Over the last decade, portable electronics and electric vehicle manufacturers have demanded Li-ion batteries with increasing energy density and lower costs, to satisfy the goals of smaller devices and greater run time, respectively. Other applications require Li-ion batteries with increased priority on cycle and calendar-life. These include vehicle-to-grid storage, stationary energy storage and battery leasing. Furthermore, increasing battery demand and limited production capabilities will create increased value for cells that can operate for longer without replacement by a new battery.
Li[Ni0.5Mn0.3CoO.2]O2//graphite (NMC532) pouch cells with only sufficient graphite for operation to 3.80 V (rather than ≥ 4.2 V) are presented as a low-voltage cell type for applications that require massive cycle and calendar-life. Cycling, ultra-high precision coulometry and impedance spectroscopy are used to characterize these cells and form a comparison with LiFePO4//graphite (LFP) pouch cells. LFP cells are often selected for applications that required good lifetime capabilities, but not the highest energy density. The low-voltage NMC532 cells are shown to be superior in both capacity retention and energy density to the LFP cells. Electrolyte chemistries and operating temperature and charging rate are explored to determine the impact on cycle-life. Lifetime predictions are made as a function of temperature and charging voltage, with room temperature operation beyond 100 years suggested in certain cases. In addition to incredible longevity, the nature of these cells poises them to be highly compatible with cutting-edge technologies such as high Ni, Co-free positive electrodes and fast charge liquid electrolytes. The potential long-term economic and performance advantage of this cell design warrant consideration by cell and device manufacturers.