Mathematical Modeling of the Lithium Deposition Overcharge Reaction in Lithium‐Ion Batteries Using Carbon‐Based Negative Electrodes

485

434

Increasing the areal capacity or electrode thickness in lithium ion batteries is one possible means to increase pack level energy density while simultaneously lowering cost. The physics that limit use of high areal capacity as a function of battery power to energy ratio are poorly understood and thus most currently produced automotive lithium ion cells utilize modest loadings to ensure long life over the vehicle battery operation. Here we show electrolyte transport limits the utilization of the positive electrode at critical C-rates during discharge; whereas, a combination of electrolyte transport and polarization lead to lithium plating in the graphite electrode during charge. Experimental measurements are compared with theoretical predictions based on concentrated solution and porous electrode theories. An analytical expression is derived to provide design criteria for long lived operation based on the physical properties of the electrode and electrolyte. Finally, a guideline is proposed that graphite cells should avoid charge current densities near or above 4 mA/cm 2 unless additional precautions have been made to avoid deleterious side reaction. Lithium-ion (Li-ion) batteries are currently being used as the primary energy storage device in hybrid, plug-in, and all electric vehicles. This commercialization has been possible only by leveraging decades of previous scientific and engineering advances on materials, electrodes, and cell development. However, interactions in this complex system are still not fully understood. Automotive grade battery cells are required to fulfill a variety of optimization criteria in order to meet customer expectations and enable highly functional, robust and competitive products. In Fig. 1, key cell level criteria are shown for available technology as well as future development goals. Many of these values are highly influential on each other. In order to optimize one of the criteria it is always necessary to critically evaluate the impact on others. Key goals are to increase vehicle range and decrease cost at the same time. Minimizing the fraction of non-active material is an intuitive path to achieve these goals; however, the cell power and rate capability must simultaneously be maintained. [1][2][3] To derive clear development goals, the high level targets can be broken down to specific component requirements on the different levels of a storage system. 1,4 In Fig. 2, an analysis is shown for a state of the art prismatic hard-case automotive cell format. A battery level specific energy of ∼225 Wh/kg is widely accepted to be a critical value for sustainable implementation of long range electric vehicles. It represents a useful ratio between vehicle weight and range. In order to achieve this high specific energy, all subcomponents of the storage system have to meet demanding requirements as well. On the cell level, large format cells are favorable as they reduce the amount of cell housing needed per cell volume. Prismatic cell formats have a positive influence on the packing densi...

mentioning

confidence: 99%

Optimizing Areal Capacities through Understanding the Limitations of Lithium-Ion Electrodes

Gallagher

Trask

Bauer

et al. 2015

485

434

“…For example, a pseudo-two dimensional (P2D) model based on porous electrode theory has been applied to study the inhomogeneous degradation in the thickness direction. 7,22 In the P2D model, the gradients of the variables are assumed to be negligible in the other two directions, which are parallel to the current collectors. This assumption may be valid for small-scale cells, but is not reasonable for large-format cells.…”

mentioning

confidence: 99%

Simulation and Analysis of Inhomogeneous Degradation in Large Format LiMn₂O₄/Carbon Cells

Dai

Cai

White

2014

Self Cite

Degradation phenomena are not distributed uniformly in a large-format cell. To better understand the inhomogeneous degradation in large-format cells, a two-dimensional model was developed for a LiMn2O4 (LMO)/Carbon cell. The model includes both the non-uniform porous electrode properties and the electrode mismatch. The simulation results show that when the anode edge is extended over the cathode edge, the LMO particles near the edge suffer larger potential difference, larger charge/discharge depth, and higher insertion-induced stress. Therefore, the predicted loss of LMO is more pronounced near the edge as has been seen experimentally. The influence of different design adjustable parameters (such as: the anode extension length, the capacity ratio, the porosity, and the electrode thickness) and electrolyte properties (such as: the diffusion coefficient and the ionic conductivity) on the cathode performance. Among them, the over-potential behavior of the cathode is most sensitive to the extent of the electrode mismatch. Larger anode extensions will increase the possibility of the LMO degradation at the cathode edge. This suggests that a longer extension of the anode is not better for improvement of cell life. An optimal design of the anode extension length should be carried out.

“…[14][15][16][17][18] These electrochemical models tend to be computationally expensive, which has prohibited their use in the control and monitoring of internal states in real time. Several simplified/reduced electrochemical models have been proposed and control-relevant studies performed to try to address these issues.…”

Section: Model Descriptionmentioning

confidence: 99%

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

Suthar

Northrop

Braatz

et al. 2014

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. Lithium-ion chemistries are attractive for many applications due to high cell voltage, high volumetric and gravimetric energy density (100 Wh/kg), high power density (300 W/kg), good temperature range, low memory effect, and relatively long battery life.1-3 Capacity fade, underutilization, and thermal runaway are the main issues that need to be addressed in order to use a lithium-ion battery efficiently and safely over a long life.In order to address the aforementioned issues and increase battery utilization, smarter battery management systems are required which can exploit the dynamics of a battery to derive better operational strategies. Recognizing the potential of reducing the weight and volume of these batteries by 20-25% for vehicular applications, the Department of Energy has recently initiated a $30M program through ARPA-E named Advanced Management and Protection of Energy Storage Devices (AMPED). 4 The use of physically meaningful models in deriving these strategies has received attention. Methekar et al. 5 looked at the problem of energy maximization for a set time with constraints on voltage using Control Vector Parametrization (CVP). Klein et al. 6 considered the minimum-time charging problem while including constraints on temperature rise and side reactions. Rahimian et al. 7 calculated the optimal charging current as a function of cycle number for a lithium-ion battery experiencing capacity fade using a single-particle model (SPM). Hoke et al.9 used a lithium-ion battery life-time model to reduce battery degradation in a variable electricity cost environment using the SPM. Previous efforts included the derivation of optimal charging profiles considering various phenomena that account for capacity fade separately (plating over-potential at the anode, 13 side reaction during charging, 6 thermal degradation, 10 intercalation-induced stress using SPM 11 etc.). Fracture of solid electrode particles due to intercalation induced stresses is one of the dominant capacity fade mechanics which affect the battery capacity in two ways: 12 (1) It leads to loss of solid phase due to isolation from the electronically conducting matrix of electrode. (2) It also increases the surface area, which lead to SEI * Electrochemical Society Student Member.* * Electrochemical Soci...