Lithium Plating: How Mathematics Can Help to Identify Fast-Charging Limits
Authors: Carelli Serena , Bessler Wolfgang G. 
Published: May 2020

With their growing importance in the market of electric vehicles and energy storage, a more comprehensive evaluation of Li-ion batteries behavior has become necessary for the power sources industry. Mathematical modelling and numerical simulation have become standard techniques in Li-ion battery research and development, with the purpose of studying the issues of batteries, including performance and ageing, and consequently increasing the predictability of model-based life expectancy. The efficient and fast charging of Li-ion batteries remains at the moment one of the most delicate challenges for the automotive and energy industries, being seriously affected by the formation of lithium metal on the surface of the anode during charge. This degradation process is called lithium plating and happens to be very damaging for the mechanical and chemical integrity of the battery, which not only sees its capacity lowered but could also incur serious damage and the risk of explosion. It is very difficult to detect lithium plating in situ without a direct observation of the open cell, but it is possible to deduce its presence by analyzing the cell behavior during cycles of charge/discharge in critical conditions and detecting some peculiarities which have been shown to indicate plating. The most common hints are a voltage plateau due to lithium oxidation during discharge at constant temperature and a voltage drop due to re-intercalation of metallic lithium during heating of the cell. On the other hand, the absence of any evidence of changes in voltage should not be considered as proof of evidence of a complete absence of lithium plating.

Following our development of a comprehensive modelling and simulation framework for a commercial 0.35 Ah high-power lithium-ion pouch cell with LCO/NCA blend cathode1, here we present an extended pseudo-3D (P3D) model in which a lithium plating reaction has been integrated and parameterized. An extended bibliographic research helped us in choosing suitable parameters for modelling the plating kinetics. The model is now able to describe and predict both the equilibrium potentials and the non-equilibrium kinetics of the competing intercalation and plating reactions for arbitrary macroscopic operating conditions (C-rate, temperature, SOC). A relatively simple and common way to assess plating risk with P2D models is to compare the simulated local anode potential ΔΦ
an with the thermodynamic plating condition of ΔΦ
Li
eq = 0 V, but this approach shows several pitfalls that have not been well discussed in literature. These issues have been included and discussed in detail in the present model, which has carefully been built to consider the effects of temperature, pressure and ion concentration on the thermodynamics and kinetics of the plating reaction. Consequently, this model also allows the creation of operation maps and an accurate spatiotemporal analysis of the competing reactions and lithium plating formation at the electrode-pair scale (1D, mesoscale) and intraparticle scale (1D, microscale) over a wide range of conditions. The governing equations for this model are implemented in the in-house multiphysics software package DENIS. The electrochemistry model is based on the use of the open-source chemical kinetics code CANTERA, enabling the thermodynamically consistent description of the main and side reactions, which is coupled to the DENIS transport model via the chemistry source terms.

To validate our extended model, we also simulated and successfully reproduced the experimental data from Ecker et al. 2 for 1C charge-discharge at different temperatures. The unavoidable differences are due to the different size and characteristics of Ecker’s battery, measured experimentally (40 Ah high-power lithium-ion pouch cell with NMC cathode) and our virtual battery (0.35 Ah high-power lithium-ion pouch cell with LCO/NCA blend cathode).

References

1. S. Carelli, M. Quarti, M. C. Yagci and W. G. Bessler, J. Electrochem. Soc.,
166(13), A2990-A3003 (2019).

2. M. Ecker, Lithium Plating in Lithium-Ion batteries: An experimental and simulation approach, PhD Thesis, RWTH Aachen University (2016).

Figure 1