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Using biology to improve lithium ion batteries
Materials Today Volume 18, Number 4 May 2015
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Wang’s team has focused on 2D semiconductors with the MX2 format. A transition metal monolayer of, for instance, molybdenum (Mo) or tungsten (W), sandwiched between two layers of a chalcogen, such as sulfur (S) or selenium (Se). These atomically thin 2D materials have the same hexagonal honeycombed lattice as graphite, or indeed graphene. Unlike graphene, MX2 materials have a natural band gap that would make them useful in transistors and other electronic devices. The team has previously reported experimental observations with photo-excited MX2 materials displaying an ultrafast charge transfer of less than 50 fs. This transfer rate is on a par with that observed in graphene. Wang explains their current re-
valley-selective optical Stark effect in WSe2 monolayers from the non-resonant pump that resulted in an energy splitting of more than 10 meV between the K and K0 valley exciton transitions. As controlling valley excitons with a real magnetic field is difficult to achieve even with superconducting magnets, a light-induced pseudo-magnetic field is highly desirable.’ Valleytronics could offer advantages in data processing speeds over conventional electronics. It also precludes the kind of interference from magnetic fields that could be a problem for spintronics. ‘Coherent manipulation of valley polarization should open up fascinating opportunities for valleytronics,’ Wang adds. David Bradley
Credit: Image courtesy of Feng Wang, Berkeley Lab.
search: ‘Using ultrafast pump-probe spectroscopy, we were able to observe a pure and
Using biology to improve lithium ion batteries A new study has taken a lesson from biology to show how the performance of lithium ion (Li-ion) batteries can be improved. A team from the University of Maryland, Baltimore County, borrowed a technique that organisms use to build the mineralized tissues that comprise bones, teeth and shell to show how biological molecules can latch onto nanoscale components, locking them into position to help produce high-performing Li-ion battery electrodes. The development of mineralized tissues is helped by specialized peptides, organic molecules made by the cells of living things. These peptides can bind to the particular inorganic molecules required to create that tissue and hold them in place, but can also help create very fine structures with fabricated materials. In this study, presented at the 59th annual meeting of the Biophysical Society held recently in Baltimore, a bi-functional peptide that binds strongly to lithium manganese nickel oxide (LMNO) – used in the manufacture of cathodes in highperformance batteries – was isolated. The peptide locked onto nanosized particles of LMNO, connecting them to conductive components of a battery electrode, improving both its potential power and stability. Using the ‘phage display’ approach, more than a billion potential peptides were screened to find one that would adhere strongly enough to LMNO. The new peptide was then combined with a previously
Images on the left show no specific interactions between cathode material LiNi0.5Mn1.5O4 and MWCNTs, observe formation of CNTs bundles that attached to material non-specifically during water evaporation from the TEM grid. Images on the right indicate that presence of multifunctional 24-mer peptide with two binding domains, one for LMNO and another for CNTs, allows to form dispersed CNTs conjugated to LMNO particles at the nanoscale.
