ຂ່າວອຸດສາຫະກໍາ

ການຊອກຫາໄອອອນລິທຽມຢູ່ໃນການເຄື່ອນທີ່ຢູ່ໃນແບັດເຕີຣີສາກໄວ

2021-08-09



ແຜນຜັງຂອງຈຸລັງໄຟຟ້າຂະ ໜາດ ນ້ອຍທີ່ນັກວິທະຍາສາດສ້າງຂຶ້ນເພື່ອໄລ່ ລິທຽມ ions (ສີສົ້ມ) ທີ່ເຄື່ອນຍ້າຍຢູ່ໃນເຄືອຂອງ LTO (ສີຟ້າ). ສິນເຊື່ອ: ຫ້ອງທົດລອງແຫ່ງຊາດ Brookhaven

 

ທີມນັກວິທະຍາສາດ ນຳ ໂດຍຫ້ອງທົດລອງແຫ່ງຊາດກະຊວງພະລັງງານຂອງສະຫະລັດອາເມລິກາ (DOE) Brookhaven ແລະຫ້ອງທົດລອງແຫ່ງຊາດ Lawrence Berkeley ໄດ້ບັນທຶກເວລາຕົວຈິງວ່າໄອອອນ ລິທຽມ ເຄື່ອນທີ່ຢູ່ໃນ ລິທຽມ titanate (LTO), ວັດສະດຸໄຟຟ້າຂອງແບັດເຕີຣີທີ່ສາກໄວໄດ້ຈາກ ລິທຽມ, titanium , ແລະອົກຊີເຈນ. ເຂົາເຈົ້າຄົ້ນພົບວ່າການຈັດແຈງຂອງລິທຽມລິທຽມແລະປະລໍາມະນູອ້ອມຂ້າງທີ່ບິດເບືອນຢູ່ໃນ LTO "ຕົວກາງ" (ໂຄງສ້າງຂອງ LTO ທີ່ມີຄວາມເຂັ້ມຂຸ້ນຂອງລິທຽມຢູ່ໃນລະຫວ່າງສະຖານະການເບື້ອງຕົ້ນແລະຈຸດສິ້ນສຸດຂອງມັນ) ໃຫ້ "ທາງດ່ວນ" ສໍາລັບການຂົນສົ່ງທາດໄອອອນລິທຽມ. ການຄົ້ນພົບຂອງເຂົາເຈົ້າ, ລາຍງານຢູ່ໃນວາລະສານວິທະຍາສາດໃນວັນທີ 28 ກຸມພາ, ສາມາດໃຫ້ຄວາມເຂົ້າໃຈໃນການອອກແບບວັດສະດຸແບັດເຕີຣີທີ່ໄດ້ຮັບການປັບປຸງດີຂຶ້ນສໍາລັບການສາກໄຟໄວຂອງລົດໄຟຟ້າແລະເຄື່ອງໃຊ້ໄຟຟ້າແບບພົກພາເຊັ່ນ: ໂທລະສັບມືຖືແລະແລັບທັອບ.

 

"ພິຈາລະນາວ່າມັນໃຊ້ເວລາພຽງແຕ່ສອງສາມນາທີເພື່ອເຕີມຖັງແກັດຂອງລົດ, ແຕ່ສອງສາມຊົ່ວໂມງເພື່ອສາກແບັດເຕີຣີຂອງລົດໄຟຟ້າ," ກ່າວໂດຍທ່ານ Feng Wang, ນັກວິທະຍາສາດວັດສະດຸຢູ່ໃນພະແນກວິທະຍາສາດວິທະຍາສາດຂອງ Brookhaven Lab. "ກຳ ລັງຄິດໄລ່ວິທີເຮັດລິທຽມໄອອອນເຄື່ອນໄວຂຶ້ນຢູ່ໃນວັດສະດຸໄຟຟ້າເປັນເລື່ອງໃຫຍ່, ເພາະມັນອາດຈະຊ່ວຍໃຫ້ພວກເຮົາສ້າງແບັດເຕີຣີທີ່ດີກວ່າພ້ອມກັບຫຼຸດເວລາສາກລົງໄດ້ຫຼາຍ. "

 

Lithium-ion batteries work by shuffling ລິທຽມ ions between a positive and negative electrode (cathode and anode) through a chemical medium called an electrolyte. Graphite is commonly employed as the anode in state-of-the-art ລິທຽມ-ion batteries, but for fast-charging applications, LTO is an appealing alternative. LTO can accommodate ລິທຽມ ions rapidly, without suffering from ລິທຽມ plating (the deposition of ລິທຽມ on the electrode surface instead of internally).

 

As LTO accommodates ລິທຽມ, it transforms from its original phase (Li4Ti5O12) to an end phase (Li7Ti5O12), both of which have poor ລິທຽມ conductivity. Thus, scientists have been puzzled as to how LTO can be a fast-charging electrode. Reconciling this seeming paradox requires knowledge of how ລິທຽມ ions diffuse in intermediate structures of LTO (those with a ລິທຽມ concentration in between that of Li4Ti5O12 and Li7Ti5O12), rather than a static picture derived solely from the initial and end phases. But performing such characterization is a nontrivial task. Lithium ions are light, making them elusive to traditional electron- or X-ray-based probing techniques—especially when the ions are shuffling rapidly within active materials, such as LTO nanoparticles in an operating battery electrode.

 

In this study, the scientists were able to track the migration of ລິທຽມ 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 conduct electron energy-loss spectroscopy (EELS) during battery charge and discharge. In EELS, the change in energy of electrons after they have interacted with a sample is measured to reveal information about the sample's local chemical states. In addition to being highly sensitive to ລິທຽມ ions, EELS, when carried out inside a TEM, provides the high resolution in both space and time needed to capture ion transport in nanoparticles.

