Effects of Electrolyte Additives and Solvents on Unwanted Lithium Plating in Lithium-Ion Cells

Abstract

Unwanted lithium plating on the graphite anode of lithium ion batteries can reduce the cycle life and safety of lithium ion batteries. Increased charging rates, lower temperatures, thicker electrodes, lower Li-ion diffusion constant and larger graphite particles all increase the propensity for unwanted lithium plating. In this work, a variety of electrolyte additives and electrolytes, which extend lifetime during low rate cycling, were used in Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC111/graphite) pouch cells subjected to high rate charging at 20 • C. It was found that additives and electrolytes which increased the negative electrode area-specific resistance, R negative , decreased the onset current, I u , for unwanted lithium plating. Here, the processes of ion desolvation, electron and ion transport through the solid electrolyte interphase and contact resistance are lumped into the R negative . Under conditions where R negative is the dominant factor determining when unwanted Li plating occurs, the onset current for lithium plating could be well predicted by the expression: I u = 0.080 V x S/R negative , where S is the geometric electrode surface area. R negative is easily determined using negative electrode coin-type symmetric cells. This simple rule-of-thumb relation will help guide researchers seeking to select electrolyte additives that simultaneously increase lifetime and also allow fast charging. Unwanted lithium plating can occur in Li-ion cells at high charge rates due to the close working potential of the graphite anode to metallic lithium. If the lithium ions and corresponding electrons cannot intercalate within the graphite particles fast enough, then metallic lithium can deposit on the surface of the graphite anode. Unwanted lithium plating is one mechanism that can limit the lifetime of lithiumion cells. Even worse, plated Li can form dendrites which may pierce the separator and affect the safety of lithium-ion cells. 1,2The propensity for unwanted lithium plating depends on many factors such as electrolyte components, 3 cell design (e.g., anode/cathode ratios, thickness and porosity of the graphite anode), 4 cell history and age (e.g., thickening of the negative electrode solid electrolyte interphase (SEI)) 5 and harsh charging conditions (e.g., high charge rates, low temperature and overcharge).6-8 Among these factors, the electrolyte used in lithium-ion cells not only determines the ionic conductivity but also plays a significant role in determining the properties of the SEI films.9,10 Therefore, the electrolyte components (i.e., Li salt, solvents and additives) can strongly affect unwanted lithium plating.The choice of appropriate electrolyte additives is an efficient and simple way to improve the lifetime of Li ion batteries by modifying the SEI properties.11 Vinylene carbonate (VC) has been commonly used as an additive for forming a robust negative electrode SEI and has been shown to improve the cycle life and calendar life of Li-ion cells.12-14 Ethylene sulfite (ES) was reported to form a...

Development of Electrolytes for Single Crystal NMC532/Artificial Graphite Cells with Long Lifetime

“…Figure 3 shows that cells with PES as the primary additive exhibited large capacity losses of ∼50-90 mAh after testing with 1 C charging for 30 cycles, which is primarily due to unwanted lithium plating. 23 Cells with FEC or VC or/and DTD showed negligible capacity loss during the 1 C charging test, indicating the absence of unwanted lithium plating. This result agrees well with Figure 1a which shows that cells with PES showed significantly higher R ct than cells with FEC or VC.…”

“…Liu et al showed that NMC111/graphite cells with PES211 electrolyte could not be charged at a C/2 rate at room temperature without unwanted lithium plating (detailed electrode information can be found in Reference 23). 23 If single crystal NMC532 * Electrochemical Society Student Member. * * Electrochemical Society Fellow.…”

“…23 Such additives are often those that also increase lifetime of cells under moderate rate conditions. PES211 electrolyte usually leads to large negative electrode charge transfer resistance and therefore is not suitable for applications requiring high rates during charging.…”

“…Liu et al showed that NMC111/graphite cells with PES211 electrolyte could not be charged at a C/2 rate at room temperature without unwanted lithium plating (detailed electrode information can be found in Reference 23). 23 If single crystal NMC532 materials are commonly used, charging at C rate is desired. Hence, this work will focus on the development of alternative electrolyte additives for single crystal NMC532/graphite cells that can support long lifetime as well as C-rate charging at both room and elevated temperatures.…”

Electrochemical, Post-Mortem, and ARC Analysis of Li-Ion Cell Safety in Second-Life Applications

“…[16][17][18][19] Operating conditions and materials have a strong influence on these aging mechanisms. 12,[20][21][22][23] We recently reported on a change of the aging mechanism with temperature for cycling aging of commercial 18650-type cells with graphite anodes and NMC/LMO cathodes. 20 This mechanism change is expressed by a V-shape in Arrhenius plots of the capacity fade rates obtained from cycling at different ambient temperatures.…”