Extended cycle life implications of fast charging for lithium-ion battery cathode

of the global EV market, Li-ion battery (LIB) technology has progressed to meet the demand for longer driving ranges and extended service lives, while increasing the thermal stability and reducing the cost of the battery. As the performance of LIBs is largely determined by the cathode material, the development of high-performance LIBs for EVs has focused on increasing the capacity of the cathode by usingHowever, cathodes with a high Ni content suffer from inherent structural and chemical instabilities, which lead to rapid capacity fading and thermal instability. [3][4][5][6][7][8][9] In particular, the rapid capacity fading of Ni-rich layered cathodes is largely caused by microcracking and the resultant microstructural instability. [9][10][11][12][13][14][15][16][17][18][19] Microcracks create channels through which the electrolyte can infiltrate the cathode particles, which increases the surface area exposed to electrolyte and worsens parasitic electrolyte attack. The subsequent degradation of the internal surfaces accelerates the accumulation of NiO-like impurity layers at the cathode-electrolyte interface, which hinders electrochemical reactions. [9,[19][20][21][22][23][24][25] As microcracking is caused by abrupt contraction of the unit cells during the H2-H3 phase transition at a high state of charge (SoC), microstructural engineering to facilitate the dissipation of internal mechanical strain and mitigate microcracking in the cathode particles has been extensively investigated. [19,21,[24][25][26][27][28][29][30] One such engineered microstructure is a highly oriented microstructure in which elongated primary particles are aligned along the radial direction in the secondary particle periphery. This radial alignment of rod-shaped primary particles effectively dissipates localized strain by allowing the unit cell to contract and expand uniformly. Microstructural manipulation can be achieved by compositional gradient design of transition metal ions [19,24,25,31] or by doping with various atoms (e.g., B, Ta, Mo, W, and Sb) during lithiation. [18,[26][27][28][29][30]32,33] Furthermore, a reduction in volume deformation and internal stress inside the particle via Al doping can enhance the structural integrity and robustness of cathode. [30,34,35] In addition to microcracking, the time during which highly reactive Ni 4+ ions are exposed to the electrolyte when the cathode is in a highly charged state also affects the deterioration of the cathode. Although the exposure time is not Li-ion batteries (LIBs) in electric vehicles (EVs) are usually operated intermittently and maintained at high states of charge (SoCs) for long periods. Because the internal particles of Ni-rich cathodes are easily exposed to the electrolyte at high SoCs owing to mechanical instability, the electrolyte exposure time-during which highly reactive Ni 4+ ions react with the electrolyte-critically affects the degradation of the cathode. Here, 1 mol% B doping of a core-shell concentration gradient (CSG) Li[Ni 0.88 Co 0.10 Al 0.02 ]O 2 cathode (C...

Section: Resultsmentioning

confidence: 99%

High‐Energy Ni‐Rich Cathode Materials for Long‐Range and Long‐Life Electric Vehicles

Namkoong

Park

et al. 2022

“…The NMC811 used in this study has a wider particle distribution of D10 6.4 µm, D50 12.5 µm, and D90 22.92 µm, as compared to the NMC532 of D10 7.1 µm, D50 9.3 µm, and D90 12.1 µm cathode material used in a previous XFC aging study. [ 21 ] Upon formation and degassing at CAMP, the cells were shipped to Idaho National Laboratory (INL) for fast‐charge cycle life evaluation.…”

Section: Methodsmentioning

confidence: 99%

“…[ 8,16–19 ] Additionally, correlating cathode degradation from coin cell studies with actual cell formats used in EVs is challenging as coin cells do not have comparable impedance, utilization behavior, and life expectancy to EV relevant cells. [ 20–22 ]…”

Section: Introductionmentioning

confidence: 99%

“…later noted that NMC532 cathode aging issues remain minimal in early cycling and become more apparent in later cycles, irrespective of charging rate when charge acceptance was kept above 90%. [ 21 ] Tanim et al. 's study also concluded that inter‐primary particle (IPP) separation (or cracking) within the secondary particles is the main cause of NMC532 cathode degradation along with minor surface reconstruction.…”

Section: Introductionmentioning

confidence: 99%

“…'s study also concluded that inter‐primary particle (IPP) separation (or cracking) within the secondary particles is the main cause of NMC532 cathode degradation along with minor surface reconstruction. [ 21 ] Continuum‐level damage models [ 25 ] predicted that particle architecture (including secondary particle size and morphology) and grain architecture (including grain size and orientation) strongly influence the chemo‐mechanical electrode response. The models found that high‐rate cycling induces significantly more strain due to surface‐level lattice strain induced by Li gradients.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Tanim

Yang

Finegan

et al. 2022

Self Cite

As the battery industry shifts toward high Ni content cathodes, such as LiNi0.8Mn0.1Co0.1O2 [NMC811], a complete understanding of the degradation mechanisms of NMC811 under extreme fast charging (XFC) (XFC, ≤10–15 min charging) conditions is needed. Such comprehensive understanding would identify the most critical materials gaps that need to be addressed for enabling XFC long‐life cells for electric vehicles. This study maps out the key aging mechanisms for NMC811 cycled at different XFC conditions (between 1C and 9C) for up to 1000 cycles. To acquire a fundamental understanding of utilization and degradation, cells are evaluated using a range of electrochemical techniques, and multimodal and multiscale microscopy techniques to quantify chemical, structural, and crystallographic degradation as a function of cycling conditions for the NMC cathode. When comparing NMC811 to NMC532, it is observed that NMC811 has a greater subsurface crystallographic degradation and displays a similar magnitude of subparticle cracking. However, the NMC811 maintains superior performance despite those advanced degradations. The superior cycle life performance is attributed to the NMC811 particles having radially oriented grains and improved transport properties. NMC811 shows between 4.6× and 3.15× reduction in capacity fade than NMC532 for charging rates between 4C (e.g., 15‐min charging) and 6C (10‐min charging).

Enabling Extreme Fast‐Charging: Challenges at the Cathode and Mitigation Strategies

Tanim

Weddle

Yang

et al. 2022

Self Cite

Charging lithium‐ion batteries (LiBs) in 10 to 15 min via extreme fast‐charging (XFC) is important for the widespread adoption of electric vehicles (EVs). Lately, the battery research community has focused on identifying XFC bottlenecks and determining novel design solutions. Like other LiB components, cathodes can present XFC bottlenecks, especially when considering long‐term battery life. Therefore, it is necessary to develop a comprehensive understanding of how XFC conditions degrade LiB cathodes. The present article reviews relevant cathode‐focused studies and summarizes the current understanding regarding cathode performance and aging issues under XFC conditions. Dominant aging modes and mechanisms are identified at different length‐scales with electrochemical correlations for LiNixMnyCozO2 (NMC)‐based cathodes. A range of electrochemical techniques and models provide key insights into cathode performance and life issues. A suite of multimodal and multiscale microscopy and X‐ray techniques is surveyed to quantify chemical, structural, and crystallographic NMC‐cathode degradation. Cathode cycle‐life is scaled to equivalent EV miles to illustrate how cathode degradation translates to real‐world scenarios and quantifies cathode‐related bottlenecks that hinder XFC adoption. Finally, the article discusses several cathode cycle‐life aging mitigation strategies with example case studies and identifies remaining challenges.