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New Battery Structure to Improve Battery Performance

Source: Mateusz Odziomek et al., CC BY 4.0

Batteries made from a nickel-metal-hydride or using lithium-ions as conductive membranes appeared in the early 1990s, fighting nose-to-nose to gain customer's acceptance. Today, lithium-ion batteries are the most widely used and most promising industry. Local distortions which occur in the atomic structure of the electrode during operation are responsible for the rapid storage and release of lithium ion - a discovery that has helped in the design of battery materials to reduce charging times for electric vehicles, cell phones, and other battery-powered devices.

Now (2020), a team of scientists at the Brookhaven National Laboratory and Lawrence Berkeley National Laboratory has analysed how lithium ions move in lithium titanate (LTO), a fast-charging battery electrode material made of lithium, titanium, and oxygen. They found out that distorted arrangements of lithium and surrounding atoms in LTO intermediates were a very good medium for the transport of lithium ions.

In this study, the scientists managed to research the migration of lithium ions in LTO nanoparticles in real time by designing an electrochemical cell to operate inside a transmission electron microscope (TEM). This electrochemical cell enabled the team to perform electron energy-loss spectroscopy (EELS) during battery charge and discharge. During EELS, the change in energy of electrons after having interacted with a sample was measured to obtain information about the sample’s local chemical states. In addition to being highly sensitive to lithium ions, EELS, when carried out inside a TEM, provided the high resolution in both space and time needed to capture ion transport in nanoparticles.

The resulting EELS spectra depicted the occupancy and local environment of lithium at various states of LTO as charge and discharge progressed. Then, scientists from the Computational and Experimental Design of Emerging Materials Research (CEDER) group at Berkeley and the Center for Functional Nanomaterials (CFN) at Brookhaven simulated the spectra to analyse the information. The simulations helped them analyse the arrangements of atoms from a myriad of possibilities. To determine the impact of the local structure on ion transport, the CEDER group calculated the energy barriers of lithium-ion migration in LTO, using methods based on quantum mechanics.

Scientists have long sought to improve battery performance and sustainability. In 2018, scientists presented a controllable cell structure to enable lithium plating-free (LPF) fast charging. This LPF cell gave rise to a unified charging practice independent of ambient temperature, offering a platform for the development of battery materials without temperature restrictions. They demonstrated a 9.5 Ah 170 Wh/kg LPF cell that could be charged to 80% state of charge in 15 min even at −50 °C (beyond cell operation limit). Further, the LPF cell sustained 4,500 cycles of 3.5-C charging in 0 °C with <20% capacity loss, which was a  90-times boost of life compared with a baseline conventional cell, and equivalent to >12 y and >280,000 miles of EV lifetime under this extreme usage condition, i.e., 3.5-C or 15-min fast charging at freezing temperatures.

In 2019, scientists at IBM used three different proprietary materials and discovered a chemistry for a new battery which did not use heavy metals or other substances with sourcing concerns. The materials for this battery could be extracted from seawater and laid the foundation for less invasive sourcing techniques than current material mining methods. The battery also showed great performance potential. In initial tests, it proved it could be optimized to surpass the capabilities of lithium-ion batteries in a number of individual categories including lower costs, faster charging time, higher power and energy density, strong energy efficiency and low flammability.

The main advantage of the new improved battery material is that it can help build better batteries with greatly reduced charging time. Thus, it may someday be possible to charge devices within a few minutes. The study also showed that LTO had metastable intermediate configurations in which the atoms are not in their usual arrangement. These local “polyhedral” distortions lower the energy barriers, providing a pathway through which lithium ions can quickly travel.

Next, the scientists plan to research the limitations of LT, such as capacity loss due to cycling at high rates, for real applications. They hope that examining how LTO behaves after repeatedly absorbing and releasing lithium at varying cycling rates will help find remedies for these issues. This knowledge will hopefully further the development of practically viable electrode materials for fast-charging batteries.