that the sodium ion soft-pack batteries prepared by using the preferred scheme provided by the present invention can all pass the needle penetration test. The battery did not catch fire, explode, or produce a large amount of gas. The temperature rise of the battery core was low, and the risk of chain reaction caused by thermal runaway was significantly reduced; while the needle penetration results of Comparative Examples 1-4 showed that as the coating areal density of the sodium ion positive electrode slurry increased, or the addition amount of the composite additive decreased or the ratio was unbalanced, the needle penetration temperature rise of the battery gradually increased, and accompanied by the appearance of sparks, and the battery case was broken, increasing the possibility of subsequent module thermal runaway.

[0078] It should be understood that the above specific embodiments of the present invention are only for illustrative explanation or interpretation of the principles of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all variations and modifications that fall 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 heat absorption material and a modified SAPO-LTA molecular sieve, and the mass ratio of the two is (0.75 - 2.25):(1 - 3).

2. The composite additive according to claim 1, wherein The phase change heat absorption material includes n-octadecane and sodium nitrate, and the mass ratio of n-octadecane, sodium nitrate to the modified SAPO-LTA molecular sieve is (0.5 - 1.5):(0.25 - 0.75):(1 - 3).

3. The composite additive according to claim 1 or 2, characterized in that, The modified SAPO-LTA molecular sieve is a SAPO-LTA molecular sieve subjected to copper ion replacement and / or lithium ion replacement.

4. A method for preparing the composite additive according to any one of claims 1-3, characterized in that, It includes the steps:[[]]END]] Mix the SAPO-LTA molecular sieve with the modified salt solution, carry out constant temperature reaction, then filter, wash and dry to obtain the modified SAPO-LTA molecular sieve. Mix the modified SAPO-LTA molecular sieve with the phase change heat absorption material and dry to obtain the composite additive.

5. The method for preparing the composite additive according to claim 4, wherein The modified salt solution contains copper ions and / or lithium ions.

6. The method for preparing a composite additive according to claim 4, characterized in that, When mixing the SAPO-LTA molecular sieve with the modified salt solution, during the constant temperature reaction, the temperature condition is 45 - 55 °C, the time is 1.5 h - 2.5 h, and the stirring speed is 350 - 450 rpm.

7. The method for preparing the composite additive according to claim 4, characterized in that, When mixing the modified SAPO-LTA molecular sieve with the phase change heat absorption material, the temperature condition is: greater than or equal to the phase change temperature of the phase change heat absorption material.

8. A sodium ion positive electrode paste, characterized in that, The sodium ion positive electrode slurry contains the composite additive according to any one of claims 1 - 3, and the composite additive accounts for 0.1% - 0.5% of the mass of the sodium ion positive electrode slurry.

9. A highly secure sodium-ion soft-pack battery, characterized in that, The positive electrode of the sodium ion soft-pack battery is prepared by a slurry coating method using the sodium ion positive electrode slurry according to claim 8.

10. The highly secure sodium-ion soft-pack battery according to claim 9, wherein, The coating areal density of the sodium ion positive electrode paste is 20 mg / cm 2 ~30 mg / cm 2 .

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