Rate capability refers to a battery’s ability to maintain its capacity and efficiency when charged or discharged at different rates. It’s often examined by seeing how much capacity a cell delivers at 1C, 2C, 5C, etc., compared to its capacity at a low rate (like C/10). A battery with excellent rate performance might still provide near its full capacity even at 2C or 5C discharge, whereas one with poor rate performance could see a significant drop in capacity at those higher currents. Rate performance is limited by kinetic factors: if lithium ions can’t move quickly enough through the, the battery can’t utilize all its active material at fast rates, leading to what’s called “rate capability” limitations. Good rate performance is crucial for high-power applications and fast charging.
NOVONIX routinely assesses rate performance in its testing routines.They run a rate map, or series of discharges: e.g., discharge at C/20 (very slow, near theoretical capacity), then at C/5, 1C, 2C, 5C, etc., recharging at CC/CVbetween discharges. This yields a curve or set of data points showing capacity vs rate. They similarly test charge rate performance, discharging fully between charges. NOVONIX analyzes the mechanisms causing the drop in capacity at higher rates and suggest potential strategies to improve rate performance. NOVONIX also uses rate performance tests to compare materials: if a new cathode material shows 80% capacity at 5C vs the baseline’s 70%, that’s a win for rate capability for the new cathode material. Additionally, these tests can inform thermal management needs, as high rates generate heat. Overall, by thoroughly characterizing and improving rate performance, NOVONIX helps ensure that batteries can meet the power delivery and fast-charge demands of modern applications.
