Janus diaphragm for water-based zinc battery can hinder dendrites, extend battery life

　　Author ：Iflowpower – Постачальник портативних електростанцій

Janus is one of the most primitive gods in ancient Roman mythology. It is said that ancient Roman's coins are called this vision: Hold the door to open the door, hold the guard's cane. The legendary he has two faces, and each face symbolizes the status, start and end, the past and the future.

Through the door of the Yasause, means the state change. The ancient Romans will pray for Jasuus asylum when they started an important thing. This will be smooth.

In the development of modern materials science, Janus is used to refer to the design of two-phase structure and function, and scientists look forward to Janus design to achieve expected goals. For example, in the development of the diaphragm material of the secondary battery, JANUS design concept is often used. The main function of the diaphragm in the battery is to avoid physical contact between the positive electrode and the negative electrode, prevent overheating and explosion caused by short circuit generation of the battery.

To design the Janus diaphragm, the researchers usually practice a ceramic material or carbon material on the surface of the diaphragm to increase the safety of the secondary battery, but it will increase the overall quality and volume of the battery, and the energy density is sacrificed. Can not meet the requirements of lightweight and flexible wearable devices. Based on this problem, based on the preliminary research foundation, the direct growth of the vertical graphene of the ultra-thin layer is achieved by chemical vapor deposition techniques on the commercial glass fiber diaphragm, and the JANUS diaphragm is constructed without increasing the overall quality and volume of the device.

And applied to a flexible water-based zinc battery, hindering the formation of zinc negative dendrites, extending battery life. Related research results published on AdvanceDmaterials. The glass fiber encounters graphene-Janus diaphragms in recent years, wearable equipment market has developed rapidly, which combines the emerging field integrating artificial intelligence technology, flexible new material technology and portable energy technology into the development of science and technology.

Among them, the energy storage device is a key role in the development of the wearable device. Water-based zinc electricity is used as an electrolyte by water to avoid disadvantages of toxicity and flammability of organic electrolyte, which has broad prospects in the application of power supply in wearable equipment. The bottleneck currently hindering the large-scale application of the water-based zinc electrode is mainly due to poor electrochemical stability and lack of circulating life.

These problems mainly from the zinc metal negative electrode during cycle charge, especially under large current, easily grow raised zinc. Dendrits, thus thus puncture the glass fiber diaphragm that originally blocked, causing battery short circuit; in addition to the phenomenon of by-products and surface passivation generated by water decomposition. Although the diaphragm is often considered a non-active component in the battery, it is not involved in the battery reaction, but it also affects the performance of the water-based zinc electricity.

In general, the current research of diaphragm modification in the zinc electric sector is in the like. How to improve the safety of the battery through the optimal design of the fiberglass diaphragm? Our team has done a lot of exploration in the preparation of graphene on the glass substrate, and successfully achieves direct growth of graphene on glass fibers at lower temperatures. Combined with these preliminary foundations, we designed graphenes in a glass fiber as a three-dimensional conductive skeleton structure, and the other side still insulated the effect of the positive and negative electrode, so that JANUS diaphragm was prepared by graphene modification.

This design can be achieved in two aspects: one is that it can be regarded as an extended force of the zinc metal negative electrode, which can provide three-dimensional space for the deposition of zinc metals; the second is to reduce the local current density and the uniform distribution of the electric field, thereby suppressing the branch Crystal growth. In order to verify this guess, we contracted the effects of the Janus diaphragm and ordinary diaphragm on battery performance through conventional electrochemical test methods. We found that the battery using Janus diaphragm has a better cycle life.

It is also intuitively discovered that the Janus diaphragm is obtained by using an electron microscope and atomic force microscope. High security + long-range-zinc base storage system In order to better achieve the application of JANUS diaphragm in a zinc-based battery, it is critical. The preparation of the Janus diaphragm mainly involves two steps, and the Fresh graphite membrane is prepared by chemical vapor deposition (PECVD) in situ, and the second step is to prepare the final JANUS diaphragm by surface plasma.

Why do you have two steps? First, in the process of PECVD, some hydrocarbon-based contamination is produced on the surface of the diaphragm during the PECVD, resulting in difficulty in water electrolytes, so that these contaminants are removed by PLASMA. The infiltration of the electrolyte can be achieved well; note that this is a PLASMA treatment in an insulating surface of the Janus film, so it does not destroy the structure of thin layer graphene. Second, combined with the RAMAN and X-ray photoelectron energy spectroscopy (XPS) data can see more defects after PLASMA treatment, and also achieve the doping of graphene O elements and n elements.

From the results of finite element simulation analysis, the vertically grown graphene three-dimensional skeleton structure can effectively reduce the local current density, and then reduce the generation of dendrites, and the graphene skeleton can provide uniform distribution. Electric field, thus achieving uniform zinc deposition / stripping. Again, from the perspective of the atomic binding energy of zinc, the binding energy of the graphene and different heteroatom doped graphene on zinc is analyzed by density function, and the calculation results indicate the perfect graphene and zinc.

The binding can be poor, and the doping of the o, n element has a significant increase in zinc affinity, with the highest intracene binding energy of pyrrole nitrogen, which is also achieved with the presence of elemental analysis in the experiment. Mutual agreement. In order to verify the effect of the JANUS diaphragm in the zinc-based storage system, we use commercial activated carbon as a positive electrode material, the zinc sulfate solution is aqueous electrolyte, and the zinc ion mixed capacitor is assembled, which is expected to achieve high energy and high power.

Density synergy. In contrast, it was found that the zinc ion hybrid capacitor constructed by JANUS membrane further confirmed the electrochemical impedance analysis by electrochemical impedance analysis by electrochemical impedance analysis, which reduced charge transfer resistance and ion diffusion by electrochemical impedance analysis. Electrical resistance, improve Zn deposition kinetics.

At 5Ag-1 current density, 5000 cycles still have 93% capacity retention rate, which is much higher than the capacity retention ratio of 53% of the conventional separator. At the same time, we also build a zinc ion battery with battery material V2O5 as a positive electrode, realizing high energy density of 182WHKG-1, still 75% capacity retention ratio after 1000 cycles. In order to test its flexible performance, the flexible device is assembled using the Janus diaphragm and collects various bending angles of 30 ¡ã, 60 ¡ã, 90 ¡ã, and still has 97 when bent at 90 ¡ã.

8% capacity retention rate exhibits excellent mechanical flexibility. The V2O5 // Zn soft bag battery is assembled, and the LED can be lit through the series, which shows the potential of the wearable power supply as a portable electronic device. In summary, this effort is prepared by direct chemical vapor deposition techniques and Plasma treatment, thin graphene modified JANUS diaphragm is prepared by modifying the structure of the non-active components of the battery, and the improvement of the zinc metal negative electrode cycle stability is achieved, which in turn constructs Flexible water-based zinc ion batteries with more excellent electrochemical properties, bring broad prospects for future high performance, low-cost zinc battery.

At the same time, this strategy of this in situ modified diaphragm can also be used in other alkali metal batteries (Li, NA, K), with certain reference significance. With the improvement of battery safety, wearable equipment will also be more and more into our daily life. Chinese Science Bull.