Optimal Battery Operations and Design Considering Capacity Fade Mechanisms

Safely and capacity fade are the key issues that restrict the use of the lithium-ion battery for many applications. These issues are being tackled in a variety of ways. This dissertation focuses on using detailed continuum-level electrochemical models to study transport, kinetics, and mechanical processes in the lithium-ion batteries. These models can be used to quantify the effect of capacity fade mechanisms (side reactions and mechanical degradation) and improve the safety aspects of the lithium ion batteries. Three capacity-fade mechanisms—solid electrolyte interface side reaction, lithium-plating side reaction and mechanical degradation due to intercalation-induced stresses—are considered in the dissertation. Monitoring and control of plating side reaction is also very critical for battery safety. Two main focus areas of the dissertation are: 1) Optimal battery operation (design of charging/discharging protocols) considering three capacity fade mechanisms mentioned previously along with safety issues 2) Rational battery design (choice of porosity, thicknesses of electrodes, etc.) considering discharge capacity and capacity fade mechanism

Optimal charge/discharge profiles of mechanically constrained lithium-ion batteries

The cost and safety related issues of lithium-ion batteries require proactive charge and discharge profiles that can efficiently utilize the battery. Detailed electrochemical engineering based models that incorporate all of the key physics affecting the internal states of a lithium-ion battery are modeled using a system of coupled nonlinear partial differential equations. Careful choice of numerical discretization schemes and mathematical reformulation approaches can reduce the computational cost of these models to implement them in control relevant applications. The progress made in understanding the capacity fade mechanisms has paved the way for inclusion of that knowledge in deriving optimal charging/discharging profiles. Derivation of optimal charging/discharging profiles using physics based models enable us to provide constraints that can minimize local nonideal behavior and maximize efficiency locally and globally. This presentation will discuss derivation of optimal charging/discharging profiles which restrict various driving forces that accelerate capacity fade in a battery (e.g., temperature rise, over-potential for parasitic side reactions, intercalation induced stresses in solid phase) with minimal compromise on the amount of charge stored

Optimal Charging Profiles with Minimal Intercalation-Induced Stresses for Lithium-Ion Batteries Using Reformulated Pseudo 2-Dimensional Models

This paper illustrates the application of dynamic optimization in obtaining the optimal current profile for charging a lithium-ion battery by restricting the intercalation-induced stresses to a pre-determined limit estimated using a pseudo 2-dimensional (P2D) model. This paper focuses on the problem of maximizing the charge stored in a given time while restricting capacity fade due to intercalation-induced stresses. Conventional charging profiles for lithium-ion batteries (e.g., constant current followed by constant voltage or CC-CV) are not derived by considering capacity fade mechanisms, which are not only inefficient in terms of life-time usage of the batteries but are also slower by not taking into account the changing dynamics of the system.United States. Advanced Research Projects Agency-Energy (Award DE-AR0000275)Washington University (Saint Louis, Mo.

Modeling of a Lithium-Ion Battery-Photovoltaic Solar Cell Hybrid System

Many renewable forms of energy (ie. wind, solar, etc.) are intermittent in nature, which causes major problems when attempting to implement these types of energy into the electric grid [1]. Consumers demand an uninterrupted supply of power which requires constant generation sources. Although the amount of sunlight available in a given area is unpredictable, we can level the generation of an intermittent energy supply by coupling generation devices with energy storage systems (see Figure 1). At times of peak generation, part of the energy obtained can be transferred to a storage device, where it can be released during periods of low or no generation. This storage and release pattern can level the amount of renewable energy to provide a continuous source of power. Our study specifically investigates the coupled system of a p-n homojunction silicon solar cell and a Liion battery (see Figure 2). We model the combined system to study the effects on the system parameters and operating conditions caused by the coupling of the two systems. A electrochemical and transport based lithium ion battery model [2-5] and a 1-D continuum model of a p-n homojunction silicon solar cell [6-7] were validated independently and then coupled to use synchronized current and voltage conditions throughout the combined circuit. This hybrid system is then solved as a single, simultaneous system to obtain battery and cell characteristics through charging (generation) and discharging (no generation) cycles. The combined system will study the ability of the Li-ion battery to function efficiently as an energy storage device for solar generation. By solving both systems connected in circuit simultaneously we can study the effects each system has on each other dynamically. A simple circuit is considered which connects the battery and solar cell without any external voltage or current regulators. The voltage and current throughout the system are determined through the combined properties of the battery and solar cell. By obtaining results for a small hybrid system, we can better understand how the individual systems work in tandem and affect each other’s conditions. Future work will include optimizing the hybrid structure at the systems level as well as studying large scale systems that could be used for an entire solar farm