The lithium-ion battery is currently the dominant energy storage device best suited to meeting these demands, with manufacturers looking to enhance the overall performance of the battery pack with new cell chemistries, construction, and formats, including hybrid-batteries.
Two patents describe StoreDot’s "hybrid battery packs" consisting of two different cell chemistries that support the configuration of a fast-charging battery to emulate a supercapacitor and also enable adaptive fast-charging for mobile devices and devices with sporadic power-source connection.
Taken together, these two patents define a novel approach of combining different cell chemistries within a battery to enhance the overall parameters of the Li-ion battery pack.
Batteries store energy electrochemically through chemical reactions that release electrical carriers that can be absorbed into an electrical circuit. In Li-ion batteries, during charge and discharge cycles the energy-containing lithium ions travel to and from the high-energy anode and the low-energy cathode materials, respectively, passing through a separator.
Even though Li-ion batteries have the highest energy density of rechargeable batteries available, they typically suffer from low power by virtue of reversible Coulombic reactions occurring at both electrodes, involving charge transfer and ion diffusion in bulk electrode materials. Since both diffusion and charge transfer are slow processes, power delivery as well as the recharge time of Li-ion batteries is kinetically limited. As a result, batteries have a low power density, and lose their ability to retain energy throughout their lifetime due to material degradation.
On the other hand, electrochemical double-layer capacitors or ultracapacitors make up, together with pseudocapacitors, a new type of electrochemical capacitor called supercapacitors (referred to as SCs), which store energy through the accumulation of ions on an electrode’s surface. Although these devices have a limited energy storage capacity, they exhibit excellent power density.
In the SC, energy is stored electrostatically on the surface of the material, and does not involve a chemical reaction. As a result, a SC can be charged quickly, leading to a very high power density without a loss of storage capability over millions of charge/discharge cycles. The main challenge facing the SC is its low energy density, meaning that the amount of energy stored per unit weight is very small, particularly when compared to a Li-ion battery.
So although it would seem to make sense to combine the high energy and high power density of the LiB and SC in a single device, so far such hybrid power-source devices have mainly been limited to parallel connection (i.e., an SC used as a power supply, with the battery used as an energy source, which supplies energy both to the load and to the SC, which in turn, should be charged at all times). In this configuration, performance is limited by the minimal use of the SC, and the higher degradation of the battery due to the additional charging of the SC.
It is for this reason that StoreDot’s patent defines a method to configure a fast-charging battery to emulate a supercapacitor with given specifications by operating the fast-charging battery only within a partial operation range which is defined according to the given specifications of the supercapacitor - being smaller than 20 percent, possibly 5 or 1 percent, of a full operation range of the fast-charging battery.
Devices are proposed that comprise control circuitry and a modified fast-charging lithium ion battery, such as the XFC, having Si, Ge and/or Sn-based anode active material and designed to operate at 5 C at least and within a range of 5 percent at most around a working point of between 60 to 80 percent lithiation of the Si, Ge and/or Sn-based anode active material, wherein the control circuitry is configured to maintain a state of charge (SOC) of the battery within the operating range around the working point.
In conjunction with this patent StoreDot has another invention that describes systems and methods for adaptive fast-charging of mobile devices and devices with sporadic power-source connection. These methods consist of multiple steps: firstly determining whether a supercapacitor contained in a device is charged; if the supercapacitor is charged, the next step is to determine whether the device’s battery is charged. If the battery is not charged, it is firstly charged from the supercapacitor. Preferably, the SoC of the supercapacitor and battery will be determined before charging takes place.
Ideally, charging will be regulated such that it preserves the lifetime of the battery by controlling the current to the battery when discharging the supercapacitor to charge the battery. Preferably, the discharge must allow the supercapacitor to be recharged.
It is envisaged that the XFC cell maybe optimized to operate as a supercapacitor providing the battery pack with a much higher lifetime
When pairing a normal Li-ion cell with an XFC cell in a hybrid battery pack such a pack would be ideally suited to applications where the current infrastructure is enough to charge the whole pack, with the XFC battery always ready to be charged. Because of the XFC cell’s high-C capabilities, such a hybrid battery would be ideally suited to efficiently utilize regenerative energy converted from kinetic energy.
In such applications the XFC cell would put less stress on the "standard" battery, resulting in cost saving through implementing cheaper "standard" technology, thereby reducing total cost of ownership. This would allow the standard battery to "always be charged" and ready for long range use cases.