Experimental investigation of the thermal and cycling behavior of a lithium titanate-based lithium-ion pouch cell

Lithium-ion pouch cells with lithium titanate (Li4Ti5O12, LTO) anode and lithium nickel cobalt aluminum oxide (LiNi0.8Co0.15Al0.05O2, NCA) cathode were investigated experimentally with respect to their electrical (0.1C... 4C), thermal (5 degrees C ... 50 degrees C) and long-time cycling behavior. The 16 Ah cell exhibits an asymmetric charge/discharge behavior which leads to a strong capacity-rate effect, as well as a significantly temperature-dependent capacity (0.37 Ah . K-1) which expresses as additional high-temperature feature in the differential voltage plot. The cell was cycled for 10,000 cycles inbetween the nominal voltage limits (1.7-2.7 V) with a symmetric 4C constant-current charge/discharge protocol, corresponding to approx. 3400 equivalent full cycles. A small (0.192 m Omega/1000 cycles) but continuous increase of internal resistance was observed. Using electrochemical impedance spectroscopy (EIS), this could be identified to be caused by the NCA cathode, while the LTO anode showed only minor changes during cycling. The temperature-corrected capacity during 4C cycling exhibited a decrease of 1.28%/1000 cycles. The 1C discharge capacity faded by only 4.0% for CC discharge and 2.3% for CCCV discharge after 10,000 cycles. The cell thus exhibits very good internal-resistance stability and excellent capacity retention even under harsh (4C continuous) cycling, demonstrating the excellent stability of LTO as anode material. (C) 2018 Elsevier Ltd. All rights reserved.