CN115295930B - Hollow structure solid-state zinc-air battery with integrability - Google Patents

Abstract

The invention is inspired by the bionic thought, and innovates the solid zinc-air battery from two aspects of solid electrolyte and battery structure by taking reference to the chemical structure of the biosurfactant in alveoli and the characteristic that the respiratory system of animals is positioned in the body. On one hand, the surface of the hydrogel is modified with a surfactant with a gemini structure, so that the moisture retention of the solid electrolyte and the cycling stability of the battery are greatly improved. On the other hand, a solid zinc-air battery with a columnar hollow structural feature is designed, wherein an air electrode is built in the solid zinc-air battery. The structural design provides for higher integration of the solid zinc-air battery. The plurality of cells can be arranged in parallel and bundled into a compact battery pack. The solid zinc-air battery is expected to be used as a high-safety green power supply to be applied to household appliances, portable devices, intelligent robots and future devices combined with human bodies.

Description

Hollow structure solid-state zinc-air battery with integrability

Technical Field

The present invention belongs to the field of new solid-state batteries. Inspired by the bionic idea, innovations have been made in the two aspects of solid electrolyte and battery structure design, so that the solid-state zinc-air battery has a more stable cycle performance and its structure has more practical value. It is convenient to integrate into a large battery pack, effectively alleviate the problems of seepage and air electrode surface contamination, effectively improve the stability of the solid electrolyte, and greatly improve the cycle life of the battery. This type of solid-state zinc-air battery is expected to be used as a high-safety battery in household or portable devices, intelligent robots, and future devices combined with the human body.

Background Art

Rechargeable zinc-air batteries (ZABs) are considered to be strong competitors for new power batteries due to their low cost, high theoretical energy density (1084Wh kg ^-1 ), high safety, and pollution-free. Recently developed solid-state zinc-air batteries have attracted increasing attention due to their flexible and diverse device types, especially their obvious advantages in device miniaturization compared with liquid zinc-air batteries. At present, a large number of studies are still focused on the electrocatalysts of air electrodes, although battery performance may be mainly limited by the stability of gel electrolytes or zinc electrodes. Recently, an Ah-class solid-state zinc-air battery was reported in Nature Energy, which has been able to stably charge and discharge for more than 6000 cycles (Nature Energy, 6 (2021) 592-604.). This indicates that solid-state zinc-air batteries are expected to be put into practical application. However, the current solid-state zinc-air batteries are still in the development stage, and there are many unreasonable factors that limit their commercialization process.

For example, the types of polymers used in the solid electrolytes reported in the current articles are still relatively small, mainly including polyvinyl alcohol (PVA), polyacrylic acid (PAA) and polyacrylamide (PAM). Among them, PVA has a good industrialization foundation. PVA products of various molecular weights have been commercialized with relatively fixed specifications. Battery companies can purchase them according to the brand. PVA has good water solubility, excellent film-forming properties and electrochemical stability, and is very suitable for developing solid gel electrolytes for zinc-air batteries as a matrix. PVA-KOH gel has high ionic conductivity and can meet the needs of zinc-air batteries. It is a common solid gel electrolyte in the literature. However, since zinc-air batteries need to expose their air electrode parts to the air, the electrolyte is prone to dehydration due to the decrease in air humidity. This situation has a significant impact on PVA-KOH gel electrolytes. Therefore, the cycle performance of solid zinc-air batteries using PVA-KOH gel is often seriously affected by this problem. In order to improve the performance, the literature uses various additives to form a composite gel electrolyte when preparing PVA-KOH gel. For example, the literature reports that adding SiO ₂ or cellulose to PAV gel can improve the stability of the solid electrolyte, thereby improving its cycle performance. Fan et al., by adding SiO ₂ to PVA gel, extended the charge and discharge cycle time of the solid-state zinc-air battery to 48 hours (Nano Energy, 56 (2019) 454-462). Zhao et al., by adding bacterial cellulose to PVA gel, significantly extended the charge and discharge cycle time of the solid-state zinc-air battery (ACS Applied Materials & Interfaces, 11 (2019) 15537-15542).

On the other hand, the structural design of solid-state zinc-air batteries also has a lot of room for improvement. The flat-type and cable-type solid-state zinc-air batteries reported so far all use a design in which the air electrode directly faces the atmosphere. Although this design is conducive to reflecting the flexibility of the battery, it actually hinders the commercialization of solid-state zinc-air batteries. In actual use, the air electrodes of batteries with these structures are very easy to lose water due to air flow, easy to seep liquid, and easy to be contaminated by dust. On the other hand, these zinc-air batteries have low integrability and are not suitable for large-scale integration in compact spaces. They can only drive some very low-power devices. Therefore, the solid-state zinc-air batteries reported so far are not practical in terms of device structure.

