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Overcharge Protection for Lithium-ion Rechargeable Batteries





Berkeley Lab scientists Guoying Chen and Thomas J. Richardson have invented a new type of separator membrane that prevents dangerous overcharge and overdischarge conditions in rechargeable lithium-ion batteries. This low cost separator, with electroactive polymers incorporated into a porous fiber membrane, provides electronic insulation and high ionic conduction during normal cell operation, enabling high charge and discharge rates for high power density.

In overcharge and/or overdischarge situations, the membrane provides a reversible, self-actuated current shunt to prevent damage to the battery. By allowing other cells in the pack to continue charging, these separators balance the charge on each cell to extend battery life and use all of the available capacity.
The threshold voltage for these membranes can also be tuned for different battery chemistries by using different electroactive polymers. Batteries incorporating such membranes thus have higher rate capability, improved safety, and longer cycle life.

When overcharged, battery safety issues including overheating, explosion, and fire may arise. Even slight overcharging reduces a cell’s discharge capacity, leading to overdischarging, which increases impedance and heat generation, and decreases cell lifetime. Yet common approaches to preventing overcharge / overdischarge all have drawbacks. For example, external electronic controls add substantial weight, cost, and complexity to a battery pack. Shutdown separators that melt at ~160°C permanently disable the cell, increasing the strain on the remaining cells. Redox shuttle additives have limited sustainable current densities and cell charging rates, and do not work well at the low temperatures commonly experienced by vehicles. The Berkeley Lab overcharge protection technology overcomes limitations observed in other approaches.

Caption: The LBNL-developed separator membrane provided long-term reversible overcharge protection for this lithium-ion cell, even after hundreds of continuous, full charge/discharge cycles over more than 1770 hours of operation.


G. Chen and T. J. Richardson, “Overcharge Protection for Rechargeable Lithium Batteries Using Electroactive Polymers,” Electrochemical and Solid State Letters, 7, A23 (2004).

G. Chen and T. J. Richardson, “Overcharge Protection for 4 V Lithium Batteries at High Rates and Low Temperatures,” Journal of the Electrochemical Society, 157, A735 (2010).

STATUS: Patent pending. Available for licensing or collaborative research.


Non-Cross-Linked Gel Polymer Electrolytes for Lithium Ion Batteries, JIB-2731

Conductive Binder for Lithium Ion Battery Electrode, IB-2643

Silicon Composite Electrode for Advanced Lithium Ion Battery, IB-2890


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Last updated: 09/27/2012