(Invited) Safety Behavior of Lyten’s High-Energy Li-S Cells with 3D Graphene™
Authors: Bugga Ratnakumar 
Published: February 2024

Safety Behavior of Lyten’s High-Energy Li-S Cells with 3D Graphene™

Ratnakumar Bugga, Celina Mikolajczak, Zach Favors, Karel Vanheusden, Arjun Mendiratta, Jefferey Bell, Penchala Kankanala and Dan Cook

Lyten Inc., 145 Baytech Dr., San Jose, CA 95134

Lithium-sulfur (Li-S) batteries are the leading candidates in the next generation high energy systems to supplement or supplant the conventional Li-ion batteries (LIB) in commercial and DoD applications. Unlike other high energy systems with NMC cathodes, Li-S chemistry has the distinct advantage of being unaffected by the criticality and scarcity of raw materials (e.g., Co and Ni), which can pose significant challenges for robust supply chain and stable pricing. Li- S cells can potentially offer 2-3-fold higher specific energy compared to LIBs at significantly lower cost and have better compliance with environmental regulations,1 as well as, a significantly reduced carbon footprint. Despite their numerous advantages, the implementation of Li-S batteries in practice has been impeded by their classic problem of ‘polysulfide (PS) shuttle’, which is a result of PS dissolution in liquid electrolyte, and is a primary cause of poor cycle life.2

Lyten, an advanced materials company founded in 2015, has developed Lyten 3D Graphene™ (3DG) from methane cracking that has a mechanically flexible and electrically conductive framework to counter the volume expansion and low conductivity of sulfur, and a tunable hierarchical porous structure to confine sulfur and PSs and restrict them from shuttling to the Li anode. Lyten has been developing high energy and long-life Li-S cells based on these high-performance, nano-porous carbons. By further optimizing these 3DG materials microstructurally and chemically,3 Lyten has developed sulfur cathodes far superior to those containing commercial nano-porous carbons traditionally used in Li-S cells. In parallel, Lyten has been developing robust Li anodes with protective coatings, advanced electrolytes with reduced PS solubility, separator coatings for low polysulfide crossover, cathodes with low binder, high sulfur loadings and high areal capacities, and high-energy cell designs with minimal excess anode capacity (low N:P ratio) and low quantities of electrolyte (low E/S ratio). These advances have culminated in Lyten Li-S cells with high specific energy (275 Wh/kg), on par with current Li-ion cells, and a cycle life of ~300 cycles @C/3 in coin cells and ~150 full DOD cycles and >1200 during partial cycling in multi-layer pouch (MLP) and cylindrical cells.

Another notable advantage of Lyten Li-S cells is their superior abuse tolerance, compared to LIBs, during electrical, mechanical, and thermal abuse. Though Li-S cells, like other Li metal batteries, are suspected to be less safe due to metallic Li, the safety of Lyten Li-S (1.5 Ah) multi-layer pouch and 18650 cylindrical cells has been demonstrated in our preliminary abuse tests (Fig. 1), i.e., nail penetration simulating internal short, external short, overcharge, over-discharge and mechanical crush test. There is no flame, smoke, charring, rupture, or thermal runaway in any of these abuse tests, underlining the innate safety of Lyten Li-S cells. This behavior is consistent with the previous reports, e.g., nail penetration by Offer et al on Oxis’s MLP Li-S cells 4 and overcharge by Huang et al.5 More recently, thermal runaway tests performed on similar Oxis cells show the absence of runaway behavior during thermal ramp tests even up to 300oC, especially in cells with lean electrolyte. We are planning to perform a full suite of safety testing including ARC (Accelerated Rate Calorimetry) on larger prototype cells (4-5 Ah) to be fabricated on our pilot cell manufacturing line , which has recently been commissioned. In this paper, we will describe our recent results on Lyten Li-S cells both in performance and abuse testing.

References

Chen et al, "Toward Practical High-Energy-Density Lithium-Sulfur Pouch Cells: A Review", Adv. Mater. 2022, 2201555.

V. Mikhaylik and J. R. Akridge, “Polysulfide Shuttle Study in the Li-S Battery System”, J. Electrochem. Soc., 151, A1969-A1976 (2004).

Lyten patent on "Carbonaceous material for Li-S cells" US patent 11309 545 B2, April 19, 2022.

Hunt et al., J. Energy Storage, 2, 25 (2015).

Huang, et al., J.
Energy Storage Materials, 30, 87 (2020).

Figure 1