Advanced High-nickel Layered Oxide Cathodes for Lithium-ion Batteries

Download or read book Advanced High-nickel Layered Oxide Cathodes for Lithium-ion Batteries written by Wangda Li and published by . This book was released on 2018 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: The growing demand for rechargeable Li-ion batteries with higher performance metrics has spurred intensive research efforts. In the quest for safe and low-cost cathode materials with desirable energy/power capabilities, high-nickel layered oxides (LiNi [subscript 1- x] M [subscript x] O2; x 0.5, M = Co, Mn, Al) are among the most promising candidates. However, limited cycle/calendar life especially at elevated temperatures and poor thermal-abuse tolerance are serious challenges for their practical applications. This dissertation focuses on the fundamental understanding of electrode-electrolyte incompatibility for high-Ni LiNi [subscript 1-x] M [subscript x] O2 with state-of-the-art nonaqueous electrolytes at deep charge during battery operation, and corresponding strategies for inhibiting the associated unwanted parasitic reactions and enabling excellent cyclability/safety in practical cell configurations. First, we reveal the dynamic behaviors of the CEI on LiNi [subscript 0.7] Co [subscript 0.15] Mn [subscript 0.15] O2 driven by conductive carbon in composite electrodes. Secondary-ion mass spectrometry (SIMS) shows that the CEI, initially formed on carbon black from spontaneous reactions with the electrolyte prior to cell operation, passivates the cathode through a mutual exchange of surface species. By tuning the CEI thickness, we demonstrate its impact on the evolution of the electrode-electrolyte interface during cell operation at high voltages. Next, we study the evolution of the SEI on anodes, where metallic Li deposition causes capacity fade and safety issues. On graphite harvested from pouch cells paired with LiNi [subscript 0.61] Co [subscript 0.12] Mn [subscript 0.27] O2 after 3,000 cycles, SIMS reveals large Li deposition in the SEI, triggered by transition-metal cations dissolved from the cathode and migrated to the anode. With Al doping (~1 mol %) in LiNi [subscript 0.61] Co [subscript 0.12] Mn [subscript 0.27] O2, dissolution is effectively inhibited and superior long-term cyclability is achieved ( 80% after 3,000 cycles). With knowledge on both electrodes, we then conduct a comprehensive assessment on the long-term cyclability of high-Ni LiNi [subscript 0.7] Co [subscript 0.15] Mn [subscript 0.15] O2 and commercially established LiNi [subscript 0.8] Co [subscript 0.15] Al [subscript 0.05] O2 in pouch full cells (1,500 cycles). Various degradation processes leading to performance deterioration are carefully invesitgaeted. Based on the results, we identify key challenges, relative to NCA, for realizing a long service life of high-Ni NCM and corresponding mitigation strategies. Finally, we design tailored nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC) and realize unusual thermal and electrochemical performance of an ultrahigh-nickel cathode (LiNi [subscript 0.94] Co [subscript 0.06] O2), reaching a specific capacity of 235 mA h g−1. By using two model electrolyte systems, we present assembled graphite|LiNi [subscript 0.94] Co [subscript 0.06] O2 pouch full cells with exceptional thermal stability, energy/power capabilities, and long service life