Impacts of Dissolved Ni²⁺ on the Solid Electrolyte Interphase on a Graphite Anode.

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium-ion battery (LIB) failure is often linked to transition metal ion dissolution from cathode materials.
• Nickel-rich layered cathodes are prone to Ni dissolution, impacting battery lifespan.
• Understanding Ni species distribution within the solid electrolyte interphase (SEI) is key to mitigating degradation.

Purpose of the Study:

• To investigate the impact and distribution of dissolved nickel (Ni) species on the SEI of graphite anodes in LIBs.
• To elucidate the mechanism by which Ni accumulation contributes to battery failure.
• To correlate Ni species presence with SEI properties and overall cell performance.

Main Methods:

• Utilized time-of-flight secondary ion mass spectroscopy (TOF-SIMS) for elemental and chemical analysis.
• Applied multivariate curve resolution (MCR) analysis to spatially map Ni distribution within the SEI.
• Employed accelerated aging protocols on LiNi_0.88 Co_0.08 Mn_0.04 O₂ /graphite full cells.

Main Results:

• Identified a multi-stratum structure within the SEI on graphite electrodes using EC-based electrolytes.
• Observed significant aggravation of Ni dissolution during accelerated aging upon cycling.
• Established a strong correlation between dissolved Ni and organic species within the SEI.
• Demonstrated Ni²⁺ and Li⁺ ion exchange as the primary cause of increased SEI resistivity.

Conclusions:

• Dissolved Ni species significantly impact the SEI structure and properties in LIBs.
• The ion-exchange reaction between Ni²⁺ and Li⁺ is a critical failure mechanism increasing SEI resistivity.
• Targeting Ni dissolution and SEI modification is crucial for enhancing LIB stability and longevity.