Mixed Modes Fracture and Fatigue Evaluation for Lithium-ion Batteries

Lithium ion batteries have become a widely known commodity for satisfying the world’s mobile energy storage needs. But these needs are becoming increasingly important, especially in the transportation industry, as concern for rising oil prices and environmental impact from fossil fuels are pushing for deployment of more electric vehicles (EV) or plug in hybrid-electric vehicles (PHEV) and renewable energy sources. The objective of this research is to obtain a fundamental understanding of degradation mechanisms and rate-capacity loss in lithium-ion batteries through fracture mechanics and fatigue analysis approaches. In this study we follow empirical observations that mechanical stresses accumulate on electrode materials during the cycling process. Crack induced fracturing will then follow in the material, degrading the electrical contact surface area and reducing the capacitance of the battery. A fatigue analysis simulation is applied using ANSYS finite element software coupled with analytical models to alleviate these parameters that play the most pivotal roles in affecting the rate-capacity and cycle life of the lithium-ion battery. Our results have potential to provide new models and simulation tools for clarifying the interplay of structure mechanics and electrochemistry while offering an increased understanding of fatigue degradation mechanisms in rechargeable battery materials. These models can aid manufacturers in the optimization of battery materials to ensure longer electrochemical cycling life with high-rate capacity for improved consumer electronics, electric vehicles, and many other military or space applications. ENERGY OUTLOOK For decades, petroleum products have been the backbone for transportation in the U.S. and around the world. About 50% of petroleum consumption is dedicated to the transportation industry while the other 50% is comprised for electricity generation and industrial or residential use [1]. Today’s society has become heavily reliant on oil consumption for its day-today activities, and prices are predicted to keep rising at relatively constant rates (Fig. 1). This over-reliance on petroleum will only stymie the world in the future as oil reservoirs are drained and fuel prices skyrocket. In addition, environmentalist and scientist alike have studied the negative effects of the enormous carbon emissions to our atmosphere. It has been reported that 98% of all carbon dioxide emissions, the main contributor, come from petroleum fuels [2]. This has induced the drive for ‘going green’ which has become a worldwide epidemic. Thus, need to reduce our carbon footprint, especially in the petroleum driven transportation sector, is changing the way we design for the future. Government policy has recently set requirements for auto manufactures by year 2016 in which an average of 35.5 mpg and a maximum CO2 exhaust level of 250 grams per mile must be achieved for ‘light vehicles’ [3]. Therefore researchers have increased efforts in looking for alternative fuels and energy sources such as improved batteries for hybrid and electric vehicle transportation in particular [4]. Figure 1: Current and future market trends in the oil industry for transportation, industrial use, residential and electricity generation. Trends show consistent increases in consumption and price through year 2035, but price increases at a slightly higher rate. *Corresponding author