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Fail-Safe Design for Large Capacity Li-Ion Battery Systems

National Renewable Energy Laboratory

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Technology Marketing Summary

Lithium-ion batteries (LIBs) are a promising candidate for energy storage of electric drive vehicles due to their high power and energy density. The total electric vehicle LIB market shipped 2,400 units in 2008 generating over $28 million in revenue and is predicted to be greater than $10 billion by 2015. However, violent incidents reported for LIBs and consequent safety concerns pose a major obstacle to LIB market acceptance. Safety mitigation technologies used in small capacity consumer product LIBs are not effective in large capacity LIBs as the scale up process dramatically changes the responses of the LIB system under safety incidents. Robust early detection of faulted unit cells, together with isolation of those cells from a multi-cell pack, are difficulties that must be overcome to clear the safety hurdle of large scale LIBs.

 In conventional LIBs, electrode particles are mixed with conductive agent and pasted on highly conductive metal current collector sheets. While charge transfer reaction occurs at the active particle surfaces, the electric current is carried by current collectors from or into the LIB cell. Electrical pathways in LIBs accomplish two distinguished roles. First, they deliver battery electric power during charge and discharge of a LIB system. Second, they keep balance within a LIB system to maximize material utilization and to prolong life.

NREL scientists have invented a new fail-safe battery design for large-capacity cells and multi-cell packs which separates the roles of electrical current pathways, enabling robust fault detection, isolation, and improved effectiveness of safety mitigation technologies popular in small capacity LIBs.


In a typical battery cell, all electrode sub-regions of the cell are internally connected in parallel. These parallel connections are generally designed to have very low resistance in order to maximize cell discharge/charge performance and maintain good cell-internal balance. This is especially true for high power large batteries where the ohmic resistance of current collectors must be minimized to carry large amount of discharging and charging current without excess ohmic loss.

While it is important that the current collectors provide low resistance pathways for charge/discharge current to flow to/from the cell, the same is not true for cell balancing current. Cell balancing current doesn't need to be carried with low resistance conduction path, since this current is much smaller than the cell charge/discharge current for supplying electric power.

Recognizing this, the concept of the invention has discrete multiple electrodes. Each discrete electrode is connected in series to a separate positive or negative terminal through a highly conductive current path. Those multiple terminals are connected in parallel through relatively high resistance conduction paths (likely) outside the cell to carry small current for cell balancing. This design addresses the problems regarding large LIB safety issues, including robust fault detection and faulted cell isolation, and is applicable at both the single-cell-level and multi-cell pack-level.

  • Early fault detection
  • Fault isolation
  • Can work on single-cell-level and multi-cell pack-level
Applications and Industries
  • Electric vehicles
  • Grid Storage
  • Defense
  • Aerospace
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 9,341,678
Fail-safe designs for large capacity battery systems
Fail-safe systems and design methodologies for large capacity battery systems are disclosed. The disclosed systems and methodologies serve to locate a faulty cell in a large capacity battery, such as a cell having an internal short circuit, determine whether the fault is evolving, and electrically isolate the faulty cell from the rest of the battery, preventing further electrical energy from feeding into the fault.
National Renewable Energy Laboratory 05/17/2016
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL 11-69 DevelopmentAvailable04/25/201204/25/2012

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To: Erin Beaumont<>