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[Due to the increasing size of the archives, each topic page now contains only the prior 365 days of content. Access to older stories is now solely through the Monthly Archive pages or the site search function.]

Yale team develops dendrimer-graphene oxide composite film for improved cycling of Li-sulfur batteries

March 23, 2017

Researchers at Yale University developed an ultrathin functionalized dendrimer–graphene oxide composite film that can be applied to virtually any sulfur cathode in a Li-sulfur (Li-S) battery system to alleviate capacity fading over battery cycling without compromising the energy or power density of the entire battery.

Sulfur electrodes coated with the composite film exhibit very good cycling stability, together with high sulfur content, large areal capacity, and improved power rate. The film design provides a new strategy for confining lithium polysulfides. A paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).

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PNNL team finds electrolyte additive enables fast charging, stable cycling Li-metal batteries

March 01, 2017

Researchers at Pacific Northwest National Laboratory (PNNL) have found that adding a small, optimal amount (0.05M) of LiPF6 (lithium hexafluorophosphate) as an additive in LiTFSI–LiBOB dual-salt/carbonate-solvent-based electrolytes significantly enhances the charging capability and cycling stability of Li metal batteries. A paper on their work is published in the journal Nature Energy.

In the paper, they report that using the additive in a Li metal battery with a 4-V Li-ion cathode at a moderately high loading of 1.75 mAh cm−2 resulted in 97.1% capacity retention after 500 cycles along with very limited increase in electrode overpotential at a charge/discharge current density up to 1.75 mA cm−2. The researchers attributed the fast charging and stable cycling performances to the generation of a robust and conductive solid electrolyte interphase at the Li metal surface and stabilization of the Al cathode current collector.

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Goodenough and UT team report new strategy for all-solid-state Na or Li battery suitable for EVs; plating cathodes

A team of engineers led by 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 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. An open-access paper on the work is published in the RSC journal Energy & Environmental Science.

The cells use a solid glass electrolyte having a Li+ or Na+ conductivity >10-2 S cm-1 at 25 ˚C with a motional enthalpy ≈ 0.06 eV, which promises to offer acceptable operation at lower temperatures. Using the new glass, the cathode consists of plating the anode alkali-metal (e.g., (lithium, sodium or potassium) on a copper–carbon cathode current collector at a voltage of more than 3.0 V. Replacing a conventional host insertion compound as a cathode by a redox center for plating an alkali-metal cathode provides a safe, low-cost, all-solid-state cell with a large capacity resulting in high energy density and a long cycle life.

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USC team uses mixed conduction membranes to suppress polysulfide shuttle in Li-S batteries

February 17, 2017

One of the major issues hobbling the commercialization of high energy-density lithium-sulfur batteries is the “polysulfide shuttle”—the shuttling of polysulfide ions between the cathode and anode. The polysulfide shuttle is a major technical issue that limits the electrical performance and cycle life of this type of battery. Addressing this polysulfide shuttle—which causes self-discharge, low charging efficiencies, and irreversible capacity losses—has been a major focus of research and development.

Now, in an open-access paper published in the January issue of the Journal of the Electrochemical Society, Sri Narayan and Derek Moy of the USC Loker Hydrocarbon Research Institute report a novel approach to the problem. The USC team developed a “mixed conduction membrane” (MCM)—a thin non-porous lithium-ion conducting barrier that simply restricts the soluble polysulfides to the positive electrode.

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Researchers suggest approach for boosting Li-S performance; conversion of Li2S to sulfur without polysulfides

February 06, 2017

Lithium-sulfur batteries are one of the most promising alternatives for next-generation high-energy-density batteries; however, one of the main obstacles to widespread commercialization that still needs to be addressed is the polysulfide shuttle mechanism between the two electrodes. The polysulfide shuttle—the migration of lithium polysulfides formed during charge and discharge from cathode to anode—leads to serious self-discharge, poor efficiency and limited cycle life. (E.g., earlier post.)

Now, an international team of researchers in Europe is suggesting a possible approach to convert Li2S into sulfur without the detectible formation of polysulfides. A paper on their work is published in the Journal of Power Sources.

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Researchers develop robust biopolymer network binder enabling high sulfur loading in Li-S electrodes

December 24, 2016

Researchers from China and Australia have developed a mechanically robust biopolymer network binder that enabled the preparation of high-loading sulfur electrodes to improve the electrochemical performance of Li-sulfur batteries. The binder supported a high-sulfur-loading electrode of 19.8 mg cm-2 with an ultrahigh areal specific capacity of 26.4 mAh cm-2.