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isolated peptide that binds to carbon nanotubes, which can act as conductive nanowires. When these two specialized peptides are combined, they can form a ‘nanobridge’ between the two components of the cathode, keeping them near one another to maintain a connection through multiple charging cycles. As researcher Evgenia Barannikova said, this helps to ‘prevent disaggregation of electroactive and conductive material, which currently
184
Materials Today Volume 18, Number 4 May 2015
results in loss of conductivity and low performance of some batteries’. Nanostructured electrodes in Li-ion batteries offer advantages over bulk material electrodes, such as shorter distances for chargecarrying particles to travel and a high surface area, providing more active sites for electrochemical reactions to occur, potentially leading to lighter and longer-lasting batteries. Studies into the surface interactions between solid-binding peptides and inor-
ganic materials are also important for applications such as biomedicine, electronics, data storage, sensors, optics and catalysis. The team is now testing the efficiency of the new cathodes, and aim to produce an anode using similar techniques and integrate the two components, offering new ways of developing devices based on the assembly of materials at the nanoscale. Laurie Donaldson
NEWS
Wang’s team has focused on 2D semiconductors with the MX2 format. A transition metal monolayer of, for instance, molybdenum (Mo) or tungsten (W), sandwiched between two layers of a chalcogen, such as sulfur (S) or selenium (Se). These atomically thin 2D materials have the same hexagonal honeycombed lattice as graphite, or indeed graphene. Unlike graphene, MX2 materials have a natural band gap that would make them useful in transistors and other electronic devices. The team has previously reported experimental observations with photo-excited MX2 materials displaying an ultrafast charge transfer of less than 50 fs. This transfer rate is on a par with that observed in graphene. Wang explains their current re-
valley-selective optical Stark effect in WSe2 monolayers from the non-resonant pump that resulted in an energy splitting of more than 10 meV between the K and K0 valley exciton transitions. As controlling valley excitons with a real magnetic field is difficult to achieve even with superconducting magnets, a light-induced pseudo-magnetic field is highly desirable.’ Valleytronics could offer advantages in data processing speeds over conventional electronics. It also precludes the kind of interference from magnetic fields that could be a problem for spintronics. ‘Coherent manipulation of valley polarization should open up fascinating opportunities for valleytronics,’ Wang adds. David Bradley
Credit: Image courtesy of Feng Wang, Berkeley Lab.
search: ‘Using ultrafast pump-probe spectroscopy, we were able to observe a pure and
Using biology to improve lithium ion batteries A new study has taken a lesson from biology to show how the performance of lithium ion (Li-ion) batteries can be improved. A team from the University of Maryland, Baltimore County, borrowed a technique that organisms use to build the mineralized tissues that comprise bones, teeth and shell to show how biological molecules can latch onto nanoscale components, locking them into position to help produce high-performing Li-ion battery electrodes. The development of mineralized tissues is helped by specialized peptides, organic molecules made by the cells of living things. These peptides can bind to the particular inorganic molecules required to create that tissue and hold them in place, but can also help create very fine structures with fabricated materials. In this study, presented at the 59th annual meeting of the Biophysical Society held recently in Baltimore, a bi-functional peptide that binds strongly to lithium manganese nickel oxide (LMNO) – used in the manufacture of cathodes in highperformance batteries – was isolated. The peptide locked onto nanosized particles of LMNO, connecting them to conductive components of a battery electrode, improving both its potential power and stability. Using the ‘phage display’ approach, more than a billion potential peptides were screened to find one that would adhere strongly enough to LMNO. The new peptide was then combined with a previously
Images on the left show no specific interactions between cathode material LiNi0.5Mn1.5O4 and MWCNTs, observe formation of CNTs bundles that attached to material non-specifically during water evaporation from the TEM grid. Images on the right indicate that presence of multifunctional 24-mer peptide with two binding domains, one for LMNO and another for CNTs, allows to form dispersed CNTs conjugated to LMNO particles at the nanoscale.
183
NEWS
isolated peptide that binds to carbon nanotubes, which can act as conductive nanowires. When these two specialized peptides are combined, they can form a ‘nanobridge’ between the two components of the cathode, keeping them near one another to maintain a connection through multiple charging cycles. As researcher Evgenia Barannikova said, this helps to ‘prevent disaggregation of electroactive and conductive material, which currently
184
Materials Today Volume 18, Number 4 May 2015
results in loss of conductivity and low performance of some batteries’. Nanostructured electrodes in Li-ion batteries offer advantages over bulk material electrodes, such as shorter distances for chargecarrying particles to travel and a high surface area, providing more active sites for electrochemical reactions to occur, potentially leading to lighter and longer-lasting batteries. Studies into the surface interactions between solid-binding peptides and inor-
ganic materials are also important for applications such as biomedicine, electronics, data storage, sensors, optics and catalysis. The team is now testing the efficiency of the new cathodes, and aim to produce an anode using similar techniques and integrate the two components, offering new ways of developing devices based on the assembly of materials at the nanoscale. Laurie Donaldson