A family of Tesla patents and pending applications relating to a hybrid battery system has been generating a bit of buzz (see, e.g., Cleantechnica’s story here).
The patent family includes U.S. Patent Nos. 8,190,320, 8,450, 974, 8,471,521 and 8,543,270 as well as U.S. Patent Application Publication Nos. 2013/0181511 (‘511 Application) and 2013/0187591 (‘591 Application), some of which are entitled “Electric vehicle extended range hybrid battery pack system” and others entitled “Efficient dual source battery pack system for an electric vehicle” (collectively, “Hybrid Battery Pack Patents”).
Some of the applications were filed back in 2010, and some of the patents issued in 2012. The Cleantechnica piece refers only to the ‘511 and ‘591 Applications, which published in July, because these applications apparently were cited in a recent report by Global Equities Research.
The Hybrid Battery Pack Patents are directed to methods of extending an electric vehicle’s driving range through a discharge cycle (201) using energy paths (203, 204) flowing from two battery packs, one being a metal-air battery pack (101) and the other being a non-metal-air battery pack (103), presumably a lithium ion battery.
Controller (107) controls the flow of energy to and from both the metal-air battery pack (101) and the non-metal-air battery pack (103). The methodology applied by the controller (107) is based on input from a variety of sensors (211) as well as the current operating conditions such as temperature and state-of-charge (SOC) of both battery packs.
One example of the methodology can be seen in FIG. 3 of the Hybrid Battery Pack Patents, in which the metal-air (MA) battery pack is used to charge the non-metal-air (NMA) battery pack when the SOC of the NMA battery pack falls below a preset value.
This is consistent with the Cleantechnica article, which notes the patents’ mention of a mode whereby the metal-air battery woudl charge the lithium-ion battery. The article says the hybrid battery pack would primarily use the lithium ion battery and draw power from the metal-air battery only on extended journeys.
From the patents’ summary section:
The present invention provides a power source comprised of a first battery pack (e.g., a non-metal-air battery pack) and a second battery pack (e.g., a metal-air battery pack), wherein the second battery pack is only used as required by the state-of-charge (SOC) of the first battery pack or as a result of the user selecting an extended range mode of operation.
The Hybrid Battery Pack Patents note that metal-air batteries have certain advantages over conventional rechargeable batteries such as extremely high energy density, but they also have drawbacks like electrolyte evaporation and the need to ensure sufficient air supply. By combining a metal-air battery with a lithium ion battery, the hybrid system takes “advantage of the benefits of both battery types, while significantly limiting the negative effects of either type.”
Cleantechnica calls this a “different kind of hybrid” and says “[a] hybrid battery of this type could offer Tesla customers greater driving ranges, while not drastically increasing costs.”