The network binder effectively prevented polysulfides within the electrode from shuttling and, consequently, improved electrochemical performance. This study, published in the RSC journal Energy & Environmental Science, identifies a new way to obtaining high-energy-density batteries by the simple application of robust network biopolymer binders that are inherently low-cost and environmentally friendly.

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Caltech, CMU researchers measure mechanical properties of Li at small scale; implications for Li metal anode development

December 21, 2016

Likely next-generation battery chemistries such as Li-sulfur or Li-air envision the use of a Li metal anode coupled with an advanced cathode. However, the use of lithium metal anodes in rechargeable batteries has been restricted due to dendrite growth that can cause short-circuits or explosions. Solid-state electrolytes appear to be a promising solution to suppress dendrite growth. However, a lack of knowledge of the mechanical properties of lithium at the very small scale (nano- and micro-) hampers the understanding of the mechanical interactions at the interface of the electrolyte with the Li electrode.

Now, a joint team of researchers from Caltech and Carnegie Mellon University has measured for the first time the strength of lithium metal at the nano- and micro-scale. In a paper in Proceedings of the National Academy of Sciences (PNAS), they report that that Li exhibits a strong size effect at room and elevated temperature. First-principle calculations show a high level of elastic anisotropy (variation of elastic properties with direction of measurement). Based on the results, they suggest rational guidelines for anode/electrolyte selection and operating conditions that will lead to better cycling performance.

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UT Austin team uses polypyrrole-MnO2 coaxial nanotubes as sulfur host to improve performance of Li−sulfur battery

December 05, 2016

Researchers at the University of Texas at Austin have developed a novel electrode for lithium-sulfur batteries that improves cyclic stability and rate capability significantly. In a paper published in the ACS journal Nano Letters, they report using polypyrrole-MnO2 coaxial nanotubes to encapsulate sulfur. MnO2 restrains the shuttle effect of polysulfides greatly through chemisorption and the polypyrrole serves as conductive frameworks.

They report a stable Coulombic efficiency of ∼98.6% and a decay rate of 0.07% per cycle with 500 cycles at 1C-rate with the S/PPy-MnO2 ternary electrodes with 70 wt % sulfur and 5 wt % of MnO2. The ternary electrodes have an initial high rate of 1420 milliampere-hours per gram (mAh/g) at 0.2 C and deliver 985 mAh/g after 200 cycles.

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U-M team uses new technique to provide in-depth understanding of dendrite growth on Li metal anodes

October 19, 2016

A team at the University of Michigan (U-M) has used operando video microscopy to develop a comprehensive understanding of the voltage variations observed during Li metal cycling, which is directly correlated to dendrite growth. Specifically, they observed the evolution of the morphology of the Li electrode through operando high-resolution video capture, and directly correlated the morphology to time synchronized voltage traces.

They then developed a model to relate electrode morphology and competing electrochemical kinetics to cell voltage. This allowed for an in-depth understanding of the electrochemical processes occurring. This work, published in an open-access paper in ACS Central Science, provides a level of detailed understanding that can help researchers take the next steps toward bringing Li metal anodes to commercial reality.

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Sulfur-loaded carbon aerogel as cathode for Li-S battery offers improved cyclic stability

October 10, 2016

Researchers at South China Normal University in Guangzhou have developed a novel composite of sulfur loaded in micropore-rich carbon aerogel (CA-S) for use as a cathode in Li-sulfur batteries.

Compared to sulfur loaded in a common carbon material, acetylene black (AB-S), the CA-S exhibited significantly improved cyclic stability and rate capability. The CA is micropore-rich with micropore volume over 66% of total pore volume. In a paper in the Journal of Power Sources, and team attributed the improved performance of CA-S to the confinement of the micropores in CA to small sulfur allotropes and corresponding lithium sulfides.

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New high-performance foldable cathode for Li-S batteries based on 3D activated carbon fiber matrix

September 28, 2016

A team at Sun Yat-sen University in China has developed new high-performance, stable cathode for Li-S batteries consisting of a 3D activated carbon fiber matrix (ACFC) and sulfur.

The structured 3D foldable sulfur cathode (ACFC-S) delivers a reversible capacity of about 979 mAh g−1 at 0.2C; a capacity retention of 98% after 100 cycles; and 0.02% capacity attenuation per cycle. Even at an areal capacity of 6 mAh cm−2—2 times higher than the values of Li-ion batteries—it still maintains an excellent rate capability and cycling performance. An open access paper on their work is published in Scientific Reports.

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MIT team discovers two mechanisms at work in Li dendrite formation

September 02, 2016

Researchers at MIT have carried out the most detailed analysis yet of lithium dendrite formation from lithium anodes in batteries and have found that there are two entirely different mechanisms at work. While both forms of deposits are composed of lithium filaments, the way they grow depends on the applied current.

