Controllable rupture type alkaline electrolyte microcapsule and preparation method thereof

Abstract

The preparation method comprises the following steps: preparing a sodium alginate SA solution and a chitosan CS solution, and carrying out modification treatment on polylactic acid PLA; preparing a mixed solution of SA, CS and PLA, and synchronously injecting electrolyte and a wall material into the mixed solution by using a high-pressure microcapsule embedding machine; dropping the liquid drops into curing liquid containing 2% of CaCl2, and curing for 30 minutes; and after filtering, transferring the capsule to a vacuum drying oven for 2 hours. The controllable rupture type alkaline electrolyte microcapsule is added into the battery, and can rupture and release the electrolyte as required in the middle period of the service life of the battery, so that the consumed electrolyte is supplemented in real time, and the cycle life of the battery is remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a controllable rupture type alkaline electrolyte microcapsule and a preparation method thereof. BACKGROUND

[0002] With the rapid growth of the world population and the rapid development of the global economy, the overuse of fossil energy has led to corresponding environmental problems. In order to cope with this challenge, humans have begun to explore the application of clean energy such as hydroelectric power, solar energy, wind energy, and geothermal energy. However, such energy sources have intermittency, volatility, and uncontrollability, and direct integration into the power grid will cause an impact on the power grid. Therefore, efficient energy storage and conversion devices are needed to ensure the effective integration and utilization of clean energy.

[0003] Among the various types of electrochemical energy storage devices, lithium-ion batteries with high energy density and long cycle life have dominated the energy storage market and are widely used in electronic devices, electric or hybrid vehicles, and other fields. However, the further development of lithium-ion batteries still faces some difficult problems, such as the high activity of electrode materials, the safety problems of flammable and volatile organic electrolytes, and the limited nature of lithium resources.

[0004] In recent years, aqueous electrochemical energy storage systems have received widespread attention due to their inherent safety, low cost, non-toxicity, high ionic conductivity, and fast charge transport, which are conducive to the development of large-scale energy storage systems and are also suitable for use as power batteries. Alkaline aqueous batteries have inherent high safety and high voltage potential, and have always been a popular research topic. In the development process of rechargeable alkaline batteries for more than 100 years, the positive electrode material has always been high-performance nickel hydroxide, while the negative electrode material has undergone several generations of evolution, including iron, cadmium, metal hydride, and zinc.

[0005] Rechargeable alkaline batteries are mainly designed in a liquid-lean manner, which has good safety, excellent leak-proof performance, high temperature resistance, and strong high-rate discharge performance, while eliminating the need for liquid electrolyte storage space in traditional batteries, making the battery smaller and lighter in weight, and widely used in consumer electronics. However, due to the small amount of electrolyte and the easy decomposition and consumption of water-soluble solvents (such as nickel-zinc batteries and some nickel-hydrogen batteries), the cycle life of the battery is relatively short. The current method of extending the life of lead-acid batteries by supplementing electrolyte is relatively mature, and the method of extending the life of lithium batteries by supplementing lithium is also widely studied, but there is no method to extend the life of liquid-lean alkaline batteries by supplementing electrolyte. SUMMARY

[0006] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a controllable rupture type alkaline electrolyte microcapsule and a preparation method thereof.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a controllable rupture type alkaline electrolyte microcapsule, the controllable rupture type alkaline electrolyte microcapsule comprising:

[0008] Capsule core: the content is alkaline electrolyte;

[0009] Capsule wall: composed of sodium alginate, chitosan and polylactic acid, with the mass fraction of sodium alginate being 30-70wt%, chitosan being 10-30wt%, and polylactic acid being 20-50wt%. The capsule wall thickness is 15-25μm, and the microcapsule diameter is 400-600μm.

[0010] As a further improvement of the present invention: the composite ratio of sodium alginate, chitosan and polylactic acid is 8:2:2 to 3:2:7.

[0011] As a further improvement of the present invention: the composite ratio of sodium alginate, chitosan and polylactic acid is 5:2:3.

