All solid-state batteries welcome technological innovation: The University of Maryland team has prepared high energy density lithium sulfur batteries, which are expected to be used in battery products and electric vehicles and other fields

This is the last project of my doctoral program,For the first time in the world, fully solid-state oxide solid-state lithium-sulfur batteries have been achieved without the need to add any liquid electrolyte.This technology is a technological innovation in the field of solid-state batteries, and is based on the raw materials and preparation methods of the battery, which is conducive to the large-scale commercial production of this all solid-state battery A doctoral graduate from the University of Maryland in the United States.

Figure 1: Shi Changmin (Source:)

In recent decades, solid state lithium sulfur batteries have gradually developed, but there are still serious challenges to realize the "all" solid oxide solid electrolyte lithium sulfur batteries. The ultimate reason is that the sulfur positive electrode itself is insulated and the oxide solid electrolyte is very afraid of pressure and fragile, which can cause poor contact between the positive electrode and the electrolyte.

In previous studies, a small amount of liquid electrolyte needs to be added between the sulfur positive electrode and the garnet type oxide solid electrolyte oxide solid electrolyte (Li7La3Zr2O12, LLZO) to ensure good contact and lithium ion transport between the positive electrode and LLZO. Compared to traditional methods, all solid-state lithium sulfur batteries using LLZO are expected to achieve ultra-high energy density.

To improve the interface contact, ion and electron conduction of the solid-state cathode structure,A team from the University of Maryland in the United States has prepared an all solid-state garnet battery with a solid sulfur positive electrode. They have achieved the first all-solid-state lithium sulfur battery using LLZO solid electrolyte.

The key to successfully preparing an "all solid-state" lithium-sulfur battery this time is the discovery of a solid-state low melting point lithium salt. Moreover, all materials in all solid-state batteries, except for sulfur active substances, use inorganic materials, making sufficient preparations for the non combustible nature of the battery.

Solid low melting point lithium salts themselves have high ionic conductivity, which can reach 10-5S/cm at room temperature.Using this solid-state low melting point lithium salt, a high energy density all solid-state lithium sulfur battery has been achieved for the first time. It can stably cycle for 200 cycles at a high current density of 60 and maintain zero capacity decay.

The reviewer evaluated the technology and stated that it is a true solid-state battery made of very thin garnet electrolyte. Most of the work described in the literature uses thick particles and adds liquid on the cathode side to ensure system operation.

Figure 1 Related Papers (Source: ACSEnergyLetters)

Recently, the relevant paper was published in ACSEnergy Letters under the title of "All Solid State Garnet Type Sulfurized Polyacrylonitrile/Lithium Metal Batteries Implemented by Inorganic Lithium Salts and Double Layer Electrolyte Structures".

The doctoral graduates of the University of Maryland are the lead author of this paper, and Professor Eric D. Vauxman () of the University of Maryland is the corresponding author of this paper.

The first solid-state lithium sulfur battery to achieve high energy density

This study is the first to achieve an "all" solid-state lithium sulfur battery using oxide solid electrolytes, but it is not easy to embark on a new direction of research. In the initial stage of research, there was actually no great hope because no one had done it before.

Moreover, scientists generally believe that oxide solid-state lithium-sulfur batteries are "currently hopeless" because there are too many technical challenges to overcome compared to other battery systems.

But he believes that as a doctoral student, even if it requires a lot of time, energy, and the "high risk" of failure, it still needs to be "given a shot" to try. When I first explored the feasibility of the method, I was very careful because a good experimental method might be wasted if I didn't pay attention, "he said.

Figure 1: Morphological characteristics of a solid-state garnet lithium sulfur battery at the cathode and cathode/LLZO interface. The image is a cross-sectional scanning electron microscope image (source: ACSEnergyLetters)

During literature research, it was found that similar work had hardly been implemented before. Therefore, he started with raw material property information and made various attempts to obtain innovative inspiration. It took more than half a year for various material properties and experimental methods to be tested before discovering the feasibility of using materials in the current paper.

The biggest challenge of this study is to ensure good contact between the composite positive electrode particles, which he has been researching and exploring for a long time in this direction.

He has developed a novel three-phase sulfur positive electrode, which is composed of a mixture of sulfurized polyacrylonitrile (SPAN), molten lithium imide (LiFSI) and nanographene wire (NGW). Replacing traditional carbon black with nanographene wires has resulted in a composite positive electrode with higher mechanical strength while maintaining continuous electron conduction.

Figure 1: Schematic diagram of an all solid-state garnet Li-S battery implemented by a new three-phase cathode and a double-layer -LLZO electrolyte structure. By melting and cooling LiFSI in a SPAN+NGW+LiFSI mixture, a SPAN+NGW+LiFSI composite cathode was obtained. Grey particles, yellow particles, and black lines represent LiFSI, SPAN, and NGW, respectively (source: ACSEnergyLetters)

Surprisingly, the solid low melting point lithium salt used by the research team members has very good chemical stability with the active sulfur material. This surprised me because at the beginning of the test, I thought they would definitely have very serious side effects, but I didn't expect to find them stable after trying, "she recalled.

