Novel Operational Strategies to Enhance Battery Performance: Acoustics
part 2 of optimising battery performance
How a battery performs very much depends on not just how it was made, but how it is treated. Move over heat and pressure from part 1, there are new talents in town: today we look at Acoustics!
While the role of heat and pressure on impacting battery performance has been researched for decades now, new operational techniques are emerging to improve battery performance. We will focus on two of these technologies, magnetism and acoustics, that are primarily focused on improving ion transport throughout the electrode stack to enable fast charge/discharge with good capacity retention.
Interestingly, the secondary impact of improved ion transport is also good reaction kinetics due to sufficient active ion concentration at the electrode-electrolyte interface. In traditional lithium-ion batteries, ion transport is primarily via diffusion (due to concentration gradients) and migration (due to potential gradients). Acoustics provide extra driving forces in addition to these mechanisms.
Acoustics
Recently, surface acoustic wave devices (SAWs) have been identified as technology that can induce acoustic streaming-driven fluid-flow up to 1m/s. They consist of a piezoelectric substrate with interdigitated electrodes through which current is passed.
Piezoelectricity is the phenomenon where certain materials (e.g. quartz) generate an electric charge in response to applied mechanical stress, or conversely, deform in response to an electric field. In SAWs, the associated electrical energy is transformed into mechanical energy which generates surface acoustic waves in a process known as actuation.
This is bulk electrolyte flow which essentially stirs the liquid together to mix the ions well.
So, SAWs can be used to impart bulk electrolyte flow inside batteries which helps in alleviating ion concentration and potential gradients inside the liquid phase. Advection plays a key role alongside diffusion and migration to transport ions. The high density of active charged ions at the interface also translates to improved reaction kinetics at the electrode-electrolyte interface.
Huang et al. demonstrated the application of a 100 MHz surface acoustic wave device to enable operation of a Li|Cu cell. The experiment involved deposition of lithium onto the copper substrate until a capacity of 1 mAh/cm2 was reached at different current rates with and without SAW device. Current rates of 6 mA/cm2 could be sustained with the help of a SAW device without short circuit. In contrast, the baseline cell without SAW failed by short circuit at a current of 2 mA/cm2. This signifies a near three-fold increase in performance. Furthermore, dendrite-free dense Li deposits are seen with SAW while dendrites and porous Li are observed in the baseline cell.
Another interesting observation is that SAW’s are most impactful at high current rates. This is because at low current rates < 1C, the concentration and potential gradients inside the electrolyte are minimal, so circulating the electrolyte further is not going to improve the performance much. So, this technology is well suited to work with high power cells (think EV batteries) as compared to high energy cells (think laptop/phone batteries).
What companies are in this space?
Sonocharge, based in San Diego, California, USA and led by CEO An Huang, is developing piezoacoustic platforms to embed with batteries and improve battery performance. A patent granted in 2024 showcases the arrangement of an acoustic wave device at the bottom of a flat prismatic cell to generate electrolyte flow.
Steady discharge capacity with cycling is observed with the SAW device for up to 160 cycles for an unidentified battery configuration while the baseline battery fades rapidly to 20 mAh/g within 100 cycles.
Furthermore, Sonocharge has recently won an ARPAE Circular award to demonstrate the application of surface wave technology in extending the life of battery cells. This project is aimed at rejuvenating cells through electrolyte replenishment; old electrolyte removal and new electrolyte flushing through clogged pores of a used battery can be facilitated by agitating the electrolyte with SAW device.
In the next part, we will take a look at Magnetism…
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