Blue Current’s Mission with Battery Safety and Performance
Blue Current’s Mission with Battery Safety and Performance
Blue Current’s mission is to build a battery that’s both inherently safe at the material level and delivers a big boost in energy density. The benefit of safety is self-evident. But customers will not pay extra unless they also get more performance. They care about how many hours their mobile phone lasts or how many miles their EV drives. Safety is assumed. But for manufacturers it has become a billion dollar financial and brand risk as battery failures become more common. The Chevy Bolt and Google Fitbit recalls in 2021 and 2022 are well known. In 2023, The FAA reported battery related incidents involving “smoke, fire, or extreme heat” virtually every week (see list of 90 events here) [2]. New York and San Francisco passed laws to reduce the number of e-bike explosions and fatalities. This author’s local sports shop burned to the ground after a rechargeable vacuum caught fire. It’s no surprise that we’re hearing from our industry partners that they want a battery that’s higher energy but also has lower probability of explosive thermal runaway in the case of a cell failure.
Given the inherent risk with traditional lithium-ion batteries, engineers must design safety at the system level with added complexity and cost. In a mobile device this includes a few sensors and a monitoring chip. But in an EV the overhead is higher. Consider that a 1000-pound EV battery pack contains the energy equivalent of 35 kg (175 sticks) of TNT [Note 1]. The World Electric Vehicle Journal reports that volumetric energy density for an EV is reduced by a factor of three going from cell to module to pack. It shows that the highest cell energy densities were 750 Wh/L but at the pack level it’s only 250 Wh/L [Figure 1]. Much of this is due to the overhead for safety including added space between cells, fire-resistant packaging materials, hundreds of sensors, complex liquid thermal management systems, and computerized controls. Fire-retardant foam alone can cost over $300 per pack and the overall system cost for adding safety can be over a thousand dollars per car.
Figure 1: From Cell to Battery System in BEVs: Analysis of System Packing Efficiency and Cell Types. World Electric Vehicle Journal, 2020 [1]
To reduce risk, EV companies are shifting to cylindrical cell designs which have built-in safety mechanisms but lower overall system energy density versus pouch or prismatic cells or to LFP that has 40% lower energy density (and cost) but higher safety. While manufacturers are challenged to engineer safety into their products the battery industry is exploring higher energy chemistries that may only make the problem bigger. For example, there are many companies focusing on lithium metal that’s highly reactive and flammable with air, and engineered silicon (Si) that packs more energy into a smaller space containing flammable liquid electrolytes.
Starting in late 2014, Blue Current focused on developing a liquid electrolyte that could dissolve lithium salts for ionic conductivity and was non-flammable with the goal of achieving an inherently safe battery chemistry. But we found it to have poor conductivity and it was also no less explosive than traditional lithium-ion batteries with flammable organic-liquid-based electrolytes. In 2016 we pivoted to using fully dry composite electrolytes with higher conductivity and thermal stability. In 2018 we added silicon active materials which increased energy density. We call this combination the silicon elastic composite battery system. This is the technology we’ve been working with ever since. We’ve done nail, crush, and over charge testing on small multi-layer cells and we see no thermal runaway or violent ejection of battery materials. Additional ARC and DSC tests show that the cells are thermally stable at high temperatures. We are encouraged by our results, and we plan to continue safety testing as we produce larger cells in our new pilot factory. Over time we expect this approach to deliver greater safety and a big boost in performance that will enable simpler, lower cost, and more capable products.
[Note 1] Calculation based on the equivalent of a Tesla Model S battery pack with 7104 x 18650 cells. Each 18650 has the 5.57g of TNT-equivalent. See the following article: Thermal runaway hazards investigation on 18650 lithium-ion battery using extended volume accelerating rate calorimeter
1 – Löbberding, H. et al., From Cell to Battery System in BEVs: Analysis of System Packing Efficiency and Cell Types. World Electric Vehicle Journal, 2020.
2 – Lithium Battery Air Incidents. Federal Aviation Administration, 2023.
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