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Fast Charge Silicon Anode Lithium-Ion Cells for Small UAS Systems

Description:

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Renewable Energy Generation and Storage, Advanced Materials

 

OBJECTIVE: Fast charge silicon anode lithium-ion cells for small UAS systems.

 

DESCRIPTION: The ability to fast charge (less than 6 minutes) commercial graphite anode Li-ion cells to specific energies greater than110 Wh/kg is a significant challenge. The inability to fast charge to higher specific energy means that more batteries must be in the logistics chain to supply operations and that onboard/critical edge charging is not an option for many fast-paced operations. A promising technology that is currently being developed for high energy Li-ion cells (300-400 Wh/kg) is based on silicon (Si) anodes that have demonstrated fast charge capability in prototype cells.  The challenges with Si anode cells are cycle life, calendar life, and safety. Many Si anode cell developers are focused on achieving the highest energy batteries and not on the ability to fast charge with long cycle or calendar life.

 

Cell capacity, safety, and cycle life typically suffer when Li-ion cells are charged quickly with the limitations mainly relating to the graphite anodes inability to absorb lithium ions without plating lithium metal. Si anodes alloy with lithium and demonstrate capacities 10X that of graphite at a potential and electrode thickness that make lithium plating much less likely under fast charge. Si anode cycle life is lower than commercial graphite systems due to several factors including the mechanical grinding of the Si alloy under repeated cycling that leads to loss of active material contact as well as the continuous new surface generation and subsequent passivation that occurs as the Si swells and contracts upon charge and discharge. Calendar life is poor in these systems which limits its use in EV applications, but for several specialty applications, the specific energy provides much needed capability.

 

Energy sharing between energy sources (vehicles, generators, solar chargers) and Soldiers already occurs when BB2590 batteries are charged in the field. The charging process is slow and often it is easier to swap batteries if available. Fast charge batteries are part of the DEVCOM Army Research Laboratory VICTOR (VERSATILE TACTICAL POWER AND PROPULSION) Essential Research Program and in tandem with wireless recharge and silent power generation, will eliminate battery swaps, reduce the cognitive and physical load on Soldiers, and reduce the logistical tail in batteries. One example is the use of fast charge batteries in small unmanned air systems (sUAS) charged from mobile ground stations that enable autonomous recharge, freeing the Soldier from carrying and changing batteries, and reducing their exposure on the battlefield.

 

This topic seeks the development of Si based fast charge cells with demonstrated specific energy greater than 200 Wh/kg in 6 minutes of charge in order to enable new concepts in energy sharing, increased pace of operations, and compact energy sources for high power devices. This topic looks to have Si anode materials brought further into development and to demonstrate the improvements in full Li-ion cells for use in VICTOR ERP programs.

 

PHASE I: In the phase I effort, demonstrate single/few layer Si anode full cells that when fast charged at 10C (6 minute) rates, cycle for >1000 continuous cycles at 3C discharge to > 80% capacity.  These cells should support the development of multi-Ah cells with a specific energy > 200 Wh/kg.  Deliverables would be 10 full cells of >100 mAh capacity capable of 10C charge / 3C discharge and >1000 cycles to > 80% capacity.

 

PHASE II: Phase II would involve producing and characterizing cells in sufficient quantities to fully characterize them for rate, temperature performance, and continuous cycling stability. Deliverables include 20 full cells at a rated capacity of > 2Ah capable of 10C/3C charge-discharge cycling at an energy density of >200 Wh/kg at the 10C charge rate.

 

PHASE III DUAL USE APPLICATIONS: The applications where this technology could be used include storage for high energy storage modules (HESM), jammer applications, 6T battery applications, and for fast charge batteries in UAS systems. Commercial applications include batteries for hybrid electric vehicles and eVTOL. Likely sources of funding if the phase III program is successful include PEO Soldier, PM UAS, and C5ISR.

 

REFERENCES:

  1. Inorganics 2023, 11(5), 182; https://doi.org/10.3390/inorganics11050182;
  2. Nature Nanotechnology, volume 3, pg 31–35 (2008);
  3. https://amprius.com/technology/;
  4. https://arl.devcom.army.mil/what-we-do/victor/

 

KEYWORDS: Fast charge, Lithium-ion, Silicon anode, High power

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