The advent of a Li+ or Na+ glass electrolyte with a cation conductivity σi > 10−2 S cm−1 at 25 °C and a motional enthalpy ΔHm = 0.06 eV that is wet by a metallic lithium or sodium anode is used to develop a new strategy for an all-solid-state, rechargeable, metal-plating battery. During discharge, a cell plates the metal of an anode of high-energy Fermi level such as lithium or sodium onto a cathode current collector with a low-energy Fermi level; the voltage of the cell may be determined by a cathode redox center having an energy between the Fermi levels of the anode and that of the cathode current collector. This strategy is demonstrated with a solid electrolyte that not only is wet by the metallic anode, but also has a dielectric constant capable of creating a large electric-double-layer capacitance at the two electrode/electrolyte interfaces. The result is a safe, low-cost, lithium or sodium rechargeable battery of high energy density and long cycle life.
known around the world for his pioneering work that led to the invention of the rechargeable lithium-ion battery, have devised a new strategy for a safe, low-cost, all-solid-state rechargeable sodium or lithium battery cell that has the required energy density and cycle life for a battery that powers an all-electric road vehicle.
As reported in their paper in the RSC journal Energy & Environmental Science, the cells use a solid glass electrolyte having a Li+ or Na+ conductivity σi > 10-2 S cm-1at 25°C with a motional enthalpy ΔHm ≈ 0.06 eV, which promises to offer acceptable operation at lower temperatures. The glass also has a surface that is wet by metallic lithium or sodium, which allows reversible plating/stripping of an alkali-metal anode without dendrites, and an energy-gap window Eg > 9 eV that makes it stable on contact with both an alkali-metal anode and a high-voltage cathode without the formation of an SEI.
The glass also contains electric dipoles that endow it with a large dielectric constant. Optimal properties are only obtained after aging, which requires more than 10 days at 25°C, but only a few minutes at 100°C.
With this glass, a rechargeable battery with a metallic lithium or sodium anode and an insertion-compound as cathode may require a polymer or liquid catholyte in contact with the cathode. However, the team notes, the all-solid-state metal-plating batteries are simpler to fabricate at lower cost and offer much higher energy densities, longer cycle life, and acceptable charge/discharge rates.
To fabricate test cells for their study, the researchers took Na+ and Li+ glass electrolytes and introduced them into either a fiberglass sheet or a thin sheet of recycled paper from a slurry of the glass particle sin ethanol. They heated the membranes to outgas the ethanol and reform the solid glass electrolyte without grain boundaries, then pressed these against an anode of Li or Na foil contacting a stainless-steel cell container.
The electrolyte membrane was 0.06 mm thick. The cathode consisted of a redox center (an S8, or ferrocene Fe(C5H5) molecule or MnO2 particle) embedded in a mix of electrolyte and carbon contacting a Cu current collector.
This cathode composite was pressed against the electrolyte membrane in a coin-cell configuration. The sealed cell was then aged. None of the components were optimized before the electrochemical performance measurements.
| Schematic of an all-solid-state Li-S cell with the glass electrolyte; during discharge the metallic-lithium anode is plated on the cathode carbon-copper composite current collector. Click to enlarge. |
The ability to plate/strip reversibly an alkali-metal anode from a solid electrolyte invites a complete rethink of rechargeable-battery strategies. With the Li-glass and Na-glass electrolytes, we have demonstrated in this paper one possible new strategy in which the cathode consists of plating the anode alkali-metal on a copper-carbon cathode current collector at a voltage V > 3.0 V. Replacement of a host insertion compound as cathode by a redox center for plating an alkali-metal cathode provides a safe, low-cost, all-solid-state cell with a huge capacity giving a large energy density and a long cycle life suitable for powering an all-electric road vehicle or for storing electric power from wind or solar energy.
—Braga et al.
A team of engineers led by 94-year-old John Goodenough, professor in the Cockrell School of Engineering at The University of Texas at Austin and co-inventor of the lithium-ion battery, has developed the first all-solid-state battery cells that could lead to safer, faster-charging, longer-lasting rechargeable batteries for handheld mobile devices, electric cars and stationary energy storage.
Goodenough's latest breakthrough, completed with Cockrell School senior research fellow Maria Helena Braga, is a low-cost all-solid-state battery that is noncombustible and has a long cycle life (battery life) with a high volumetric energy density and fast rates of charge and discharge. The engineers describe their new technology in a recent paper published in the journal Energy & Environmental Science.
"Cost, safety, energy density, rates of charge and discharge and cycle life are critical for battery-driven cars to be more widely adopted. We believe our discovery solves many of the problems that are inherent in today's batteries," Goodenough said.
The researchers demonstrated that their new battery cells have at least three times as much energy density as today's lithium-ion batteries. A battery cell's energy density gives an electric vehicle its driving range, so a higher energy density means that a car can drive more miles between charges. The UT Austin battery formulation also allows for a greater number of charging and discharging cycles, which equates to longer-lasting batteries, as well as a faster rate of recharge (minutes rather than hours).
Today's lithium-ion batteries use liquid electrolytes to transport the lithium ions between the anode (the negative side of the battery) and the cathode (the positive side of the battery). If a battery cell is charged too quickly, it can cause dendrites or "metal whiskers" to form and cross through the liquid electrolytes, causing a short circuit that can lead to explosions and fires. Instead of liquid electrolytes, the researchers rely on glass electrolytes that enable the use of an alkali-metal anode without the formation of dendrites.
The use of an alkali-metal anode (lithium, sodium or potassium) -- which isn't possible with conventional batteries -- increases the energy density of a cathode and delivers a long cycle life. In experiments, the researchers' cells have demonstrated more than 1,200 cycles with low cell resistance.
Additionally, because the solid-glass electrolytes can operate, or have high conductivity, at -20 degrees Celsius, this type of battery in a car could perform well in subzero degree weather. This is the first all-solid-state battery cell that can operate under 60 degree Celsius.
Braga began developing solid-glass electrolytes with colleagues while she was at the University of Porto in Portugal. About two years ago, she began collaborating with Goodenough and researcher Andrew J. Murchison at UT Austin. Braga said that Goodenough brought an understanding of the composition and properties of the solid-glass electrolytes that resulted in a new version of the electrolytes that is now patented through the UT Austin Office of Technology Commercialization.
The engineers' glass electrolytes allow them to plate and strip alkali metals on both the cathode and the anode side without dendrites, which simplifies battery cell fabrication.
Another advantage is that the battery cells can be made from earth-friendly materials.
"The glass electrolytes allow for the substitution of low-cost sodium for lithium. Sodium is extracted from seawater that is widely available," Braga said.
Goodenough and Braga are continuing to advance their battery-related research and are working on several patents. In the short term, they hope to work with battery makers to develop and test their new materials in electric vehicles and energy storage devices.
Resources
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Maria Helena Braga, Nicholas S. Grundish, Andrew J. Murchison and John B Goodenough (2016) “Alternative Strategy for a Safe Rechargeable Battery” Energy Environ. Sci. doi: 10.1039/C6EE02888H
Source:http://pubs.rsc.org/en/Content/ArticleLanding/2017/EE/C6EE02888H#!divRelatedContent
Source:http://www.greencarcongress.com/2016/12/20161213-braga.html
Source:https://www.sciencedaily.com/releases/2017/02/170228131144.htm
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