6K INC. — Department of Defense SBIR Phase I: DLA203-004

Description

The nickel content of oxide-based lithium-ion cathodes has trended steadily upward to enable higher energy density in both portable power and automotive applications. However, stability and reactivity issues have slowed the adoption of NMC 811 in the market. This is because high Ni cathode materials suffer from multiple failure modes caused by the high Ni content itself: 1) bulk destabilization of the structure in the charged state where oxygen is oxidized and lost, leaving Ni2+ which migrates from the transition layer into the lithium layer; 2) a change in nickel oxidation state  at the grain boundaries where the ordered, layered structure converts to spinel and then NiO, increasing impedance and promoting intragranular cracking; and 3) electrolyte instability at the surface, where Ni4+ and Ni2+ oxides serve as catalytic surfaces causing gassing and other decomposition pathways for the electrolyte solvent.    Single-crystal cathode materials have demonstrated benefits in cycle life, reactivity, and safety  through mechanisms that address the failure modes of high-nickel materials. Namely, single crystal materials have no intraparticle grain boundaries vulnerable to failure mode 2. Also, single crystal cathode grain surfaces have lower surface area and are relatively defect free compared to their polycrystalline counterparts, mitigating failure mode 3.  Thus, single crystal materials can enable 811 and higher nickel contents, because both modes 2 and 3 are reduced or eliminated.  Unfortunately, the same factors causing performance challenges in high Ni materials also make the production of single crystal materials challenging and expensive, requiring multiple additional process steps when made by conventional methods.   6K’s patented UniMelt® microwave plasma materials production technology represents a solution to these challenges.  The UniMelt® process is high throughput, scalable, sustainable, and offers a significant cost advantage over the conventional coprecipitation method, particularly for single crystal materials. 6K has performed early proof of concept work showing that single crystal high Ni NMC material can be produced using UniMelt®.  In phase 1 of this program, we propose to complete the feasibility demonstration, achieving full electrochemical performance and demonstrating single crystal NMC with Ni contents up to 0.9, laying the groundwork for a low cost domestic supply of advanced oxide cathode materials.