Summary of the invention

The present invention is inspired by the bionics idea and learns from the structural characteristics of the respiratory system of animals to improve the performance of solid-state zinc-air batteries. According to medical research, the surface of human alveoli contains a layer of biosurfactant that can protect alveolar function. This biosurfactant is dipalmitoyl lecithin, a lecithin with a Gemini structure. This lecithin molecule is arranged vertically at the liquid-gas interface, which plays an important role in reducing alveolar surface tension, maintaining alveolar volume stability, and preventing tissue fluid exudation. In addition, the respiratory system of animals is hidden in the body, rather than directly exposed to the air, which effectively prevents the drying of the alveoli and dust pollution. Inspired by the characteristics of the respiratory system of these animals, the present invention has made innovations in two aspects: solid electrolyte and battery structure design.

1. Modify the surface of PVA gel with a twin-structure surfactant molecule. It is found that the modified PVA-KOH gel has higher water retention, better dimensional stability and more stable ionic conductivity. This significantly improves the charge and discharge cycle stability of the solid-state zinc-air battery.

2. On the other hand, the present invention designs a new structure of solid-state zinc-air battery, which adopts a cylindrical hollow structure and embeds the air electrode. This allows the new structure of solid-state zinc-air battery to be easily integrated into a compact battery pack to drive larger devices. This strategy of embedding the air battery effectively reduces the problem of air flow drying the air electrode, and can effectively alleviate the problems of battery leakage and prevent air electrode contamination. This battery structure improves the charge and discharge cycle stability of the battery.

3. The columnar electric field inside the battery may be beneficial to improving the charging and discharging stability of the battery, and obtaining a high charging and discharging cycle stability. The present invention is characterized in that:

1. Apply bionic ideas to the preparation of solid electrolytes and battery structure design in zinc-air batteries. Mainly drawing on the structure of human alveolar surfactant and the built-in characteristics of animal respiratory systems.

2. A molecular protective film is formed on the surface of the gel electrolyte by using a Gemini surfactant, which effectively improves the water retention rate of the solid electrolyte and the stability of the electrolyte without affecting the ionic conductivity. The method is to soak the PVA gel (or a mixed hydrogel of PVA and PAA) in a solution of a Gemini surfactant. Among them, the Gemini surfactant used is lecithin or Surfynol surfactant (Chinese name: 2,4,7,9-Tetramethyl-5-decyne-4,7-diol polyoxyethylene ether, English name: 2,4,7,9-Tetramethyl-5-decyne-4,7-diol ethoxylate), and the mass concentration range in the soaking solution is 0.5-5%. In addition to the surfactant, potassium hydroxide (KOH) and zinc acetate are also added to the soaking solution.

3. The structure of the solid-state zinc-air battery adopts a unique design, with the air electrode built in. From the inside to the outside, its structure consists of a porous inner tube (referred to as: air inner tube), air electrode, solid electrolyte, metal zinc electrode, and battery packaging shell.

4. The cylindrical hollow structure design gives the solid-state zinc-air battery higher integration. Multiple batteries can be arranged in parallel and bundled together, and then connected in series and parallel to form a compact battery pack to power external devices.

5. This battery structure can effectively alleviate the pollution problem caused by direct contact between the air electrode and the atmosphere. In addition to using an open method to exchange gas with the air, the air inner tube can also be connected by a pipeline and oxygen can be introduced to achieve operation in a closed system.

The advantages of the present invention are:

1. By modifying the surface of PVA-KOH gel with a surfactant with a twin structure, the water retention rate of the gel electrolyte is effectively improved, the dimensional stability of the gel electrolyte is significantly improved, and the ionic conductivity is more stable; the cycle life of the solid-state zinc-air battery is significantly improved.