[0012] The present invention also includes a method for preparing controllable rupture alkaline electrolyte microcapsules, comprising the following steps:

[0013] S1: Prepare sodium alginate SA solution and chitosan CS solution to modify polylactic acid PLA;

[0014] S2: Prepare a mixed solution of SA, CS, and PLA, and inject the electrolyte and wall material into the mixed solution simultaneously using a high-pressure microencapsulation machine;

[0015] S3: drop the liquid into a 2% CaCl2 solidification solution and solidify for 30 minutes;

[0016] S4: After filtration, the capsules were transferred to a vacuum drying oven for 2 hours.

[0017] As a further improvement of the present invention: the preparation of the SA solution comprises the following steps:

[0018] Sodium alginate was dissolved in deionized water at a concentration of 2-5% w / v and stirred magnetically until completely dissolved; 0.5-1% sodium citrate was added.

[0019] As a further improvement of the present invention: the preparation of the CS solution comprises the following steps:

[0020] CS was dissolved in 1% acetic acid solution to a concentration of 2-4% w / v, and 0.1% polysorbate 80 was added.

[0021] As a further improvement of the present invention: the polylactic acid PLA modification process comprises the following steps:

[0022] The low molecular weight PLA is dissolved in dichloromethane, the concentration of dichloromethane is 5-8% w / v, and 10% polyethylene glycol is added.

[0023] As a further improvement of the present application: the solidification liquid of CaCl2 in step S4 contains 0.1M NaCl, 0.1% chitosan and pH=5.

[0024] As a further improvement of the present application: in step S2, the inner needle of the high-pressure microcapsule embedding machine is 0.5-0.8mm, the outer needle is 1.0-1.5mm, the control electrolyte flow rate is 10-15μL / min, the control wall material solution flow rate is 20-30μL / min, the voltage is 20-25kV, the electrode plate spacing is 10-15cm, and the droplet forming frequency is 50-100Hz.

[0025] As a further improvement of the present application: in step S2, the inner needle of the high-pressure microcapsule embedding machine is 0.5mm for electrolyte, the outer needle is 1.2mm for wall material, the electrolyte flow rate is 14μL / min, the wall material solution flow rate is 26μL / min, the voltage is 23kV, the electrode plate spacing is 14cm, and the droplet forming frequency is 70Hz.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] For poor liquid alkaline batteries, especially secondary batteries, after multiple charge and discharge cycles, the electrolyte is consumed, the internal resistance of the battery increases, and the capacity decreases. By adding the controllable broken alkaline electrolyte microcapsule of the present application to the alkaline battery, the electrolyte can be supplemented in the middle life of the alkaline battery, thereby prolonging the service life of the battery. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] It has to be noted that, as used herein, the terms "comprising", "including", "containing", "characterized by", "comprised of", and grammatical equivalents thereof are used herein to mean one or more steps do not inherently require other steps, elements or ingredients which are set forth. In some embodiments, process, method, article or apparatus includes, but is not limited to, a corresponding process, method, article, or apparatus that comprises, consists of, consists essentially of, or consists of the steps or elements only. It should also be understood that the order of steps or order for accessing or manipulating the various steps can be changed or interchanged without departing from the scope of the application, except where characteristically described by order dependency. Accordingly, where a process, method, article, or apparatus does not include an explicitly recited step, it is to be assumed that that step is optional and does not necessarily have to be included. Additionally, other steps or elements not specifically recited can be added or removed depending on the application or process. Other steps or elements can also be added or removed from these processes.