The melting infiltration of LiFSI into the composite cathode greatly improves the inter particle contact and cathode/electrolyte interface contact within the cathode. The all solid-state lithium sulfur battery using a heat treated three-phase cathode exhibits stable cycling performance at 60 .

Among them, it has a high average discharge capacity of 1400mAh/g at 0.167mA/cm2, exceeding 40 cycles; Under the condition of 0.84mA/cm2, it has a high average discharge capacity of 437mAh/g and over 200 cycle times. This solid-state structure is a feasible method and significant progress for achieving high energy density all solid-state lithium sulfur batteries.

Expected application in fields such as battery products and electric vehicles

In fact, this study is the third project in the research group's series of work. In their previous study, they explored the chemical and electrochemical instability between the sulfur positive electrode and LLZO interface, as well as methods to overcome this interface instability factor [2].

Based on this, in the second study, they implemented a solid-state lithium sulfur battery with ultra stable cycling, and the related paper is currently in the review stage. In the first two studies, researchers added a small amount of liquid electrolyte between the sulfur positive electrode and LLZO. It is precisely because of the accumulation of these experiences that a solid foundation has been laid for this new research.

After implementing the concept of using LLZO solid electrolyte as an all solid-state lithium sulfur battery, they then used the same method to prepare a high energy density all solid-state lithium sulfur battery using LLZO solid electrolyte.

Figure 1: Electrochemical Performance of All Solid State Double Layer LLZO Lithium Sulfur Battery at 60 (Source: ACSEnergyLetters)

I think this research is a breakthrough in the field. Previously, both the battery industry and academia believed that the possibility of achieving full solid-state oxidation of solid-state lithium sulfur batteries was very low, but we did

At present, the team is still trying to modify various materials, hoping to find better materials to achieve more stable battery cycling, higher energy density, and fast charging technology. It is reported that his doctoral supervisor, Professor Waxman, has founded a related company and may apply this technology to practical production fields in the future.

I am very optimistic about the development prospects of solid-state batteries, especially in the fields of low and ultra-high temperatures, as well as in the application of battery products and electric vehicles in daily life. I also hope that this technology can be directly put into use as soon as possible, "he said.

Committed to the practical application of solid-state batteries

He graduated with a bachelor's degree in metallurgy from Beijing University of Science and Technology. Afterwards, he went to the research group of teachers at Columbia University in the United States to conduct research on flexible lithium-ion batteries. In fact, at the time of his master's degree, solid-state batteries were still in their early stages and were still in a relatively novel field.

At that time, there were very few research groups in the United States that worked on solid-state batteries. Based on his previous research background in batteries, during his doctoral studies at the University of Maryland, he chose to continue his research in the solid-state field.

So, what is the research life of a doctoral student in the field of solid-state batteries? Although many people are complaining about 996 now, he believes that 996 is "quite easy" in the field of scientific research. In fact, the atmosphere of Professor Eric D. Vauxman's research group is relatively relaxed, and he does not push or rush students to do research that can be completed within a year or two.

This gives us a lot of room for growth, but I have quite strict requirements for myself, most of whom are still in the state of 9107. When there are no results from the research, there is a lot of pressure and it is difficult to sleep, "he said. Whenever this happens, he simply invests all his time in scientific research.

For example, in order to save experimental time, after the epidemic, he occasionally goes to school at around 3am to burn ceramic tiles, because this way he can burn them well that night. This ensures that subsequent experiments can continue on the same day without the need to wait overnight.

Compared with traditional liquid batteries, the difficulty coefficient of studying solid-state batteries is much higher, from preparing solid-state ceramic chips to battery assembly, and then to battery cycling. In fact, doctoral students or researchers in the field of solid-state batteries may have the same feelings as me. Not only does it require a lot of physical exertion, but it also requires the ability to withstand great pressure and tests both physically and mentally. However, when doing scientific research, especially research from 0 to 1, the moment you try it out is the most fulfilling and fulfilling moment, feeling that you have contributed to the entire field

With such unremitting perseverance, he has gradually gained a series of achievements, and so far, he has published four papers. During his doctoral studies, he also received awards such as the NanoResearchEnergy Youth Editorial Committee Member and Outstanding Graduate Student Award.

Currently, Professor Brian Shelton's research group at Brown University in the United States is conducting postdoctoral research. During his master's and doctoral studies, he focused on electrochemical research, and in order to broaden and open up research directions, he chose to conduct mechanical research with battery materials as the background in his postdoctoral studies. At present, he is conducting interdisciplinary research with the research group. In the future, we hope to make continuous efforts to achieve further practical applications in the field of solid-state batteries, "he said.

reference material:

1.ChangminShietal.ACSEnergyLetters2023,8,18031810 https://doi.org/10.1021/acsenergylett.3c00380

2.ChangminShietal.3DAsymmetricBilayerGarnet-HybridizedHigh-Energy-DensityLithiumSulfurBatteries.ACSAppliedMaterials& Interfaces2023,15,1,751760 https://pubs.acs.org/doi/full/10

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