Thursday, May 19, 2022

NREL researchers developing better behind-the-meter battery energy storage

The world has a huge challenge ahead of it to move net-zero by 2050 from a narrow possibility to practical reality. The transition will demand more from our electric grid than ever before. Stationary energy storage systems are critical to grid resiliency by ensuring that the power from renewable energy sources is available when and where it is needed.

Behind-the-meter storage (BTMS) systems directly supply homes and buildings with electricity and offer many advantages. The systems are designed to minimize costs and grid impacts due to their ability to integrate electric vehicle charging, photovoltaic generation, and building demands using controllable loads to generate and store energy on-site.

As part of the U.S. Department of Energy’s BTMS Consortium, researchers at the National Renewable Energy Laboratory (NREL) are leading the development of new high energy density lithium-ion (Li-ion) battery designs specific to the stationary storage requirements.

According to the researchers, BTMS systems have different charging and discharging patterns than a typical electric vehicle and require Li-ion battery materials that meet these unique priorities. These systems are expected to operate safely and efficiently over a long lifespan. Researchers looked at Li-ion battery designs using a Li4Ti5O12 (LTO) anode and LiMn2O4 (LMO) cathode, which are promising critical-material-free candidates that offer the safety and long lifespan required of BTMS systems. But these cells in conventional design have a comparatively low energy density.

The new research at NREL delved further into promising opportunities and limitations of using LTO/LMO battery cells for stationary storage use. NREL researchers evaluated the temperature-dependent performance of LTO/LMO cells with various electrode loadings. They determined that using thicker electrodes in battery designs can increase the cell capacity and energy density while decreasing overall cell costs.

However, these thicker electrodes require ions to travel a longer path, limiting the utilization of electrodes. They found that temperature adjustments can alleviate these negative impacts but may introduce added complications. The trick is to design a battery that offers the best balance for stationary applications.

Our goal with this research is to identify a ‘sweet spot’ to leverage the advantages of electrode loading and increased temperatures to maximize the performance of LTO/LMO battery cells,” said NREL Researcher and Project Leader Yeyoung Ha. “Our research refined material designs for BTMS specifically, converting this well-known power chemistry to energy cells.”

The NREL team further verified their findings by applying electrochemical modeling to simulate reactions at different temperatures and electrode thicknesses. They found that the electrode utilization was significantly improved by allowing batteries to have intermittent rest during discharge instead of being fully discharged as for electric vehicles. They also determined that this type of pulsed discharge is well suited for BTMS stationary applications, where the batteries will be used only when there is intermittent demand and then transitioned back to a resting stage.

Although these optimized LTO/LMO battery cells offer many advantages, the research team is also exploring cathode options that may better meet BTMS system needs.

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