[0030] With the large-scale access of clean energy (such as hydropower, solar energy, wind energy, geothermal energy) to the power grid, the demand for efficient and safe electrochemical energy storage devices is increasingly prominent. Among the many energy storage options, lithium-ion batteries dominate due to their high energy density and long cycle life, but still face problems such as flammable, organic electrolyte volatile leakage may cause fire, high-purity lithium resources are scarce and the cost continues to rise. In contrast, aqueous electrochemical energy storage systems are becoming a strong competitor for large-scale energy storage and power batteries due to their non-toxic, safe, low-cost, high ionic conductivity, and other advantages. Among them, rechargeable alkaline batteries (mainly using nickel hydroxide positive electrode, multiple negative electrode materials evolve to nickel-hydrogen, zinc, etc.) have a hundred-year development history, and with the "poor liquid type" design - that is, most of the electrolyte is solidified or a small amount of prepositioning - it achieves excellent high-temperature resistance, leakage prevention performance; high-rate discharge capability; smaller and lighter battery volume structure; wide range of consumer electronics applications. Existing such as CN201710467763.0 A kind of lithium battery electrolyte microcapsule control acid additive and preparation method in which acid or basic small molecule is coated with high-temperature resistant resin to achieve absorption and delayed release of corrosive gases (such as HF); the high-temperature resin material used has insufficient chemical stability in a strong alkaline aqueous environment, is prone to swelling or cracking, and cannot guarantee long-term, controlled release of alkaline electrolyte; at the same time, its design focuses on gas absorption and is not suitable for liquid "liquid supplementing" requirements. Another temperature-triggered breakage microcapsule uses a polystyrene / polyethylene double-layer capsule wall to coat a silicone resin capsule core, and releases a fire retardant by triggering breakage at an external high temperature; however, the poor liquid alkaline battery has a limited temperature range (-20 to +60°C) during normal operation, making it difficult to trigger accurately; polystyrene and polyethylene are easily eroded or physically expanded in strong alkali (KOH), making it difficult to maintain the stability and mechanical strength of the capsule wall for several months to several years; the preparation process is relatively complex, and the capsule core is mainly silicone resin, which cannot support high-concentration aqueous electrolyte. The existing microcapsule needs to be chemically and mechanically stable in a high-concentration alkaline environment; at the same time, it needs to efficiently store aqueous electrolyte without adverse reactions with the wall material. It should be matched with the battery operating state, neither too early release nor delayed to damage the battery. The cycle needs to cover the entire service life of the battery, and the release amount and rate need to be highly matched with the electrolyte consumption rate. Particle size uniformity, wall thickness controllability, and production scalability should be considered; after release, the electrolyte needs to be quickly replenished to conduct ions and not introduce impurities, minimizing the negative impact on the electrode interface and the separator.

[0031] To solve the above problems, the application provides a controllable breakage type alkaline electrolyte microcapsule and a preparation method thereof. During the middle period of battery use, the microcapsule spontaneously breaks down at a predetermined time, releasing alkaline electrolyte quantitatively without the need for external maintenance or manual liquid addition; significantly improving voltage drop and energy loss during high-rate discharge.

[0032] A controllable rupture type alkaline electrolyte microcapsule, the controllable rupture type alkaline electrolyte microcapsule comprising: a capsule core: the content is an alkaline electrolyte; a capsule wall: compounded by sodium alginate, chitosan and polylactic acid, and the mass fraction of sodium alginate is 30-70wt%, the chitosan is 10-30wt%, and the polylactic acid is 20-50wt%, the capsule wall thickness is 15-25μm, and the microcapsule diameter is 400-600μm.

[0033] A preparation method of a controllable rupture type alkaline electrolyte microcapsule, comprising the following steps:

[0034] S1: preparing a sodium alginate SA solution, a chitosan CS solution, and modifying and treating polylactic acid PLA;

[0035] S2: preparing a mixed solution of SA, CS and PLA, and synchronously injecting the electrolyte and the wall material by using a high-pressure microcapsule embedding machine;

[0036] S3: dropping the liquid drops into a solidification liquid of 2% CaCl2 and solidifying for 30 minutes;

[0037] S4: after filtration, transferring the capsules to a vacuum drying box for 2 hours.

