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...

Lithium plating can be induced in any Li-ion cell that has a graphite negative electrode by increasing the charge rate sufficiently at fixed temperature or by lowering the temperature at a fixed charge rate. Recently, ethylene carbonate (EC)-free electrolytes, such as 1 M LiPF 6 in 98% ethyl methyl carbonate (EMC): 2% vinylene carbonate (VC), have been shown to passivate lithiated graphite effectively and allow Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 /graphite (NMC442/graphite) Li-ion cells to operate effectively for hundreds of charge discharge cycles. High charge rates and low temperatures were applied to Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC111/graphite) pouch cells containing EC-free EMC-based electrolytes with additives to study unwanted lithium plating. In such electrolytes, the plated lithium metal is not well passivated and reacts to create gas while in the same cells with 1 M LiPF 6 EC:EMC (3:7) electrolyte no gas is observed when Li plating occurs because EC passivates metallic Li well. The volume of the pouch cells with EC-free electrolytes increased sharply when Li plating occurred as measured using in-situ methods. In cells having both EC-based and EC-free electrolytes, lithium plating was the cause of rapid capacity loss at high charge rates at both 10 • C and 22 • Unwanted lithium plating in lithium ion batteries with graphite negative electrodes can be a serious aging mechanism. Unwanted lithium plating is most likely at low temperatures and high charge rates.1-3 The deposited Li metal can react with electrolyte, consuming active lithium and electrolyte, thus resulting in fast capacity fade. Unwanted lithium plating can be caused by increased resistance of the solid electrolyte interphase (SEI), 4 sluggish charge transfer kinetics, 5 insufficient ionic transport to the back of the graphite electrode and limited solid state diffusion, 6,7 among others. All of these increase cell polarization and drive the lithiated graphite to or below the potential of metallic Li. Therefore, the propensity toward unwanted Li plating in LIBs has a close relationship not only with the charging conditions such as low temperature, 8,9 high charging rates 10 and overcharging, 11,12 but also with the anode/cathode ratio, 13,14 carbonaceous materials selected 15,16 and the electrolyte used. 16,17The effect of different electrolyte systems on unwanted lithium plating behavior has been reported in several works. Smart and Ratnakumar showed that cells with high EC-content and SEI-stabilizing additives (like VC) were relatively prone to unwanted lithium plating probably due to the high-resistance SEI formed by VC.17 Yariv et al. showed that fluoroethylene carbonate (FEC) as a co-solvent could improve the low-temperature behavior of the lithiated graphite electrode and reduce the propensity for lithium plating. 16During recent years, electrolyte systems that are suitable for higher-voltage operation have been widely studied in order to improve the energy density of lithium-ion batteries. High-voltage NMC/ graphite cells can...