Aging‐Optimized Fast Charging of Lithium Ion Cells Based on Three‐Electrode Cell Measurements

Abstract

The widespread adoption of battery electric vehicles (BEVs) is thought to be hindered mainly by the achievable driving range, the cost, and the lifetime of the batteries. In addition, longdistance travel with BEVs is commonly viewed as cumbersome and time consuming due to long recharging times. Many BEVs recently introduced by various manufacturers solve the problem of driving range with big battery packs with more than 70 kWh of energy capacity. This also allows higher absolute charging power as the relative load for each battery cell remains small. Thus, a big car with a big battery can "recharge" more driving range per hour than a small car with a small battery. However, such big batteries are expensive, heavy, and not viable for smaller car models. To enable battery electric longdistance travel with minimal time penalty and maximum flexibility for drivers of small inexpensive electric car models, the batteries need to be able to recharge as quickly as possible. This would also allow people to own electric vehicles who do not have a personal parking space with their own charging port. Current electric vehicles mainly use lithium ion cell technology due to their high energy and power densities and potentially long lifetimes. [1,2] However, even the best state-of-the-art lithium ion cells suffer from various degradation mechanisms which limit their useful lifetime. [3] Parasitic side reactions of active materials and electrolyte components in the cell cause loss of usable cell capacity due to loss of mobile lithium ions and increasing internal resistance even if the cell is not used. [4] When a lithium ion cell is charged and discharged, different additional mechanisms damage the cell. Volume change of the anode and cathode active materials can cause particle cracking and thereby create fresh surface area which needs to be passivated. Moreover, it can lead to complete loss of electrical contact of active material particles to the current collector tabs. [3] Especially when charging a lithium ion cell, an additional and severely damaging effect can occur. If charging currents are too high or temperatures are too low, the intercalation of lithium ions into the anode active material can become too slow and lithium metal is deposited on the surface of the anode particles, so-called lithium plating. [3,5-8] Bare lithium metal will readily react with the electrolyte to form new passivating films that bind lithium ions irreversibly and increase the internal resistance of the cell. [7-9] This is known to drastically increase the aging rate and loss of usable capacity of a lithium ion cell. [8,9] It is also possible that lithium metal dendrites grow through the separator and create shorts in the cell, which can increase the self-discharge of the cell or even lead to thermal runaway. [5] Finding the best fast charging protocol for a given battery has been the focus of various publications. [10-20] The aim is to have a minimal charging time without increased aging or at least an

How Fast Can a Li-Ion Battery Be Charged? Determination of Limiting Fast Charging Conditions

“…Three-electrode cells can directly monitor electrode potentials in operando and have been used to inform the development of charging protocols that can avoid Li plating. − The main limitation of such experiments is that they only approximate the true potentials experienced by the electrodes, especially at high charging currents . Electrode potentials are formally defined as the difference in electrical potential between the solid matrix and the electrolyte at a certain depth of the electrode; as such, it is characterized by a range of values at a given time, rather than a single potential. , Furthermore, design constraints require the reference probe to be placed at a finite distance away from the cathode and the anode, causing the sensed values of electrolyte potential to differ from that experienced at the working electrode .…”

An Experimental Method to Determine the Measurement Error of Reference Electrodes within Lithium‐Ion Batteries

“…Previous studies have shown how the anode potential can be used to perform charging protocols. [24][25][26][27][28][29] In contrast to a regular constant current constant voltage (CCCV) protocol, the CV phase is not adjusted to the cell voltage but to the reference potential (CV ref ). During the CC phase, a high C-rate can be applied until a fixed cut-off reference potential is reached.…”

Online Fast Charging Model without Lithium Plating for Long-Dimensional Cells in Automotive Applications

“…The cell's negative electrode potential is monitored at various charge rates to prevent it from dropping below 0 V (vs Li/Li + ). Below this potential, lithium ions will preferentially gain electrons on the negative electrode surface and form a lithium plate [22,23,38]. Currently, the electroplating of a lithium metal layer on a copper wire surface is the most widely used and mature reference electrode preparation process for LIBs.…”

“…There are also fast-charging strategies that rely on cell feedback and model simulations. Considering the relationship between lithium plating and the negative electrode potential of the cell, one approach involves implanting a reference electrode in the cell to measure the negative electrode potential and achieve fast charging without lithium plating by controlling this potential [22][23][24]. However, it is not feasible for real cells to constantly carry reference electrodes for negative electrode potential measurements in practical scenarios.…”