[0038] By using the ternary compound capsule wall of sodium alginate (SA), chitosan (CS) and polylactic acid (PLA), the wall thickness of 15-25μm and the particle size of 400-600μm, the mechanical strength and the degradation rate of the capsule wall can be accurately controlled, the alkaline electrolyte can be released quantitatively in a predetermined period (for example, 3-12 months), and the function of "internal liquid supplementing" can be realized. The PLA provides a good alkali-resistant skeleton for the capsule wall, the SA / CS compound network is not easy to swell, crack or react with the electrolyte in a strong alkali (KOH) environment, and the long-term storage stability and service life of the microcapsule are greatly improved. By using the high-pressure microcapsule embedding machine to synchronously inject the capsule core electrolyte and the wall material mixed solution, the CS plays a cross-linking and reinforcing role in the capsule wall, so that the microcapsule is not easy to be damaged during transportation, assembly and battery loading, and the leakage of the capsule core electrolyte in the release period is avoided. The whole water system preparation process has little inorganic solvent residue; the release trigger only depends on the degradation of the capsule wall or the external weak pH / humidity change, and does not need high temperature or chemical additives, thereby avoiding the leakage and thermal runaway risk of traditional organic electrolyte.

[0039] As an embodiment of the present application, by adjusting the proportions of sodium alginate (SA), chitosan (CS) and polylactic acid (PLA), microcapsules with different rupture times can be obtained. The diameter of the microcapsules prepared by the present application is about 500μm, and by using the mixed solution of SA, CS and PLA in proportions from 8:2:2 to 3:2:7, microcapsules with rupture times from 1 month to 1 year can be designed.

[0040] In the embodiment, the rupture time is set to 3 to 6 months.

[0041] As an embodiment of the present application, the SA solution preparation comprises the following steps:

[0042] Dissolve SA in deionized water at a concentration of 2-5% (w / v) and stir by magnetic stirring (50°C, 500 rpm) until completely dissolved to avoid clumping. Add 0.5-1% sodium citrate as a chelating agent to prevent Ca 2+ Premature cross-linking causes the solution to gel, while improving the alkali resistance of the wall material.

[0043] As an embodiment of the present application, the CS solution preparation comprises the following steps:

[0044] Dissolve CS in 1% acetic acid solution at a concentration of 2-4% (w / v) and pH≈4.0. After stirring, let stand to degas. Add 0.1% Tween 80 (Polysorbate-80) to reduce surface tension and enhance polyelectrolyte complexation with SA.

[0045] As an embodiment of the present application, the polylactic acid PLA modification process comprises the following steps: select low molecular weight PLA (such as PLA2002D), dissolve in dichloromethane (concentration 5-8% w / v), and add 10% polyethylene glycol (PEG 400) as a plasticizer.

[0046] As an embodiment of the present application, different mass ratios of SA, CS, and PLA are selected, mixed in the above solution, and a stable emulsion is formed by high-pressure homogenization. In this embodiment, the microcapsules are required to rupture in three months, so the ratio of SA, CS, and PLA is selected to be 5:2:3.

[0047] As an embodiment of the present application, a coaxial needle is used, with an inner needle of 0.5-0.8 mm (core material electrolyte) and an outer needle of 1.0-1.5 mm (wall material solution), and the total diameter is controlled by double-layer wrapping. The electrolyte flow rate is controlled at 10-15 μL / min (to ensure that the core material volume accounts for about 30%, avoiding capsule diameter exceeding the limit); the wall material solution flow rate is controlled at 20-30 μL / min. The electrostatic field parameters are: voltage 20-25 kV, plate spacing 10-15 cm, and droplet forming frequency 50-100 Hz.

[0048] As an embodiment of the present application, the wall material needs to be solidified after the capsule is formed. First, the droplet is dropped into a solidification liquid containing 2% CaCl2 (containing 0.1M NaCl, 0.1% and pH=5 chitosan), at which time Ca 2+ Cross-linking with the carboxylate of SA forms a gel network, and hydrogen bonding and electrostatic interaction enhance the compactness of CS and SA, and solidification is completed after 30 minutes.

[0049] After filtration, the capsules were transferred to a vacuum drying oven at 40°C to evaporate the dichloromethane solvent for 2 hours to form a dense hydrophobic layer.

[0050] As a specific embodiment of the present application, the microcapsule forming device was set with the following parameters: inner needle 0.7 mm for electrolyte, outer needle 1.2 mm for wall material, electrolyte flow rate 15 μL / min, wall material solution flow rate 27 μL / min, voltage 23 kV, plate spacing 14 cm, and droplet forming frequency 70 Hz.

