Ethylene Carbonate-Free Electrolytes for High-Nickel Layered Oxide Cathodes in Lithium-Ion Batteries

Layered lithium nickel oxide (LiNiO2) can provide very high energy density among intercalation cathode materials for lithium-ion batteries, but suffers from poor cycle life and thermal-abuse tolerance with large lithium utilization. In addition to stabilization of the active cathode material, a concurrent development of electrolyte systems of better compatibility is critical to overcome these limitations for practical applications. Here, with nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC), superior electrochemical and thermal characteristics are obtained with an ultrahigh-nickel cathode (LiNi0.94Co0.06O2), capable of reaching a 235 mA h g(-1) specific capacity. Pouch-type graphite|LiNi0.94Co0.06O2 cells in EC-free electrolytes withstand several hundred charge-discharge cycles with minor degradation at both ambient and elevated temperatures. In thermal-abuse tests, the cathode at full charge, while reacting aggressively with EC-based electrolytes below 200 degrees C, shows suppressed self-heating without EC. Through 3D chemical and structural analyses, the intriguing impact of EC is visualized in aggravating unwanted surface parasitic reactions and irreversible bulk structural degradation of the cathode at high voltages. These results provide important insights in designing high-energy electrodes for long-lasting and reliable lithium-ion batteries.