Clustered, “mossy” deposits, which form at low rates, turn out to grow from their roots and can be relatively easy to control. More sparse and rapidly advancing “dendritic” projections grow only at their tips. The dendritic type, the researchers say, are harder to deal with and are responsible for most of the problems dendrites cause: degraded performance and short-circuits that damage or disable the battery. Their findings are reported in an open-access paper in the RSC journal Energy and Environmental Science.

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DOE HPC4Mfg program funds 13 projects to advance US manufacturing; welding, Li-S batteries among projects

August 31, 2016

A US Department of Energy (DOE) program designed to spur the use of high performance supercomputers to advance US manufacturing has funded 13 new industry projects for a total of $3.8 million. Among the projects selected are one by GM and EPRI of California to improve welding techniques for automobile manufacturing and power plant builds in partnership with Oak Ridge National Laboratory (ORNL).

Another one of the 13 projects is led by Sepion Technologies, which will partner with LBNL to make new membranes to increase the lifetime of Li-S batteries for hybrid airplanes.

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Berkeley Lab researchers devise ant-nest-like structure for promising Li-S electrodes

August 11, 2016

Inspired by the structure of ant nests, researchers at Lawrence Berkeley National Laboratory have devised a novel Li–S electrode featuring increased sulfur loading and sulfur/inactive-materials ratio to improve life and capacity.

In a paper in the ACS journal Nano Letters, the team reports that the efficient capabilities of the ant-nest structure facilitate fast ion transportation, sustain polysulfide dissolution, and assist efficient precipitation. High cycling stability in the Li–S batteries, for practical applications, has been achieved with up to 3 mg·cm–2 sulfur loading. They also achieved Li–S electrodes with up to a 85% sulfur ratio.

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UMD team develops new nanocomposite sulfur electrode for high-performance all-solid-state Li-S batteries

June 24, 2016

A team at the University of Maryland have synthesized a mixed conducting nanocomposite sulfur electrode that consists of different nanoparticles with distinct properties of lithium storage capability, mechanical reinforcement, and ionic and electronic conductivities.

As described in a paper published in the ACS journal Nano Letters, the new nanocomposite serves as a mechanically robust and mixed conductive (ionic and electronic conductive) sulfur electrode for all-solid-state lithium–sulfur batteries (ASSLSBs). The team achieved a reversible capacity of 830 mAh/g (71% utilization of Li2S) at 50 mA/g for 60 cycles with a high rate performance at room temperature even at a high loading of Li2S (∼3.6 mg/cm2).

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Daimler investing >€7B in next 2 years in green tech; fuel cell plug-in, BEV architecture; 48V

June 13, 2016

At its TecDay event in Stuttgart, Daimler said it will invest more than €7 billion (US$7.9 billion) in green technologies in the next two years alone. Shortly, smart will be the only automaker worldwide to offer its entire model range both powered by internal combustion engines or operating on battery power. Mercedes-Benz will put the first fuel-cell-powered vehicle with plug-in technology into series production: the GLC F-CELL. In addition, the company is developing a dedicated vehicle architecture for battery-electric motor cars.

Following the company’s recent introduction of the new OM 654 diesel family (earlier post), Daimler will introduce a new family of gasoline engines in 2017, which will again set efficiency standards and will be the first ever to be equipped with a particulate filter (earlier post). The 48-volt on-board power supply will be introduced at the same time and starter-generators will become part of the standard specification. The 48V system will make fuel savings possible that previously were the exclusive domain of the high-voltage hybrid technology.

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Hunan team develops new strategy to prolong cycle life of Li-S batteries

Researchers at Hunan University, China, have developed a new strategy to suppress the diffusion of polysulfides into the electrolyte in Li-Sulfur batteries, resulting in improved performance.

As described in a paper in the Journal of Power Sources, the research tea used hydrophilic carbon paper anchored by hierarchically porous cobalt disulfides as an interlayer for capturing polysulfides through physical absorption and chemical bonding. The sulfur-graphene composite with a sulfur content of 70.5% delivers a high initial capacity of 1239.5 mAh g−1 at 0.2 C and retains a reversible capacity of 818 mAh g−1 after 200 cycles.

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OXIS Energy and Lithium Balance partner on Li-sulfur battery system for China e-scooter market; targeting spring 2018

June 08, 2016

Li-sulfur battery developer OXIS Energy UK (earlier post) and Lithium Balance of Denmark are partnering to build a prototype Lithium-sulfur battery system primarily for the e-scooter market in China. Lithium Balance is a battery management expert which has supplied its BMS systems for Li-ion based e-scooters for a decade. The E-scooter itself will be manufactured in China.

