Extreme Fast‐Charging of Lithium‐Ion Cells: Effect on Anode and Electrolyte

Abstract

's the nearest charging station?" may soon replace the more common question, "Where's the nearest gas(oline) station?" as electric vehicles become ubiquitous on roads and highways. Today's gasoline-powered automobiles can typically refuel in about 10 min or less. Performing the same task with a lithium-ion-battery-powered vehicle would require that the battery be recharged at about the 6-C rate or higher. At this high charge rate, lithium metal can plate at the negative electrode, introducing a potential safety issue. The effects of fast charging and of lithium plating on the performance of the graphite anode have been reported by Murkherjee and coworkers using 0.5-, 1-, and 1.5-C charging rates as well as subambient temperatures. [1,2] Here, the authors report that lithium plating is anode-centric and can be heterogenous. Some regions of the anode will display copious amounts of plating, whereas others show relatively little. They report that, once plating occurs, there was an increase in the resistance of the anode and massive porosity loss, resulting in rapid capacity decline due to underlithiation. Indeed, the charge rate and temperature affected the morphology of the lithium deposit. Murkherjee and coworkers modeled the lithium-plating process on a graphite anode to understand its complex behavior. [3] This physics-based model showed how heterogeneities in the electrode resulting in preferential plating. The result of the model showed that both the cathode and the anode interact nonlinearly to produce odd-looking lithium-plating deposits. Lithium plating is not the only undesired artifact of high-rate charging. In theory, there may be changes in the electrolyte caused by the rapid deposition of lithium and/or heating from the high current. These changes can alter the conductivity of the electrolyte, leading to performance and life degradation. Changes in the composition of the electrolyte have been studied extensively under normal operating conditions. [4-28] These studies ranged from characterizing electrolyte changes in small cells [4-10,12-28] to fieldtested, automotive-class batteries. [29] The effect of fast charging on cell components was reviewed recently by Ahmed et al. [30] However, there are no reports in the open literature regarding the changes in the electrolyte caused by fast charging. The reported changes in the electrolyte with typical charge rates were due to transesterification of the carbonates; [31] the reaction of LiPF 6 with residual water; [7,32] and the reduction of an organic carbonate, [30] such as ethylene carbonate (EC), and subsequent recombination with other organics and/or fragments of the PF 6 À anion. [4,25,32-35] Many reactions of the general nature shown in Scheme 1 were proposed as routes to obtain the observed species in the electrolyte and on the surface of the negative electrode. The ─OR and ─OR x (x ¼ 1, 2, or 3) groups in the last line of Scheme 1 are alkoxy fragments that may be produced in the decomposition reactions; they do not have to be the same.

A Comprehensive Understanding of the Aging Effects of Extreme Fast Charging on High Ni NMC Cathode

“…The R SEI and R B for the NMC811 cells, as summarized in Figure 2c and Figure 2e, closely follow the capacity fade trend observed in Figure 2a, commensurate to more SEI growth and electrolyte decomposition at the anode (see Figure S5 in the Supporting Information for additional explanation). [ 12,15,19,39,40 ] The NMC811 aging issues captured through the R CEI+CT impedance in Figure 2d, [ 41,42 ] as obtained from the mid‐frequency depressed semi‐circle in Figure S4 in the Supporting Information, show a gradual increase with cycling for 1C to 9C and 4.1 V charging conditions. This gradual and less severe increase in R CEI+CT in Figure 2d is starkly different from the NMC532 cells that showed sped up cathode degradation after about 400 cycles for the same fast‐charge cycling conditions, as shown in Figure 2 in ref.…”

Effect of Salt Concentration on the Interfacial Solvation Structure and Early Stage of Solid–Electrolyte Interphase Formation in Ca(BH4)2/THF for Ca Batteries

“…The Ca-deposited quartz electrodes were thoroughly rinsed with THF before being examined under the microscope. As described in an earlier work, 35 the electrode samples were placed in an airtight holder in the glovebox and transferred into the SEM chamber without air exposure. Images and EDS spectra were taken using a JEOL JSM-6610LV SEM coupled with EDS dectector (Oxford).…”

Quantitative Analysis of Origin of Lithium Inventory Loss and Interface Evolution over Extended Fast Charge Aging in Li Ion Batteries

“…The experimental procedures for ICP-OES can be referred to our previous publications. 4,14 5.3.1. NMR.…”