"Bionic Skin" Calms The "chaos" On The Surface Of Metal Electrodes-Qiming Carbon

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"Bionic Skin" Calms The "chaos" On The Surface Of Metal Electrodes

May,21,2023

Schematic diagram of human skin.

■Our reporter Wang Haohao

Electrolytes in chemical batteries contain raw materials such as solvents and solutes. If the metal electrode surface of the battery is not well protected, the electrolyte will continue to decompose during the charging and discharging process, and dendrites will grow on the surface. The "twigs" can pierce the battery diaphragm, causing the battery to short-circuit and fail.

Researchers have been looking for ways to protect the surfaces of metal electrodes to extend the cycle life of batteries and improve overall performance. The team of Professor Lu Bingan of Hunan University and the team of Professor Wang Chengxin of Sun Yat-sen University jointly developed a metal electrode skin (MES) that simulates human skin, which can stabilize the metal interface well. Recently, this result was published in -.

Take inspiration from human skin

The metal anode is an ideal anode material for high-energy-density batteries, but it exhibits extremely high reactivity, and it is easy to form an unstable solid-electrolyte interface after contact with the electrolyte, and the plating/stripping morphology cannot be controlled during charge and discharge, resulting in Metallic dendrite growth. These problems will lead to a decrease in the Coulombic efficiency of the battery or even a short circuit, thereby causing safety issues.

Graphite electrode_use graphite as electrode, electrolyze copper chloride and sodium chloride_porous graphene electrode

"The industry has been looking for the best solution to protect the metal anode interface." Ding Hongbo, the first author of the paper and a doctoral student in the School of Physics and Microelectronics Science of Hunan University, introduced that to prevent the growth of dendrites on the surface of the metal anode, Lu Bing'an's team has successively developed The three-dimensional material, based on it, deposits metal ions into the interior rather than the surface so that dendrites do not form on the surface. This research has greatly improved the cycle stability and life of potassium metal batteries, but the three-dimensional host will increase the mass of the metal electrode and affect the energy density of the battery, and the pure three-dimensional host cannot improve the stability of the battery. metal interface.

The skin is the largest organ of the human body, covering the body's surface and in direct contact with the external environment. The skin is divided into the epidermis and dermis. The epidermis is located on the surface of the skin and primarily serves as a barrier against mechanical, physical, chemical, and microbial damage. The dermis makes the skin more malleable and elastic.

In the process of continuous experimentation, the researchers suddenly had an idea: "Can the unique structure and characteristics of human skin be applied to the protection of metal electrodes?"

Potassium metal batteries possess low redox potential and high theoretical capacity, properties that make them considered one of the most promising candidates for next-generation energy storage devices. Potassium metal has a higher energy density than disclosed anode materials for potassium-ion batteries.

Inspired by the structure and function of human skin, the research team built a skin-like biomimetic protective layer on the surface of potassium metal, hoping to protect the metal electrode by improving interface stability and inhibiting dendrite growth.

They transferred fluorine-doped graphene oxide onto copper foil through a simple and efficient process and then used a roller press to transfer the material to the surface of potassium metal. The results show that the MES has a high surface flatness, which can control the surface electric field intensity of the initial cycle. A uniform electric field affects the concentration of ions, making them evenly deposited on the electrode surface.

graphite electrode_porous graphene electrode_use graphite as electrode, electrolyze copper chloride and sodium chloride

To further illustrate the effect of surface flatness on metal plating, the research team studied the effect of surface flatness on the potential distribution and potassium ion deposition morphology through simulations. The results show that the MES coverage greatly enhances the uniformity of the surface field strength, and the distribution of potassium ions near the surface is also more uniform.

"This means that MES can increase the flatness and uniform electric field distribution of the electrode, and can inhibit the growth of dendrites." Hongbo Ding said.

Similar to how the dermis and epidermis of human skin protect the inner cells and muscles, the graphene layer on the potassium metal surface and the in situ reinforced solid electrolyte interfacial layer can effectively protect the metal anode.

To explore the in situ enhancement process at the solid-electrolyte interface in MES, the team performed computational studies using density functional theory. The study found that during the potassium deposition process, the carbon-fluorine bond in fluorine-containing graphene oxide will break and release fluorine element; the increase of fluorine content will form a fluorine-rich solid electrolyte interface on the surface, thereby improving the mechanical strength and stability of MES.

New 'skin' significantly extends battery life

How much can battery life be extended after dendrite suppression by MES?

use graphite as electrode, electrolysis Copper Chloride and Sodium Chloride_Graphite Electrode_Porous Graphene Electrode

The core material of MES is fluorine-doped graphene oxide. For the study, the team sonicated fluorine-doped graphene oxide in ethanol and dropped it on the surface of an aqueous solution. After multiple extractions, a film with a certain thickness is obtained. Repeated folding experiments show that this layer of the film has excellent metal fatigue properties, and the dried film can be rolled together with potassium foil to achieve large-scale preparation.

The research team tested the cycle life of the asymmetric battery composed of MES-modified copper foil at a current density of 0.5mA cm-2 and a capacity of 0.5mAh cm-2 and found that the plating/stripping life of the symmetric battery was only 2300 hours, and the asymmetric The cycle life of the battery reaches more than 3200 hours (1600 cycles). "This is one of the batteries with the longest cycle life of potassium-copper asymmetric batteries so far, which proves that MES can greatly improve the stability of the metal-electrode interface." Hongbo Ding said.

When paired with a Prussian blue cathode, the whole cell exhibits excellent rate performance and cycling stability (g-1, cycle life over 5000 cycles). Ding Hongbo said that the excellent performance and cycle stability indicate that MES has great potential in high-energy metal batteries, which may lay a solid foundation for next-generation battery-driven applications.

According to reports, this research provides a new way to design and manufacture new biomimetic metal electrode interfaces, and promotes multidisciplinary cooperation; a new metal electrode protection mechanism is proposed, which provides a new strategy for battery biomimetic applications.

The reviewers of the paper believe that this study develops a strategy to stabilize metal interfaces with MES that mimics human skin, which is very novel and creative. MES-protected metal electrodes extend the cycle life of symmetric and asymmetric batteries. The asymmetric potassium copper battery achieved more than 1600 cycles, which is one of the best potassium metal asymmetric batteries reported so far. The full cell also exhibits excellent performance and cycling stability.

"Overall, the bioinspired interface protection approach in this study is innovative, and the 'bionic' concept used in this work is an important enabler for future metal anode designs," said the reviewers.