[0051] The wall thickness was controlled at 20 μm, the capsule diameter was 600 μm, and the volume of a single capsule was calculated to be 0.0875 mm 3 , containing about 0.910 mg of 1Mol / L KOH electrolyte, and the total mass of the capsule was about 1.038 mg.

[0052] A No. 5 nickel-hydrogen battery with a capacity of 1500 mAh was prepared, and 2.30 g of 8Mol / L KOH electrolyte was added, and 100 microcapsules were added, a total of about 103.8 mg.

[0053] The same parameters as in the example were used to prepare the comparative example.

[0054] Comparative Example 1

[0055] The microcapsule forming device was set with the following parameters: inner needle 0.5 mm for electrolyte, outer needle 1.2 mm for wall material, electrolyte flow rate 14 μL / min, wall material solution flow rate 26 μL / min, voltage 23 kV, plate spacing 14 cm, and droplet forming frequency 70 Hz.

[0056] A No. 5 nickel-hydrogen battery with a capacity of 1500 mAh was prepared, and 2.30 g of 8Mol / L electrolyte was added, and 91 mg of 1mol / L electrolyte was added.

[0057] Comparative Example 2

[0058] The microcapsule forming device was set with the following parameters: inner needle 0.5 mm for electrolyte, outer needle 1.2 mm for wall material, electrolyte flow rate 14 μL / min, wall material solution flow rate 26 μL / min, voltage 23 kV, plate spacing 14 cm, and droplet forming frequency 70 Hz.

[0059] A No. 5 nickel-hydrogen battery with a capacity of 1500 mAh was prepared, and 2.30 g of 8Mol / L electrolyte was added, and 91 mg of 8mol / L electrolyte was added.

[0060] Comparative Example 3

[0061] The parameters of the microcapsule forming device are set as follows: the inner needle is 0.5 mm for electrolyte, the outer needle is 1.2 mm for wall material, the flow rate of electrolyte is 14 μL / min, the flow rate of wall material solution is 26 μL / min, the voltage is 23 kV, the distance between the plates is 14 cm, and the droplet forming frequency is 70 Hz.

[0062] A No. 5 nickel-hydrogen battery with a capacity of 1500 mAh is prepared, and the amount of 8Mol / L electrolyte added is 2.30 g.

[0063] The nickel-hydrogen battery prepared in the application and the nickel-hydrogen battery prepared in the comparative example are tested, and the test results are as follows:

[0064]

[0065]

[0066] The main functions of the application are:

[0067] (1) Controllable timed release: By adjusting the ratio of sodium alginate: chitosan: polylactic acid and the wall thickness, microcapsules with a rupture time ranging from 1 month to 1 year can be designed, realizing the "internal liquid supplement" in the middle period of battery use;

[0068] (2) Significantly prolonging the cycle life: After adding the microcapsules in a 1500 mAh nickel-hydrogen secondary battery, the number of cycles to 80% remaining capacity can be increased from ≤285 times to ≥330 times, with a life improvement of about 12%-30%;

[0069] (3) Inhibiting the increase of internal resistance: The internal resistance of a conventional liquid-poor battery increases by about 35% after 200 cycles; the microcapsule group of the application only increases by ≤20%, effectively improving the voltage drop and energy loss during high-rate discharge;

[0070] (4) Excellent stability in alkaline environment: The PLA skeleton is resistant to alkali and corrosion, the SA / CS network is not easy to swell or crack, and it does not interfere with the electrolyte, ensuring the chemical stability during long-term storage and use;

[0071] (5) CaCl2 crosslinking, simple and controllable vacuum drying process, good uniformity of particle size (400-600 μm) and wall thickness, easy to mass produce and controllable cost;

[0072] (6) CS crosslinking reinforces the capsule wall, the microcapsules are not easy to break during transportation, assembly and loading into the battery, ensuring that the liquid supplement function is only activated at the predetermined time;

[0073] (7) Triggered release does not require high temperature or chemical reagents, only relies on the degradation of the capsule wall itself or weak pH / humidity changes; eliminates the risk of organic solvent leakage and thermal runaway;

[0074] (8) Through material matching, curing conditions and particle size adjustment, the liquid supplementing period and rate can be customized for different types (nickel-hydrogen, nickel-cadmium, nickel-zinc, etc.) and different use environments (temperature, humidity, altitude), and the existing battery structure is compatible;

[0075] (9) Various rupture triggering modes such as temperature sensitivity, pH response and magnetic field remote control can be realized to meet different maintenance and remote liquid supplementing needs.

