{"id":8451,"date":"2013-11-21T09:53:01","date_gmt":"2013-11-21T16:53:01","guid":{"rendered":"http:\/\/cafe.foundation\/blog\/?p=8451"},"modified":"2013-11-21T09:53:01","modified_gmt":"2013-11-21T16:53:01","slug":"lithium-sulfur-achieves-new-highs","status":"publish","type":"post","link":"http:\/\/cafe.foundation\/blog\/lithium-sulfur-achieves-new-highs\/","title":{"rendered":"Lithium-Sulfur Achieves New Highs"},"content":{"rendered":"

Allen Chen at the University of California at Berkeley reports that researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) \u201chave demonstrated in the laboratory a lithium-sulfur (Li\/S) battery that has\u00a0more than twice the specific energy of lithium-ion batteries<\/a>, and that lasts for more than 1,500 cycles of charge-discharge with minimal decay of the battery’s capacity,\u201d the longest cycle life reported so far for any lithium-sulfur battery.<\/p>\n

Working on the premise that if electric vehicles are to have a 300-mile range, researchers explain that batteries will need to provide a cell-level specific energy of 350 to 400 Watt-hours per kilogram (Wh\/kg), roughly double that of lithium-ion batteries.<\/p>\n

They should also manage at least 1,000, and preferably 1,500 charge-discharge cycles before showing noticeable power loss.<\/p>\n

Elton Cairns, of the Environmental Energy Technologies Division (EETD), is a professor at Berkeley in the The Berkeley Energy Storage and Conversion for Transportation and Renewables (BESTAR)<\/a> Program.\u00a0 Part of their purpose is to \u201covercome the technological barriers to next-generation batteries and fuel cells for the low emissions transportation\u00a0and grid storage technologies required for a clean, sustainable energy system.\u201d\u00a0 Cairns pushes toward a \u201cholistic\u201d approach, working on not just isolated components, but an integrated whole.\u00a0 This is part of their larger goal. “Our cells may provide a substantial opportunity for the development of zero-emission vehicles with a driving range similar to that of gasoline vehicles.”<\/p>\n

\"Berkeley's<\/a>

Berkeley’s “holistic” approach takes multiple factors into account to make their lithium-sulfur battery perform well<\/p><\/div>\n

Lithium-sulfur cells are attractive because they have \u201ca much higher theoretical specific energy than lithium-ion batteries do,” according to Cairns.\u00a0 He notes that “Lithium-sulfur batteries would also be desirable because sulfur is nontoxic, safe and inexpensive.\u201d A lower potential for thermal runaway reactions would count toward the greater safety of lithium-sulfur batteries, highly desirable in light of recent popular press over-reactions to such events.<\/p>\n

Lithium-sulfur, like lithium-ion, has significant problems to solve.\u00a0 On discharge, lithium polysulfides, dissolved from the cathode into the electrolytes, then react with the lithium anode and form a layer of Li2S around it, reducing its reactivity and shortening battery life.<\/p>\n

Like lithium-ion cells, the sulfur electrode swells and contracts up to 76 percent during charging and discharging, eventually degrading the electrode and causing sulfur particles to depart from it.<\/p>\n

The research team developed a cathode of sulfur-graphene oxide (S-GO), which can deal with changing volume of the electrode\u2019s active material when sulfur is converted to Li2S on discharge, and back to elemental sulfur on recharge.<\/p>\n

Somewhat similar to Dr. Cui\u2019s work with silicon electrodes at Stanford, the team used an elastomeric binder combining elastomeric styrene butadiene rubber (SBR) binder with a thickening agent to help hold things together overall, seeing an increase in cycle life and power density for the cell.<\/p>\n

They used cetyltrimethyl ammonium bromide (CTAB), a surfactant used in drug delivery and other chemical process to coat the sulfur electrode, preventing destructive penetration and dissolution of the electrode material by the electrolyte.<\/p>\n

They also developed \u201ca novel ionic liquid based electrolyte,\u201d which \u00a0\u201cinhibits polysulfides dissolution and helps the battery operate at a high rate, increasing the speed at which the battery can be charged up, and the power it can deliver during discharge.\u201d\u00a0 Because it is non-volatile and non-flammable, the ionic liquid-based electrolyte also significantly improves the safety of the Li-S battery.<\/p>\n

Cairns seems happy with the results so far, saying, \u201cIt’s the unique combination of these elements in the cell chemistry and design that has led to a lithium-sulfur cell whose performance has never been achieved in the laboratory before\u2014long life, high rate capability, and high cell-level specific energy,”<\/p>\n

\"Demonstrated<\/a>

Demonstrated performance in Berkeley laboratories<\/p><\/div>\n

Potential investors are invited to help the team with its next goals, \u201cincluding higher sulfur utilization, operation under extreme conditions, and scale-up. Partnerships with industry are being sought.\u201d\u00a0 The team wants to increase cell energy density, performance under extreme conditions, and build larger cells.<\/p>\n

Their paper, “A long-life, high-rate lithium\/sulfur cell: a multifaceted approach to enhancing cell performance,” appears in\u00a0Nano Letters<\/em>, authored by Min-Kyu Song (Molecular Foundry, Berkeley Lab), Yuegang Zhang (Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences) and Cairns (Environmental Energy Technologies Division, Berkeley Lab).<\/p>\n

This research was funded by the U.S. Department of Energy’s Office of Science and a University of California’s Proof of Concept Award.<\/p>\n