State-of-the-art (SOA) Li-ion batteries (e.g., with graphite anode and LiCoO₂ cathode) for consumer electronic devices (e.g., cell phones, laptops) are designed to operate at a certain voltage range, e.g., 3-4.2V [1]. When an electronic device, like a cell phone, indicates “low battery”, the battery is near its low operating voltage threshold, and soon the device may automatically shut down to prevent the battery from further use (discharge). If a SOA Li-ion battery is allowed to further discharge to a very low cell voltage, e.g., near 0V, the battery will deteriorate quickly, manifested with a reduced battery capacity (electric charge, Ah), i.e., reduced battery use time. This is because, at or near 0V, the anode potential can exceed the substrate (commonly Cu) dissolution potential, which results in corrosion of the Cu substrate (pittings, holes) leading to compromised battery performance [2]. 

A battery capable of 0V (or near 0V) storage is desirable as it overcomes irreversible battery performance losses from self-discharge (to a very low voltage). For this reason, SOA Li-ion batteries are maintained above a certain threshold, e.g. > 20-30% capacity. For large format Li-ion batteries/packs, the energy left inside batteries at storage can cause serious concerns regarding: (i) safe battery transport, (ii) high maintenance cost (monitoring and periodically charging the batteries) and (iii) safe battery storage. Li-ion battery safety is a real issue exemplified by the recent Boeing 787 battery [3].

Prior art to remedy Li-ion battery at or near 0V storage includes the use of an anode substrate with a higher dissolution potential, e.g., Ti substrate [4]. However Ti current collectors possess shortcomings including high cost of the Ti current collector and poor electrode coating adhesion on Ti substrate. Moreover, fundamentally, for a graphite-based anode, a solid-electrolyte-interface (SEI) film formed on graphite anode (due to organic electrolyte reduction) can break down at or near 0V and adversely impact battery performance and life.

Here we present a novel approach to develop a high performance Li-ion battery, capable of deep discharge and/or storage near 0V. Our anode active material selection criterions include: (i) amenable to substrates with high dissolution potentials, (ii) sufficient (electrical) potential to avoid SEI film formation and (iii) high specific capacity for battery high energy density. Our cathode active material selection criterions include high specific capacity and high voltage to achieve high battery specific energy. Other criterions common to the anode and the cathode include high rate capability and robust cycle life.

Figure 1 shows cell capacity retention as a function of cycle number for ADA near 0V capable Li-ion cells. The cells were stored at ~ 0V for 2 days for every 5 cycles. The control cell was cycled without low voltage storage. After accumulative storage for 30 days at 50mV and 100mV, respectively, the ADA near 0V capable cells demonstrated little or no capacity fade, comparable to the control cell. We attribute the excellent cell deep discharge/storage resilience to our near 0V tolerant electrode material selections.

For comparison purposes, we applied the identical test conditions to graphite based Li-ion cells as shown in Figure 2. The graphite based Li-ion cells experienced rapid capacity deterioration (i.e., capacity drop to zero) after a short period of ~ 0V storage. This is likely due to Cu current collector dissolution and dissolution/reformation of SEI films on graphite anode.

Our study showed that this battery technology is a very promising high performance and safe power source capable of long-term ~ 0V deep discharge/storage. This battery technology is being developed for applications in the transportation, consumer electronics, military and space markets. 

References

1. "Lithium Ion technical handbook". Gold Peak Industries Ltd. November 2003.

2. Rui Guo, Languang Lu, Minggao Ouyang, and Xuning Feng, Scientific Report, 2016; 6: 30248.

3. National Transportation Safety Board Report, Case No. DCA131A037, March 7, 2013.

4. Hisashi Tsukamoto, Clay Kishiyama, Mikito Nagata, Hiroshi Nakahara, Tiehua Piao, US6596439.