Effects of Biphenyl Polymerization on Lithium Deposition in Commercial Graphite/NMC Lithium-Ion Pouch-Cells during Calendar Aging at High Temperature

Abstract

Metallic lithium deposition is a typical aging mechanism observed in lithium-ion cells at low temperature and/or at high charge rate. Lithium dendrite growth not only leads to strong capacity fading, it also causes safety concerns such as short-circuits in the cell. In applications such as electric vehicles, the use of lithium-ion batteries combines discharging, long rest time and charging phases. It is foremost a matter of lifetime and safety from the perspective of the consumer or the investor. This study presents the post-mortem analyses of commercial 16 Ah Graphite/NMC (Nickel Manganese Cobalt layered oxide) Li-ion pouch cells. The cells were degraded by calendar aging at high temperature with or without periodic capacity tests. Unexpected local depositions of metallic lithium were confirmed on graphite electrodes by Nuclear Magnetic Resonance (NMR). Biphenyl, a monomer additive present in the liquid electrolyte, generates gas during its polymerization reaction occurring at high temperature and at high state of charge. As a result, dry-out areas are present between the electrodes leading to high impedance regions and no charge transfer between the electrodes. It is at the border of these areas that lithium metal is deposited. Lithium-ion batteries have the particularity of addressing applications as diverse as mobile electronic devices, electric vehicles or stationary applications of renewable energy. The use of rechargeable electrochemical cells is first and foremost a question of autonomy, lifetime and safety.1-3 So it is necessary to further increase the current performance of lithium-ion batteries.Deposition of metallic lithium or "lithium plating" is one of the aging mechanisms that is limiting the lifetime of lithium-ion batteries. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In the literature, it is reported that the mechanism of lithium deposition generally occurs during the charge at low temperatures and/or at high current-rates. The intercalation of lithium ions into the structure of the negative electrode is in competition with the deposition of metallic lithium on top of the Solid Electrolyte Interphase (SEI). The morphology of the negative electrode, the porosity, the conductivity of the electrolyte and the state of lithiation are parameters to be considered. 8 This aging mechanism depends on intrinsic criteria of the components of the cell (active material, electrodes and electrolyte composition [21][22][23][24][25][26][27][28][29][30] ) and extrinsic to the system (temperature and charging current).Contact between the deposited lithium and the electrolyte (above the surface of the SEI) leads to the oxidation of lithium to form species such as ROCO 2 Li, Li 2 CO 3 or LiF. 15 The deposited lithium becomes isolated and electrochemically inactive and cannot participate in the electrochemical process at the electrodes. The deposit can grow in height from graphite particles and form dendrites which can pass through the separator and cause short circuit. This phenomena in combinatio...

Study of Li Metal Deposition in Lithium Ion Battery during Low-Temperature Cycle Using In Situ Solid-State7Li Nuclear Magnetic Resonance

“…The peaks observed in these spectra are assigned as follows: the electrolyte appears at approximately 0 ppm, Li stored in the negative electrode material (as a GIC) appears at approximately 40 ppm, and deposited Li metal appears at approximately 265 ppm. 15 The NMR method clearly detected the Li metal deposition and Li storage in the negative electrode quantitatively. The Li metal peak increased and the GIC peak decreased as the cycling persisted in all temperature conditions.…”

“…Li metal deposition has also been evaluated by weighing the electrode and measuring the nuclear magnetic resonance (NMR) of a commercial 18650 battery after cycling. [14][15][16] However, these studies are post molten analysis with disassembling the cell and affected the results by sample preparation. 17 Furthermore, deposited Li metal sometimes intercalates into graphite, thus missing the chance to acquire a true sample.…”

Identification and characterization of the dominant thermal resistance in lithium-ion batteries using operando 3-omega sensors

“…If this results from CO 2 being formed at the cathode from oxalate and consumed at the anode by the reverse reaction, one would expect the reaction to happen near the surface of both electrodes and result in the accumulation of gas at both electrodes. The progressive formation of gas bubbles can cause a contact disconnection between the electrodes and the separator 30 . This local delamination leads to areas of dry-out resulting in loss of capacity and regions of high impedance [30][31][32] .…”

“…The progressive formation of gas bubbles can cause a contact disconnection between the electrodes and the separator 30 . This local delamination leads to areas of dry-out resulting in loss of capacity and regions of high impedance [30][31][32] . More research is needed to incorporate the effects of cycling into the TCR model.…”

Low-temperature aging mechanisms of commercial graphite/LiFePO4 cells cycled with a simulated electric vehicle load profile—A post-mortem study

“…In the literature, most of the post-mortem studies conducted for low-temperature cycled cells have employed an accelerated aging scheme using constant currents in the cycle aging of the cells [11,12,[14][15][16][17][18][19][21][22][23]. However, for example Klett et al [26] have shown that constant current cycling (3.75C) in a wide SoC range results in significantly more severe degradation of the cell performance than a simulated HEV bus cycle (max.…”