Eos Insights: Imitation Is the Sincerest Form of Flattery, Right?

Building the Eos Z3? Battery by Francis Richey , Sr. VP R&D

Inspiration can often come from a close examination of great ideas that, for any given reason, might not have worked in their first iteration or attempt. Certainly, that is the case for zinc halide batteries. While the original flow battery design was abandoned by Exxon in the early 1980s, many aspects of that design served as inspiration for the Eos Z3? battery.

?Eos’s goal from the beginning was to design and manufacture a simple-to-operate and extremely abuse-tolerant battery system, while also targeting a scaled commercial product with a low cost of ownership. With such lofty ambitions, we knew this could only be met with revolutionary technology improvements to known and proven battery chemistries to get us there quickly.

?Originally patented in 1983, we took inspiration from Exxon’s zinc halide flow battery design to create our Eos Z3? battery. The Exxon framework guided us toward a static bipolar module that reduces operating costs, simplifies the overall design, and eliminates pumps and membranes that were required in the original flow batteries. This was key in developing an efficient and profitable battery storage system that can better serve grid-scale applications.

?However, this was no small feat. Teams of engineers and scientists studied the original flow battery and spent seven years iterating and building on the basic chemistry of the battery to develop a static zinc halide design.

?Though different from the original Exxon flow battery in many ways, the evolution of the technology is evident in various aspects of the Eos Z3? battery. In a static battery, engineering the electrolyte composition and cathode surface area to take advantage of natural convection within the cell during operation is critical to improve performance.

?As an example, Eos now utilizes a hybrid electrolyte consisting of mixed chloride and bromide electrochemistry in the Z3 – an elevation of the original bromide/bromine electrochemistry. This improvement has increased cell voltage and energy, and reduced electrolyte cost. Fun fact, the Eos technical team has tested over 1,300 different electrolyte formulas in over 27,000 individual cells to optimize component performance. Testing and iterating at this scale allowed Eos to more than double energy density (50 Wh/L to 105 Wh/L) while maintaining energy efficiency, which significantly reduces system cost and footprint.

?The Exxon patents also inspired Eos to transition from titanium current collectors to conductive plastic current collectors in the Eos Z3? battery module. The plastics processing industry has significantly improved their ability to extrude highly filled plastic materials over the past few decades, which has allowed for highly conductive plastic materials to be developed and scaled at significantly lower cost. As we developed conductive plastic current collectors specifically for our Eos Z3? battery, we worked closely with SABIC Specialties. This collaboration recently won a Gold Edison Award for the conductive plastic materials currently being used in our battery.

?The result of all this work is a long-duration, 4-12+ hour discharge intraday usage battery energy storage system (BESS) that provides a stabilizing force to our aging grid system in the U.S. It provides greater reliability and resiliency to the grid, no matter the energy source. Best of all, it does so with a non-flammable battery, ease of transport and shipping, ease of implementation and registering at fewer than 60 decibels, virtually no sound issues.?

?All the materials in the Eos Z3? battery are recyclable and made up of over 90% U.S. domestic content. ?There is no calendar degradation in the Eos batteries, and system balancing is considerably easier than incumbent technologies due to our proprietary State of Charge (SoC) and State of Health (SoH)?algorithms and the ability to passively rebalance. Since the Eos electrodes do not mechanically expand and contract during cycling, there is minimal energy degradation over the life of the product, minimizing the need for expensive augmentation and repowering.

?Today, our technology is covered by over 100 patents from electrochemistry to cell design, to module and system, and Battery Management System (BMS)?software. Our patent strategy is simple: protect from the base chemistry upwards.?This allows us to meet our primary goal of protecting the core of Eos’s products.

?That was our main concern for the first 10 years of Eos’ history. For the last six years and into the future of the company, we are now laser focused on cell material improvements, scaling manufacturing, and improving our supply chain to drive down costs and improve battery performance.