Elastomeric SBR used in new 480-km EV battery

ERJ staff report (TP)

California − A research team from the Lawrence Berkeley National Laboratory has a 300-mile (482-km) electric vehicle battery range in its sights, thanks to a unique combination of different electrochemical technologies including a new material called sulphur-graphene oxide (S-GO); and an enhanced binder (elastomeric styrene butadiene rubber combined with a thickener) that increases power density, reported Tina Casey for Clean Technica.

S-GO was developed in-house by Berkeley Lab, for use in next-generation EV batteries based on lithium-sulphur technology.

Sulphur has some key advantages over conventional lithium-ion battery technology in terms of storage capacity (far better), toxicity (none), cost (far less), and weight (ditto), but it is also very brittle.

The gist of the problem is that sulphur tends to be soluble in the organic solvents used in conventional batteries. That process forms polysulfide ions which can get to the lithium anode and re-solidify as precipitates, forming a barrier that interferes with storage capacity.

The result is that typical lithium-sulphur prototypes can’t last more than a dozen or so charge-recharge cycles without losing it, “it” being their ability to store a charge.

The Berkeley solution was to develop a nanomaterial composed of small particles of graphene flakes coated with sulphur, namely S-GO. As described by Berkeley writer Allan Chen, S-GO is characterised by a large, cavity-speckled surface area, which allows for more “intimate electronic contact” with sulphur while minimising loss of contact with the current collector of the electrode.

When used as a cathode material in a lithium-sulphur battery, S-GO binds with lithium during discharge and releases it back to the anode during recharge.

Meanwhile, S-GO resolves some other key issues, including the massive bloating that bedevils lithium-sulphur technology. The graphene lends an element of flexibility that enables S-GO to accommodate the volume increase of up to 76 percent that sulphur suffers through as it is converted to lithium sulfide during discharge.

Now let’s take a look at how the S-GO cathode works together with other electrochemical technologies to extend EV battery range in a lithium-sulphur battery.

Aside from the vastly improved cathode performance, the new battery sports such goodies as an enhanced binder (elastomeric styrene butadiene rubber combined with a thickener) that increases power density.

To deal with the polysulfide issue, the team used a coating of cetyltrimethyl ammonium bromide (a surfactant commonly used in drug delivery systems) on the sulphur electrode.

Also helping out with the polysulfides thing was a new electrolyte based on an ionic liquid, developed in-house at Berkeley (ionic liquids are non-volatile and non-flammable).

The new ionic liquid also provides a huge boost in the rate of battery operation, while increasing the speed of charging and the delivery of power during discharge.

Here’s the result as reported by Chen:

The battery initially showed an estimated cell-specific energy of more than 500 Wh/kg and it maintained it at >300 Wh/kg after 1,000 cycles − much higher than that of currently available lithium-ion cells, which currently average about 200 Wh/kg.

That puts the new battery’s potential well within sight of a 300-mile (482-km) EV battery range:

For electric vehicles to have a 300-mile (482-km) range, the battery should provide a cell-level specific energy of 350 to 400 Watt-hours/kilogram (Wh/kg). This would require almost double the specific energy (about 200 Wh/kg) of current lithium-ion batteries. The batteries would also need to have at least 1,000, and preferably 1,500 charge-discharge cycles without showing a noticeable power or energy storage capacity loss.

The next steps include increasing the use of sulphur, maintaining performance in extreme conditions, and of course, scaling up to size.

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