The current prototype battery has a capacity of 1.2 kWh using 10Ah OXIS Long Life cells; weighs 60% less than the current lead acid battery; and delivers a significant increase in range. The next stage is to build a second prototype using an improved Long Life chemistry (up to 20Ah) which will increase battery capacity at a reduced weight.

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Researchers develop safe and durable high-temperature Li-S battery with conventional C-S electrode using MLD alucone coating

May 25, 2016

Researchers from University of Western Ontario, Lawrence Berkeley National Laboratory (LBNL), and Canadian Light Sources (CLS) have developed a safe and durable high-temperature Li-sulfur battery using universal conventional carbon–sulfur (C-S) electrodes with a molecular layer deposited (MLD) alucone (aluminum oxide polymeric film) coating.

The MLD alucone-coated C−S electrodes demonstrate stabilized ultralong cycle life at high temperature (55 ˚C) with a capacity of more than 570 mA h g−1 after 300 cycles. The utilization of MLD enables the usage of conventional C-S cathode materials with carbonate-based electrolytes—a facile and versatile approach that can be applied to a variety of C−S electrodes without redesigning the carbon host materials. A paper on their work is published in the ACS journal Nano Letters.

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High-performance Li-S cathodes using 3D hierarchical porous nitrogen-doped aligned carbon nanotubes

May 16, 2016

Researchers from Hunan University and Changsha University in China have designed 3D hierarchical porous nitrogen-doped aligned carbon nanotubes (HPNACNTs) with well-directed 1D conductive electron paths as scaffold to load sulfur for use as a high-performance cathode in Li-S batteries. A paper on their work is published in the Journal of Power Sources.

The HPNACNTs have abundant micropores, mesopores and macropores with a relatively high specific surface area and a large total pore volume. The sulfur-HPNACNTs (with 68.8 wt% sulfur) composite exhibits a high initial discharge capacity of 1340 mAh g−1 at 0.1 C and retains as high as 979 mAh g−1 at 0.2 C after 200 cycles. It also shows high reversible capacity at high rates (817 mAh g−1 at 5 C).

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New silicon-sulfur battery built on 3D graphene shows excellent performance

April 28, 2016

Researchers at Beihang University in Beijing have developed a new Li-sulfur battery using honeycomb-like sulfur copolymer uniformly distributed onto 3D graphene (3D cpS-G) networks for a cathode material and a 3D lithiated Si-G network as anode.

In a paper published in the RSC journal Energy & Environmental Science, they reported that the full cell exhibits superior electrochemical performances in term of a high reversible capacity of 620 mAh g-1, ultrahigh energy density of 1147 Wh kg−1 (based on the total mass of cathode and anode), good high-rate capability and excellent cycle performance over 500 cycles (0.028% capacity loss per cycle).

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PNNL study identifies one of the mechanisms behind Li-sulfur battery capacity fade; the importance of electrolyte anion selection

March 31, 2016

Researchers at Pacific Northwest National Laboratory (PNNL) investigating the stability of the anode/electrolyte interface in Li-Sulfur batteries have found that Li-S batteries using LiTFSI-based electrolytes are more stable than those using LiFSI-based electrolytes.

In their study, published in the journal Advanced Functional Materials, they determined that the decreased stability is because the N–S bond in the FSI anion is fairly weak; the scission of this bond leads to the formation of lithium sulfate (LiSOx) in the presence of polysulfide species. By contrast, in the LiTFSI-based electrolyte, the lithium metal anode tends to react with polysulfide to form lithium sulfide (LiSx), which is more reversible than LiSOx formed in the LiFSI-based electrolyte.

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Stanford team develops new simple approach for viable Li-metal anodes for advanced batteries

March 25, 2016

Lithium-metal anodes are favored for use in next-generation rechargeable Li-air or Li-sulfur batteries due to a tenfold higher theoretical specific capacity than graphite (3,860 mAh/g vs. 372 mAh/g); light weight and lowest anode potential. However, safety issues resulting from dendrite formation and instability caused by volume expansion have hampered development and deployment of commercially viable solutions.

A team at Stanford led by Prof. Yi Cui has now introduced a simple approach to address both issues by effectively encapsulating lithium inside a porous host scaffold using a facile melt-infusion approach. Uniformly confined within the matrix, the lithium creates a material that can deliver a high capacity of around 2,000 mAh/g (gravimetric) or 1,900 mAh/cm3 (volumetric) as stable anodes for Li-metal batteries. A paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).

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