Fluorinated Cations Enable Robust Lithium-Metal Batteries

Introduction to High-Energy Batteries

Batteries are essential for powering our modern devices, from smartphones to electric vehicles. As our reliance on technology grows, the demand for

that can store more power and last longer has become increasingly important. However, the current battery technologies come with some environmental and cost concerns.

Developing a New Approach for Robust Battery Performance

Researchers have been working on finding a solution to this problem, and they have presented a new approach that does not rely on high fractions of

in the

electrolytes

The chemical solution that allows the flow of electricity between the positive and negative electrodes in a battery.

 

. This is significant because using large amounts of fluorinated compounds can have a negative impact on the environment and increase the cost of producing high-energy batteries.

The researchers' strategy involves using very low fractions (around 0.1 percent by weight) of readily

in the electrolyte. These cations are attracted to the surface of the battery's

anode

The negative electrode in a battery where chemical reactions occur during charging and discharging.

 

, where they form a robust, fluorine-rich

solid electrolyte interphase

A thin layer that forms on the surface of the anode, which helps protect the anode and improve battery performance.

 

(

SEI

An abbreviation for 'solid electrolyte interphase', which is a protective layer that forms on the anode in a battery.

 

). This SEI layer helps prevent the growth of

dendrites

Needle-like structures that can grow on the anode of a battery, which can cause short circuits and safety issues.

 

, which are needle-like structures that can form on the anode and cause the battery to short-circuit.

Improving Oxidative Stability and Suppressing Corrosion

In addition to the SEI layer, the researchers also investigated the use of fluorinated cations, specifically TFP+, to improve the

of the electrolyte. This is important because the electrolyte needs to be able to withstand the high voltages used by modern, high-energy

cathodes

The positive electrode in a battery, where chemical reactions occur during the discharge process. The cathode material plays a crucial role in determining the energy density and performance of a battery.

 

like

NCM811

A type of high-energy cathode material for lithium-ion batteries, composed of nickel, cobalt, and manganese in an 8:1:1 ratio. This material can provide high energy density but may be less stable at high voltages.

 

.

The researchers found that the addition of TFP+ and

to the electrolyte shifted the potential for oxidative decomposition to higher voltages, allowing the use of these high-voltage cathodes. Cells with the TFP-containing electrolyte demonstrated dramatically improved cycling stability, maintaining 94% of their discharge capacity after 275 cycles, compared to cells without the additive.

The presence of TFP+ also helped suppress the corrosion of the

, which can be caused by chlorine impurities in the electrolyte. This further contributes to the long-term stability and performance of the full battery cell.

Understanding the Mechanisms Behind the Improvements

To understand how the fluorinated cations were able to improve the battery's performance, the researchers conducted a series of experiments and computational modeling.

The experiments showed that the fluorinated cations undergo reduction at a higher potential than the electrolyte solvents and anions. This means that they are the first to be reduced, forming a robust and passivating

layer. This LiF-rich SEI prevents further decomposition of the electrolyte and enables stable cycling of the lithium metal anode for over 3000 hours.

The researchers also found that the TFP+ cations react with the

formed at the cathode surface to create a protective

cathode-electrolyte interphase

The layer that forms between the positive electrode (cathode) and the liquid electrolyte in a battery. This layer can affect the performance and stability of the battery.

 

(

CEI

Short for 'cathode-electrolyte interphase'. This refers to the layer that forms between the positive electrode (cathode) and the liquid electrolyte in a battery.

 

) rich in carbon-fluorine containing species. This CEI helps to suppress the oxidative decomposition of the ether-based electrolyte and the corrosion of the aluminum current collector.

Reducing Costs and Environmental Impact

The key advantage of this approach is that it can deliver the desired chemical species to the battery's electrodes through electrostatic attraction, while using only a very small amount of additive. This is in contrast to the traditional approach of using high fractions of fluorinated compounds, which can be more expensive and have a larger environmental footprint.

By using a minimal amount of fluorinated cations, the researchers were able to achieve high

of 99.6% for

lithium plating and stripping

The process of depositing and removing lithium metal on the battery's negative electrode (anode) during charging and discharging. This can affect the battery's performance and safety.

 

, which is comparable to the best-performing electrolytes containing high concentrations of fluorinated species. This means that the battery can be charged and discharged efficiently, further improving its overall performance and lifespan.

Conclusion

In summary, the researchers have developed a new approach to enable robust battery performance that does not rely on high fractions of fluorinated species in the electrolyte. By using a small amount of readily reducible fluorinated cations, they were able to form protective SEI and CEI layers that improved the battery's cycling stability, coulombic efficiency, and resistance to corrosion.

This strategy represents a significant step forward in the development of high-energy batteries, as it can notably reduce the costs and environmental impact of implementing these technologies. The researchers' work demonstrates that high fractions of fluorinated species are not necessary to generate robust battery interphases, paving the way for more sustainable and cost-effective high-energy battery solutions.