 

"The team tackled a multifold challenge in developing the electrochemically functional cell—making the cell cycle like a regular battery while ensuring it was small enough to fit into the millimeter-sized sample space of the TEM column,'' said co-author and senior scientist Yimei Zhu, who leads the Electron Microscopy and Nanostructure Group in Brookhaven's Condensed Matter Physics and Materials Science (CMPMS) Division. "To measure the EELS signals from the ລິທຽມ, a very thin sample is needed, beyond what is normally required for the transparency of probing electrons in TEMs."

 

The resulting EELS spectra contained information about the occupancy and local environment of ລິທຽມ at various states of LTO as charge and discharge progressed. To decipher the information, 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. On the basis of these simulations, they determined the arrangements of atoms from among thousands of possibilities. To determine the impact of the local structure on ion transport, the CEDER group calculated the energy barriers of ລິທຽມ-ion migration in LTO, using methods based on quantum mechanics.

 

Lithium ions quickly moving along "easy pathways" in intermediate configurations of LTO. Imagine the LTO lattice as a racecar obstacle course that the ລິທຽມ ions have to navigate around. In its original phase (Li4Ti5O12) and the end phase it transforms into to accommodate ລິທຽມ ions (Li7Ti5O12), LTO has atomic configurations in which many obstacles are in the way. Thus, ລິທຽມ ions must travel slowly through the obstacle course. But in intermediate configurations of LTO (such as the Li5+xTi5O12 shown in the movie), local distortions in the arrangement of atoms surrounding ລິທຽມ occur along the boundary of these two phases. These distortions slightly shovel the obstacles out of the way, giving rise to a "fast lane" for ລິທຽມ ions to speed through. Credit: Brookhaven National Laboratory

 

"Computational modeling was very important to understand how ລິທຽມ can move so fast through this material," said co-corresponding author and CEDER group leader Gerbrand Ceder, Chancellor's Professor in the Department of Materials Science and Engineering at UC Berkeley and a senior faculty scientist in the Materials Science Division at Berkeley Lab. "As the material takes up ລິທຽມ, the atomic arrangement becomes very complex and difficult to conceptualize with simple transport ideas. Computations were able to confirm that the crowding of ລິທຽມ ions together makes them highly mobile."

 

ທ່ານ Deyu Lu, ນັກຟີຊິກສາດໃນກຸ່ມທິດສະດີແລະການຄິດໄລ່ CFN ກ່າວວ່າ "ລັກສະນະສໍາຄັນຂອງວຽກງານນີ້ແມ່ນການປະສົມປະສານຂອງການທົດລອງແລະການຈໍາລອງ, ເພາະວ່າການຈໍາລອງສາມາດຊ່ວຍພວກເຮົາຕີຄວາມຂໍ້ມູນການທົດລອງແລະພັດທະນາຄວາມເຂົ້າໃຈທາງກົນຈັກ." "ຄວາມຊ່ຽວຊານໃນການວັດແທກສາຍຕາທີ່ພວກເຮົາໄດ້ພັດທະນາຢູ່ທີ່ CFN ຕະຫຼອດຫຼາຍປີຜ່ານມາມີບົດບາດສໍາຄັນໃນໂຄງການຜູ້ໃຊ້ຮ່ວມມືນີ້ໃນການກໍານົດລາຍນີ້ວມືທີ່ສໍາຄັນໃນ EELS ແລະແກ້ໄຂຕົ້ນກໍາເນີດທາງດ້ານຮ່າງກາຍຂອງເຂົາເຈົ້າໃນໂຄງສ້າງອາຕອມແລະຄຸນສົມບັດເອເລັກໂຕຣນິກຂອງເຂົາເຈົ້າ."

 

The team's analysis revealed that LTO has metastable intermediate configurations in which the atoms are locally not in their usual arrangement. These local "polyhedral" distortions lower the energy barriers, providing a pathway through which ລິທຽມ ions can quickly travel.

 

"Unlike gas freely flowing into your car's gas tank, which is essentially an empty container, ລິທຽມ needs to "fight" its way into LTO, which is not a completely open structure," explained Wang. "To get ລິທຽມ in, LTO transforms from one structure to another. Typically, such a two-phase transformation takes time, limiting the fast-charging capability. However, in this case, ລິທຽມ is accommodated more quickly than expected because local distortions in the atomic structure of LTO create more open space through which ລິທຽມ can easily pass. These highly conductive pathways happen at the abundant boundaries existing between the two phases."

 

Next, the scientists will explore the limitations of LTO—such as heat generation and capacity loss associated with cycling at high rates—for real applications. By examining how LTO behaves after repeatedly absorbing and releasing ລິທຽມ at varying cycling rates, they hope to find remedies for these issues. This knowledge will inform the development of practically viable electrode materials for fast-charging batteries.

 

ທ່ານ Zhu ກ່າວວ່າ "ຄວາມພະຍາຍາມຂອງສະຖາບັນຂ້າມຊາດທີ່ປະສົມປະສານກັນຢູ່ໃນສະເປັກ, ການຄິດໄລ່ໄຟຟ້າ, ການ ຄຳ ນວນ, ແລະທິດສະດີໃນວຽກງານນີ້ໄດ້ວາງຕົວແບບໃນການຄົ້ນຄ້ວາໃນອະນາຄົດ."

 

"We look forward to examining transport behaviors in fast-charging electrodes more closely by fitting our newly developed electrochemical cell to the powerful electron and X-ray microscopes at Brookhaven's CFN and National Synchrotron Light Source II (NSLS-II)," said Wang. "By leveraging these state-of-the-art tools, we will be able to gain a complete view of ລິທຽມ transport in the local and bulk structures of the samples during cycling in real time and under real-world reaction conditions."