Voltage-based accelerated aging tests are critical for evaluating battery longevity and understanding degradation mechanisms under electrical stress. These tests focus on how voltage parameters influence battery aging, isolating electrical factors from other stressors like temperature. The primary voltage stress conditions include overcharge, over-discharge, float voltage, and varying state-of-charge (SOC) windows. Each condition accelerates distinct degradation pathways, including solid electrolyte interface (SEI) growth, cathode structural changes, and lithium plating.

Overcharge and over-discharge protocols involve pushing cells beyond their designed voltage limits. Overcharge tests typically apply voltages exceeding the upper cutoff, such as 4.5V for lithium-ion cells with a nominal 4.2V limit. This forces excessive lithium extraction from the cathode, causing oxygen release, transition metal dissolution, and electrolyte oxidation. Over-discharge tests drive cells below the lower voltage cutoff, such as 2.0V for a 3.0V minimum, leading to copper current collector dissolution and anode structural damage. IEEE 1188 specifies standardized overcharge/discharge protocols for lead-acid batteries, while DOE test manuals outline similar procedures for lithium-ion systems.

Float voltage stress tests maintain cells at a constant high voltage, often slightly below the upper cutoff, to simulate conditions like grid storage or backup power applications. For example, holding a lithium-ion cell at 4.1V instead of cycling it between 3.0V and 4.1V accelerates SEI growth due to sustained electrolyte reduction at the anode. Float voltage also promotes cathode electrolyte interphase (CEI) formation, increasing impedance and capacity fade. Industry data shows that float charging at 100% SOC can double the rate of capacity loss compared to 80% SOC storage.

SOC window impact studies compare degradation rates under different cycling ranges. Cycling between 20% and 80% SOC produces less degradation than 0% to 100% due to reduced mechanical strain on electrode materials and slower SEI growth. At high SOC (above 90%), the anode potential drops low enough to accelerate electrolyte reduction, thickening the SEI layer. Meanwhile, the cathode operates at high potentials where oxidative side reactions degrade the active material. Research indicates that cycling within a 50% to 80% SOC window can extend cycle life by over 300% compared to full-range cycling.

Voltage stress accelerates SEI growth through increased electrolyte reduction kinetics. At higher anode potentials (low cell voltages), the driving force for electrolyte decomposition rises, forming a thicker SEI that consumes active lithium and increases impedance. Cathode degradation under high voltage involves lattice instability, phase transitions, and transition metal dissolution. For example, layered oxides like NMC lose oxygen at voltages above 4.3V, while spinel cathodes like LMO undergo manganese dissolution. Lithium plating occurs when the anode potential drops below 0V vs. Li/Li+, causing metallic lithium deposition that reduces cyclable lithium and creates dendrite risks.

Anode-driven degradation dominates in high-SOC or over-discharge conditions where SEI growth and lithium plating are prevalent. Graphite anodes experience volume changes that crack the SEI, exposing fresh surfaces to further electrolyte reduction. Silicon-containing anodes suffer from severe particle fracturing due to their large expansion. Cathode-driven degradation prevails during overcharge or float voltage tests, where oxidative processes degrade the active material and electrolyte. NMC cathodes lose capacity through microcracking and cation mixing, while LFP exhibits slower degradation due to its stable olivine structure.

Industry standards provide frameworks for voltage-based aging tests. IEEE 1188 outlines float and cycle testing for lead-acid batteries, specifying voltage limits and capacity measurement intervals. DOE test manuals for lithium-ion batteries define protocols for overcharge tolerance, SOC window studies, and impedance tracking. These standards ensure comparable data across different labs and battery types.

Quantitative studies demonstrate voltage-dependent aging rates. For instance, NMC/graphite cells cycled between 3.0V and 4.1V retain 80% capacity after 1,000 cycles, while those cycled to 4.3V reach 80% in just 500 cycles. Similarly, LFP cells stored at 100% SOC lose 5% capacity per month, whereas those stored at 50% SOC lose less than 1%. These trends highlight the tradeoff between energy utilization and longevity.

In summary, voltage-based accelerated aging tests reveal critical insights into battery degradation mechanisms. Overcharge, over-discharge, float voltage, and SOC window studies each target specific failure modes, from SEI growth to lithium plating and cathode degradation. Anode-driven mechanisms prevail under low-voltage stress, while cathode-driven processes dominate at high voltages. Industry standards like IEEE 1188 and DOE manuals ensure consistent testing methodologies, enabling reliable predictions of battery lifespan under electrical stress conditions.