[0076] In summary, after reading the present application document, the person skilled in the art can make other various corresponding transformation schemes according to the technical solutions and technical concepts of the present application without creative mental effort, which all belong to the scope protected by the present application.

Claims

1. A controllable rupture alkaline electrolyte microcapsule, characterized in that: The controllable rupture type alkaline electrolyte microcapsule comprises: Capsule core: the content is alkaline electrolyte; Capsule wall: composed of sodium alginate, chitosan and polylactic acid, with the mass fraction of sodium alginate being 30-70wt%, chitosan being 10-30wt%, and polylactic acid being 20-50wt%. The capsule wall thickness is 15-25μm, and the microcapsule diameter is 400-600μm.

2. The controllable rupture alkaline electrolyte microcapsule according to claim 1, characterized in that: The composite ratio of the sodium alginate, chitosan and polylactic acid is 8:2:2 to 3:2:

7.

3. The controllable rupture alkaline electrolyte microcapsule according to claim 2, characterized in that: The composite ratio of sodium alginate, chitosan and polylactic acid is 5:2:

3.

4. A method for preparing a controllable rupture type alkaline electrolyte microcapsule according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Prepare sodium alginate SA solution and chitosan CS solution to modify polylactic acid PLA; S2: Prepare a mixed solution of SA, CS, and PLA, and inject the electrolyte and wall material into the mixed solution simultaneously using a high-pressure microencapsulation machine; S3: drop the liquid into a 2% CaCl2 solidification solution and solidify for 30 minutes; S4: After filtration, the capsules were transferred to a vacuum drying oven for 2 hours.

5. The method for preparing a controllable rupture type alkaline electrolyte microcapsule according to claim 4, characterized in that: The SA solution preparation comprises the following steps: Sodium alginate was dissolved in deionized water at a concentration of 2-5% w / v and stirred magnetically until completely dissolved; 0.5-1% sodium citrate was added.

6. The method for preparing a controllable rupture type alkaline electrolyte microcapsule according to claim 4, characterized in that: The CS solution preparation comprises the following steps: CS was dissolved in 1% acetic acid solution to a concentration of 2-4% w / v, and 0.1% polysorbate 80 was added.

7. The method for preparing a controllable rupture type alkaline electrolyte microcapsule according to claim 4, characterized in that: The polylactic acid (PLA) modification process comprises the following steps: Low molecular weight PLA was selected and dissolved in dichloromethane with a concentration of 5-8% w / v, and 10% polyethylene glycol was added.

8. The method for preparing a controllable rupture type alkaline electrolyte microcapsule according to claim 4, characterized in that: The CaCl2 solidification liquid in step S4 contains 0.1M NaCl and 0.1% chitosan with a pH of 5.

9. The method for preparing a controllable rupture type alkaline electrolyte microcapsule according to claim 4, characterized in that: In step S2, the inner needle of the high-voltage microcapsule embedding machine is 0.5-0.8 mm, the outer needle is 1.0-1.5 mm, the electrolyte flow rate is controlled to be 10-15 μL / min, the wall material solution flow rate is controlled to be 20-30 μL / min, the voltage is 20-25 kV, the plate spacing is 10-15 cm, and the droplet forming frequency is 50-100 Hz.

10. The method for preparing controllable rupture alkaline electrolyte microcapsules according to claim 9, characterized in that: In step S2, the inner needle of the high-voltage microcapsule embedding machine is 0.5 mm for the electrolyte, the outer needle is 1.2 mm for the wall material, the electrolyte flow rate is 14 μL / min, the wall material solution flow rate is 26 μL / min, the voltage is 23 kV, the plate spacing is 14 cm, and the droplet forming frequency is 70 Hz.

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