2. The unique design of built-in air electrode gives the solid-state zinc-air battery high integration. This battery design can effectively alleviate the problem of liquid seepage; it can effectively avoid the pollution problem of air electrode and reduce the probability of air dust covering the air electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of the appearance of a single cell

Figure 2 is a schematic diagram of the internal structure of a single cell

Figure 3 is a schematic diagram of the general structure of the air inner tube

Figure 4 is a schematic diagram of the general shape of the air electrode

Figure 5 is a schematic diagram of the general shape of the zinc electrode

Figure 6 is a schematic diagram of the general shape of the solid electrolyte

Figure 7 is a schematic diagram of a 3×3 series-parallel battery pack

Figure 8 is a schematic diagram of a 3×3 series battery pack

Figure 9 is a photo of a solid-state zinc-air battery

Figure 10 is a photo of a 3×3 solid-state zinc-air battery pack driving a lighting stick

Figure numerals: (1) zinc electrode (2) solid electrolyte (3) air electrode (4) air inner tube (5) packaging shell.

DETAILED DESCRIPTION

The present invention will be further described in detail below with reference to the accompanying drawings.

1. Design description of cylindrical hollow zinc-air battery

The appearance of a single cell of a cylindrical hollow zinc-air battery is shown in Figure 1, which is a schematic diagram of the appearance structure of a single battery after packaging. The entire battery is a cylindrical hollow structure. In the middle is an air inner tube, which can provide a gas exchange path for the air electrode. The positive and negative pole ears are located on both sides of the air inner tube, and their interiors are connected to the air electrode current collector and the zinc electrode current collector respectively.

Attached Figure 2 shows the internal structure of this solid-state zinc-air battery. The numbers in the figure are: (1) zinc electrode (2) solid electrolyte (3) air electrode (4) air inner tube (5) packaging shell. The structure of the battery from the inside to the outside is air inner tube, air electrode, solid electrolyte, metal zinc foil, and packaging shell. Among them, many holes are pre-punched on the air inner tube to facilitate gas exchange, the air electrode can be a structure in which carbon cloth loaded with oxygen catalyst is bonded with a nickel mesh (the nickel mesh is used as a current collector on the side close to the air inner tube), and the packaging shell can be a heat shrink tube (such as a traditional battery heat shrink film or plastic heat shrink tube). Two partially enlarged structural schematic diagrams (A and B illustrations in Attached Figure 2) respectively show the internal structure of the connection between the positive and negative pole ears. Through reasonable size and local design, both structural compactness and short circuit problems are avoided.

Figure 3 shows a schematic diagram of the structure of the inner air tube. The inner air tube can be made of various high-strength materials, such as acrylic tubes, PVC tubes, carbon fiber tubes or other plastic materials. There are many holes distributed on the tube wall, mainly to provide gas channels for the air electrode. The size of the holes is distributed in alternating combinations of two different sizes, which can ensure sufficient gas exchange area and sufficient mechanical strength of the tube wall.

Attached Figures 4 and 5 show schematic diagrams of the shapes of the air electrode and the zinc foil electrode, respectively. They are both cut into a design of an integrated electrode with a tab strip and a square electrode. The air electrode in Attached Figure 4 is made of a nickel mesh and a gas diffusion layer bonded together, and a bifunctional oxygen electrode catalyst is loaded on the gas diffusion layer. Attached Figure 5 uses zinc foil or galvanized metal foil.

6 shows a schematic diagram of the shape of the solid gel electrolyte. From the front view and the top view, it can be seen that the side edges are beveled to facilitate seamless contact at the interface when the battery is rolled up after assembly (as shown in the schematic diagram of the rolled state in FIG6 ).

Figures 7 and 8 provide schematic diagrams of a 3×3 battery pack integrated with 9 cells, as well as wiring diagrams for parallel (Figure 8) and series (Figure 9). The design of built-in air electrodes allows these cells to be assembled in parallel to form larger battery packs. Based on the strategy of this schematic diagram, the scale of integration can be further expanded to form a larger number of battery integrations to achieve large battery pack modules.

2. Preparation of solid electrolyte

Preparation example 1 of solid electrolyte:

Preparation of PVA gel electrolyte modified with lecithin gemini surfactant: 4 g of PVA powder was slowly dissolved in 40 mL of deionized water and stirred at 95 °C for 2 hours. The resulting solution was poured into a square container and frozen at -20 °C for 12 hours to obtain PVA gel. 0.25 g of lecithin was added to 40 mL of a solution containing 6 M KOH and 0.2 M zinc acetate and stirred to form a uniform dispersion. Then, the thawed PVA gel was immersed in the dispersion and shaken on a shaker for 24 hours to obtain a solid electrolyte.

