[Paper Review] Simultaneous Single Crystal Growth and Segregation of Ni-Rich Cathode Enabled by Nanoscale Phase Separation for Advanced Lithium-Ion Batteries

Yujing Bi, Yaobin Xu+16 more|arXiv (Cornell University)|Jun 20, 2023

Advancements in Battery Materials4 citations

TL;DR

This study presents a novel molten-salt-free synthesis route for high-performance single-crystal NMC811 cathodes by leveraging nanoscale phase separation during precursor processing. By controlling the morphology of Ni-Co-Mn hydroxide precursors, the method enables simultaneous single-crystal growth and Ni segregation via concurrent formation of spinel and rock salt phases in transition metal oxide intermediates, yielding 1000-cycle stable 2Ah pouch cells with enhanced structural integrity.

ABSTRACT

Synthesis of high-performance single crystal LiNi0.8Mn0.1Co0.1O2 (NMC811) in the absence of molten salt is challenging with no success yet. An innovative drop-in approach is discovered to synthesize single crystal NMC811 by controlling the morphology of transition metal hydroxide TM(OH)2 precursors followed by a simple decomposition step to form transition metal oxide (TMO) intermediates. Ni redistribution in TMO, as a result of the concurrent formation of mixed spinel and rock salt phases, helps deagglomerate the later formed NMC811 clusters of single crystals. As-prepared single crystal NMC811 is validated in a 2Ah pouch cell demonstrating 1000 stable cycling. The fundamentally new reaction mechanism of single crystal growth and segregation without molten salt provides a new direction towards cost-efficient manufacturing of single crystal NMC811 cathode for advanced lithium-based batteries.

Motivation & Objective

• To develop a cost-effective, molten-salt-free synthesis route for single-crystal Ni-rich NMC811 cathodes.
• To overcome the challenge of agglomeration during single-crystal formation in conventional solid-state synthesis.
• To enable simultaneous single-crystal growth and Ni segregation through controlled phase separation in oxide intermediates.
• To achieve high cycling stability and structural robustness in full-cell configurations.
• To establish a scalable, industrially viable pathway for advanced lithium-ion battery cathodes.

Proposed method

• Controlled synthesis of Ni-Co-Mn hydroxide (TM(OH)2) precursors with tailored morphology to guide subsequent phase evolution.
• Thermal decomposition of precursors to form mixed transition metal oxide (TMO) intermediates with coexisting spinel and rock salt phases.
• Nanoscale phase separation during TMO formation induces Ni redistribution, preventing particle agglomeration.
• Subsequent lithiation and crystallization yield single-crystal NMC811 with homogeneous Ni distribution and reduced intergranular strain.
• Use of a simple, scalable solid-state reaction without molten salt fluxes.
• Validation of the synthesized cathode in a 2Ah pouch cell under standard cycling protocols.

Experimental results

Research questions

• RQ1 Can single-crystal NMC811 be synthesized without molten salt fluxes through controlled phase separation?
• RQ2 How does nanoscale phase separation in TMO intermediates influence Ni distribution and crystal growth?
• RQ3 What is the role of spinel and rock salt phases in deagglomeration during single-crystal formation?
• RQ4 Can the resulting single-crystal NMC811 achieve long-term cycling stability in full-cell configurations?
• RQ5 Is the proposed method scalable and suitable for industrial production of high-nickel cathodes?

Key findings

• The method successfully produces single-crystal NMC811 without molten salt, overcoming a long-standing synthesis challenge.
• Nanoscale phase separation in TMO intermediates enables concurrent single-crystal growth and Ni segregation, reducing agglomeration.
• The presence of mixed spinel and rock salt phases in TMO facilitates Ni redistribution and promotes single-crystal formation.
• The as-prepared NMC811 cathode delivers 1000 stable cycles in a 2Ah pouch cell with high capacity retention.
• The absence of molten salt simplifies processing and improves cost-efficiency for industrial-scale production.
• The reaction mechanism reveals a fundamentally new pathway for single-crystal cathode synthesis with enhanced structural stability.