The Bind BatteryTM is a system comprising a lithium ion battery and aqueous batteries such as lead-acid battery using CONNEXX SYSTEMS’ proprietary “Virtual Cell Hybrid System”(Patent No. 5373999). It is an innovative storage battery with safe overcharge protection mechanism and simpler charge/discharge controls, this is completely different from conventional lithium ion energy storage systems. It enables much simpler handling and continuous charging such as float charging like a lead-acid battery.
While a lithium ion battery provides high energy density and excellent life cycle, it has potential drawbacks of heat generation or ignition if overcharged exceeding a safety limit voltage, thus requiring a variable voltage control over charging with extremely high accuracy (at a level of several tens of mV). On the other hand, a lead-acid battery in principle is capable of dissipating an excessive energy by the electrolysis of the aqueous electrolyte, and therefore does not require a high accuracy control over charging unlike a lithium ion battery.
The Bind BatteryTM consists of a lithium ion battery and a lead-acid battery connected in parallel. When the lithium ion is overcharged producing excessive energy, the lead-acid battery absorbs the excessive energy and release the energy as heat, thus maintaining the lithium ion battery in a safe state. (Figure-(b))
Graph-(a) illustrates a test data that each of a lithium ion battery and the Bind BatteryTM was forcibly overcharged.
While the voltage of the lithium ion battery by itself continuously increased during charging and reached the unsafe voltage at the 5th cycle, that of the Bind BatteryTM did not increase beyond a certain value and returned to the original level during a pause, indicating that the state of overcharge was eliminated. As demonstrated herein, the lead-acid battery prevents the overcharge state of the lithium ion battery within the Bind BatteryTM without any external safety divices, enabling intrinsically sage mechanism against the overcharge with a simple configuration.
In general, a cell cost of a lithium ion battery is generally about 4 to 5 times as expensive as a lead-acid battery. In addition, peripheral equipment, such as a battery charger, tends to be more expensive for a lithium ion battery than for a lead-acid battery, since the lithium ion battery requires a high accuracy control and more delicate control and monitoring of the voltage, the current, and the temperature.
Usage of a low cost lead-acid battery in the Bind BatteryTM reduces the cost of the cells, as well as peripheral device cost due to a simplified charge control. Consequently, the Bind BatteryTM system makes the overall cost benefits much better than lithium ion batteries.
In general, while a lithium ion battery lasts 500 to 4,000 cycles in a JIS test, a lead-acid battery withstands merely an order of magnitude lower cycles when deep discharge is repeated. *Some deep cycle lead-acid batteries can last longer. Some are reported to last 4,000 cycles at 70% DOD.
In the Bind BatteryTM the lithium ion battery is designed to charge/discharge at higher voltage than that of the lead-acid battery. Thus, when the Bind BatteryTM is in use, it will discharge from the lithium ion battery portion and is stopped intentionally before the DOD of the lead acid increases in regular usage. If, however, more capacity is needed as in an emergency situation or at a lower temperature, the lead-acid battery can be tapped into by lowering the voltage. The controlled use, i.e. the limitation within low DOD of the lead acid battery extends cycle life of the Bind BatteryTM.
The Bind BatteryTM can be charged and discharged at below-freezing temperature when a lithium ion battery normally cannot function. As illustrated in Figure-(d) below, the Bind BatteryTM discharges at -20℃ while a lithium ion single unit battery hardly discharges (excluding some of lithium ion batteries).
| Lead-Acid Battery | Lithium ion Battery | Bind BatteryTM | |
|---|---|---|---|
| Cell Cost | ◎ | × | ◯ |
| Battery Life | × | ◎ | ◯ |
| Energy Density | × | ◎ | ◯ |
| Low Temperature Performance | ◯ | × | ◯ |
| Regenerative Charging Acceptance | × | ◯ | ◯ |
| Float Charge Support | ◯ | × | ◯ |
| High Safety | Connecting a Li-ion battery to a lead-acid battery eliminates ignition risk during overcharge and allows continuous charge including float charge and trickle charge. |
|---|---|
| Lower Cost | BMU and Protective Circuit normally attached to the Li-ion battery can be scaled down or simplified, leading to lower cost of the entire system. |
| High Performance | Based on the module of a general-use Li-ion battery and a lead-acid battery connected in parallel as the minimum unit, output, voltage, and capacity can be custom-designed in a simple configuration at a lower cost to meet a specific market or application. |
| Low Temperature Performance | A lead-acid battery portion can be charged and discharged at a low temperature where a Li-ion battery cannot perform. |
Table-(a) Comparison with Other Secondary Batteries
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