Preparation example 2 of solid electrolyte:

Preparation of PVA/PAA mixed gel electrolyte modified by Surfynol Gemini surfactant: 3g PVA powder and 1g PAA powder were slowly dissolved in 40mL deionized water and stirred at 95°C for 2 hours. The resulting solution was poured into a square container and frozen at -20°C for 12 hours to obtain PVA gel. 0.25g Surfynol surfactant (purchased from Air Products and Chemicals, Inc.) was added to 40mL of a solution containing 6M KOH and 0.2M zinc acetate and stirred to form a uniform dispersion. Then, the thawed PVA/PAA mixed gel was immersed in the dispersion and shaken on a shaker for 24 hours to obtain a solid electrolyte.

3. Battery assembly and integration

Zinc-air battery cell assembly: stack the cut zinc foil, solid electrolyte, and air electrode in sequence. Place the air inner tube in between and use it to roll up the electrode stack. After fixing with tape, place the cell in a heat shrink tube and heat shrink it. If necessary, use solid sealant to locally treat the gap.

Integration of zinc-air batteries: Nine zinc-air battery cells can be arranged as shown in Figures 7-8, and then tied together with tape, rolled strips or heat shrink film to form a 3×3 battery pack. Then, the positive and negative pole ears are connected in parallel according to Figure 7 to obtain a battery pack module with a voltage of 3-5V, or connected in series according to Figure 8 to obtain a battery pack module with an output voltage of 10-15V. It should be noted that the zinc-air battery of this structure can not only be integrated into a 3×3 battery pack module, but also integrated into a larger battery pack as needed.

In addition, it should be pointed out that the air inner tube of the zinc-air battery can be used not only in an open manner to exchange gas with the air; but also by connecting all the air inner tubes with pipes and introducing oxygen to achieve operation in a closed system.

4. Battery performance

The test results of a single cell of this type of cylindrical hollow zinc-air battery are as follows:

The test results of the battery using lecithin-modified PVA gel electrolyte are as follows: the maximum output power density is 50mW/ ^cm2 , the open circuit voltage is 1.35V, and the repeated charge and discharge cycle (at a rate of 2mA/ ^cm2 , charging for 10 minutes/discharging for 10 minutes alternately) can reach 100 hours and 300 cycles.

The test results of the battery using the Surfynol-modified PVA/PAA mixed gel electrolyte are as follows: the maximum output power density is 55mW/ ^cm2 , the open circuit voltage is 1.33V, and the repeated charge and discharge cycle can reach 120 hours and 360 cycles.

In contrast, the test results of the battery using unmodified PVA gel electrolyte are: the maximum output power density is 50mW/ ^cm2 , the open circuit voltage is 1.32V, and the repeated charge and discharge can only cycle for 10 hours, 30 cycles.

Claims (4)

1. A solid-state zinc-air battery designed based on bionics, which draws on the chemical structure of alveolar surfactant and the characteristics of animals placing their respiratory systems in their bodies, and is characterized by: (1) the overall design of the battery adopts a cylindrical hollow structure with an air electrode built in, and from the inside to the outside are a porous inner tube, an air electrode, a solid electrolyte, a zinc electrode, and a packaging shell; (2) the solid electrolyte is a gemini surfactant modified on the surface of a polymer hydrogel to improve the performance of the solid electrolyte; the surface-modified gemini surfactant is lecithin or 2,4,7,9-tetramethyl-5-decyne-4,7-diol polyoxyethylene ether, and the mass concentration range in the soaking solution is 0.5-5%; in addition to the surfactant, potassium hydroxide (KOH) and zinc acetate are added to the soaking solution; the modification process is to soak the polymer gel in a solution containing the surfactant for 10-24 hours; (3) the polymer hydrogel is a polyvinyl alcohol gel or a mixed hydrogel of polyvinyl alcohol and polyacrylic acid; (4) the solid-state zinc-air battery can be combined with each other to form a battery pack as needed. 2. In the solid-state zinc-air battery designed based on the bionic concept as described in claim 1, the holes on the wall of the porous inner tube are arranged in an alternating manner of large holes and small holes to ensure gas exchange while also ensuring the mechanical strength of the tube. 3. The solid-state zinc-air battery designed based on the bionic concept according to claim 1, wherein the shape of the solid electrolyte is characterized by a beveled cut on the side to ensure that the two sides of the solid electrolyte can be seamlessly connected when the cylindrical battery is assembled. 4. Based on the solid-state zinc-air battery designed based on the bionic concept described in claim 1, multiple batteries can be arranged side by side or bundled to form a battery pack as needed.