Novel Energy Storage System, bindbattery™, with an Intrinsic Overcharge Protection Capability
Authors: Tamaki Ryo , Tsukamoto Hisashi 
Published: February 2020

CONNEXX SYSTEMS developed a novel hybrid energy storage system, bindbattery™, with a unique overcharge protection capability, high power and high energy capability and long cycle life at low cost without complex battery management system. bindbattery™ consists of lithium-ion battery units and aqueous electrolyte battery units. The two units are connected in parallel and form a virtual cell. The multiple virtual cells are connected in series and in parallel to meet specifications of each application. An aqueous electrolyte battery could be chosen from a nickel-hydride battery, lead-acid battery or other form of aqueous batteries depending on requirements of applications. Hybridization with an aqueous electrolyte battery makes bindbattery™ tolerable to abusive conditions such as reverse directional high current pulse or overcharge current. Benefits of bindbattery™ include: 1) Safety: The lithium-ion battery is protected from the devastating overcharge by aqueous batteries connected in parallel. The aqueous battery unit consumes overcharge energy through the aqueous electrolyte decomposition (electrolysis). The oxygen evolved at the positive electrode recombines with hydrogen on the negative electrode and reforms water. By connecting the lead-acid battery and lithium-ion battery in parallel, the lead-acid battery effectively protects lithium-ion battery from overcharge by absorbing the overcharge current through the chemical reaction. Thus, bindbattery™ does not require complex electronic protection circuit to protect from overcharge. In other words, the bindbattery™ configuration makes the battery system intrinsically safe. This simplifies construction of the bindbattery™, and reduces both the cost and the weight and makes the battery suitable for large scale stationary applications. 2) Power performance: As a result of high power characteristics of both high power lithium-ion batteries and lead-acid batteries, bindbattery™ has a high power capability. 3) Cycle life improvement: The lead-acid battery is an inexpensive battery but its cycle life is poor compared to the lithium-ion battery. The lithium-ion battery has higher discharge voltage than the lead-acid battery, therefore lithium-ion battery discharges prior to the lead-acid battery in bindbattery™. Thus bindbattery™ provides an excellent cycle life in the same manner as the lithium-ion battery. 4) High energy density: bindbattery™ can provide a larger energy compared to the lead-acid battery alone as a result of the hybridization with lithium-ion battery. 5) Low temperature
performance improvement: The lead-acid battery has excellent low temperature capability. At subzero temperature, lithium-ion battery is not able to discharge immediately. In bindbattery™, the lead-acid battery discharges first and provides warm-up time for the lithium-ion battery. 6) Float charge capability: Like other aqueous batteries, bindbattery™ can be used in the float-charge mode. 7) Cost improvement: Use of lead-acid battery as an aqueous battery units lowers the cost significantly. Elimination of electrical protection switches and battery management units contribute to the cost reduction. These unique features make bindbattery™ the most suitable energy storage system for stationary applications including storage system for renewable energy, demand shifting and frequency regulation. We developed 20 kWh bindbattery™ module for stationary applications such as solar energy or wind energy storage. The module will comprise a larger scale storage system by connecting multiple of the modules in parallel or in series. The simplified control method and low cost also make bindbattery™ a remarkable choice for car applications.