Function And Safety Guide Of Zinc Battery

1. Working principle of zinc battery
2. Opportunities and challenges of zinc battery
3. Improvement of energy density and power density
4. Verification of biological safety of zinc battery
5. Summary

Energy storage devices are the main part of biocompatible electronic products in terms of size, weight, volume and service life, so the requirements for biosafety and reliability are very high. Secondary battery play an indispensable role in energy storage and power supply.

Among them, zinc battery, as one of the strong competitors of lithium battery, have many advantages and safety advantages when used in biocompatible electronic devices. Currently, energy storage systems commonly used in biocompatible electronics include lithium battery and capacitors, among others.

Capacitors can provide excellent rate performance and cycle stability, but their biggest problems are low energy density and energy efficiency. Compared with other battery cells and capacitors, zinc battery have attracted attention in recent years because of their good safety, low cost, high capacity, and better energy density.

Furthermore, the flexible and safe components (hydrogel electrolyte and various flexible current collectors) make Zn battery more competitive for biocompatible electronics.

Working principle of zinc battery

Zinc battery based on metallic Zn anodes have attracted extensive attention in recent years. Emerging zinc-based battery systems include zinc-air battery (ZABs), zinc-metal battery (ZMBs), zinc-ion battery (ZIBs), and battery based on other conversion reactions, such as zinc-iodine battery, zinc-bromine battery, and two-electron zinc-manganese battery.

Zinc battery research generally uses button battery. However, limited by the liquid electrolyte and the rigid stainless steel case, this configuration does not meet the design principles of biocompatible zinc battery. Therefore, substantial efforts have been devoted to developing flexible structural designs relying on novel fabrication techniques and research on hydrogel electrolytes.

This article summarizes the research progress and corresponding advantages and disadvantages of various wearable battery configurations. Among them, the reported configurations of wearable zinc battery can be divided into planar structure and cable structure.

Opportunities and challenges of zinc battery

Despite the unique advantages of biocompatible Zn battery for use in wearable and implantable electronics, there are still issues related to engineering design and Zn battery electrochemistry for practical applications. Dendrite growth during cycling is one of the major problems of Zn battery when Zn metal is used as the anode.

However, this issue has been little studied in flexible Zn battery. In fact, the growth of Zn dendrites in flexible configurations may be more severe due to the extremely uneven electric field distribution.

Packaging materials are one of the main battery materials, and there is no consensus on suitable packaging materials for biocompatible battery. Generally speaking, biocompatible battery should require stretchable and tough packaging materials to prevent damage to the packaging from causing electrolyte and current leakage and damaging human tissue.

In addition, considering the large-scale transportation and assembly process in practical applications, gel dehydration and large-scale assembly processes must also be considered.

Improvement of energy density and power density

In biocompatible zinc battery, due to the low ionic conductivity of hydrogel electrolytes and poor contact between electrodes and electrolytes, the battery performance is limited by large battery impedance, poor rate capability, and low energy density. In addition, the excessive use of zinc metal will increase the overall weight of the battery and aggravate side reactions.

In response to the above problems, researchers have proposed some optimization strategies, such as introducing graphene oxide into the gel, to improve the ionic conductivity of the hydrogel electrolyte by promoting ion transport. In battery applications, bending can sometimes cause the interface to slip, resulting in a loss of contact between the electrolyte and the electrodes.

Therefore, it is of great significance to employ viscous hydrogels when designing biocompatible battery. The use of negative electrode current collector is a feasible measure to solve the cost increase and side reaction intensification caused by the excessive use of zinc metal. In addition, the use of current collectors can improve the utilization of active materials, leading to higher energy densities.

Verification of biological safety of zinc battery

Biocompatible zinc battery are designed for devices close to the human body, especially for implantable battery. Therefore, reasonable validation and rigorous evaluation must be performed before use in humans.

In general, the design and use of biocompatible zinc battery should follow the following procedures: rational material and structure design, precise device assembly, strict animal experiments, and practical applications.

When the battery needs to work in the body for a long time, the stability (cycle stability and in vivo stability) needs to be reconsidered. The in vivo stability indicates that the implantation of the device will not trigger an immune response, and the battery can work stably in the body. Cycling stability ensures that the battery provides stable and sufficient energy for the device.

• Focus on the matrix material of the hydrogel electrolyte

As one of the essential components in biocompatible zinc battery, the research on hydrogels should not only focus on the modification of electrolyte solute components and additives, but more attention should be paid to designing them with high conductivity, flexibility and viscosity.

• Reasonable design of current collector

In order to achieve flexibility and improve the electronic conductivity of the electrode, both the positive and negative electrodes of the biocompatible zinc battery can use current collectors. Therefore, optimization of the material and structure of the current collector should be considered.

• More systematic performance evaluation

Differences in the flexibility evaluation criteria for biocompatible battery hinder performance comparisons between different battery. The article proposes to use parameters to describe the bending state of flexible battery in order to establish a unified test standard.

• Strict biocompatibility verification

For devices that are used close to the human body, especially implantable devices, safety and stability should be considered at the same time, and animal experiments should be verified in advance. It should be noted that stability should not only be characterized by cycle stability, in vivo stability may be more important for semi-permanent implantable devices.

• Integrate with various devices

The coupling of biocompatible Zn battery to target devices should be paid attention to, but little research in this area hinders the commercialization process. In fact, more problems can arise in getting the different parts to work in harmony, so they need to be thought out in advance.

Summary

As an emerging low-cost device energy technology, the development of biocompatible zinc battery is still at an early stage. Unremitting efforts on the basis of zinc battery research will provide a broader prospect for the study of biocompatible zinc battery with flexibility, biosafety and better electrochemical performance. The views and insights contained in this review may help to better coordinate further research to develop biocompatible zinc battery.

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