Bipolar NiMHydride Battery

Electro Energy, Inc. (EEI) has developed a new type of rechargeable nickel-metal hydride (BP Ni-MH) battery using a bipolar configuration. A combination of unique materials, a design, and a production process make possible a lower cost technology which out-performs present commercial nickel-metal hydride and lithium polymer batteries in both power and energy.

A key advantage of a bipolar format is that the current path is the shortest possible. In a series arrangement, current passes directly through the separator, across its entire area. This eliminates the need for lugs and cell interconnections, with the additional internal resistance, sealing problems, and structure they bring.

The classic bipolar design (similar to most fuel cell stacks) involves a stack of metal plates, each with an anode applied to one side and a cathode to the other. For batteries, the problem of sealing the edges has proven difficult. EEI’s solution is to make each cell a stand-alone sealed flat wafer. The wafer cells are stacked up to make a higher voltage package.

EEI has developed and patented both the design of their battery and the production process for its manufacture. Prototypes exist and have been tested extensively. The US Air Force is evaluating units for use on F16 (and NAVAIR for the F18) jet fighters (1/3 the weight and volume of what they’re using now).

Conventional Ni-MH rechargeable batteries represent a $3 billion market currently, and EEI expects to dominate that and other markets, because their battery will deliver more energy and power per unit volume and per unit weight, at lower cost. Cycle life is in excess of 1000 cycles in deep discharge use, and over 12,000 cycles at 40% discharge. Cost will be 1/2 that of Li -Ion, and there are no toxics substances. The technology will be very competitive in the applications requiring high voltage and power, e.g. hybrid vehicles.

The company is seeking equity investment, having received over $15 million in government and other grants, particularly from DOD and DOE. A full business plan is available.

Contact: Mike Eskra, President & COO
Electro Energy Inc, Danbury CT

Cell Details
As a departure from classic cylindrical or prismatic battery packaging approaches, EEI’s is a flat, wafer, bipolar design for the nickel-metal hydride chemistry. Individual flat wafer cells have outer contact faces with one positive electrode, a separator and one negative electrode. The contact faces serve to contain the cell and make electrical contact to the positive and negative electrodes. The the two electrode faces are completely sealed at the edge to contain the potassium hydroxide electrolyte. To make a multi-cell battery, identical cells are stacked one on top of each other such that the positive face of one cell contacts the negative face of the adjacent cell resulting in a series-connected battery. Power is taken off at the ends of the cell stack. An outer container holds the cells in compression and provides structural integrity for the stack.

This design has several advantages. The need for conventional terminals, tabs, current collectors, and cell containers is eliminated. Use of available space is maximized, with the headspace for tabs and terminals required in conventional cells eliminated. The path that current has to move within the electrodes and from cell to cell is minimized, since the current flows out on the entire surface of the electrodes. Battery impedance is reduced, making this design particularly effective for high rate, power applications. The wafer stack has excellent thermal management properties. Cells act like cooling fins, conducting the heat out to the side. Compared to conventional cylindrical and prismatic packaging designs, there is considerable reduction in cost, weight, and volume.

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