Lithium transport through lithium-ion battery cathode coatings

Abstract

The surface coating of cathodes using insulator films has proven to be a promising method for high-voltage 10 cathode stabilization in Li-ion batteries, but there is still substantial uncertainty about how these films function. More 11 specifically, there is limited knowledge of lithium solubility and transport through the films, which is important for coating 12 design and development. This study uses first-principles calculations based on Density Functional Theory to examine the 13 diffusivity of interstitial lithium in the crystals of α-AlF3, α-Al2O3, m-ZrO2, c-MgO, and α-quartz SiO2, which provide benchmark 14 cases for further understanding of insulator coatings in general. In addition, we propose an Ohmic electrolyte model to predict 15 resistivities and overpotential contributions under battery operating conditions. For the crystalline materials considered we 16 predict that Li + diffuses quite slowly, with a migration barrier larger than 0.9 eV in all crystalline materials except α-quartz SiO2, 17 which is predicted to have a migration barrier of 0.276 eV along <001>. These results suggest that the stable crystalline forms of 18 these insulator materials, except for oriented α-quartz SiO2, are not practical for conformal cathode coatings. Amorphous Al2O3 19 and AlF3 have higher Li + diffusivities than their crystalline counterparts. Our predicted amorphous Al2O3 resistivity (1789 MΩm) is 20 close to the top of the range of the fitted resistivities extracted from previous experiments on nominal Al2O3 coatings (7.8 to 913 21 MΩm) while our predicted amorphous AlF3 resistivity (114 MΩm) is very close to the middle of the range. These comparisons 22 support our framework for modeling and understanding the impact on overpotential of conformal coatings in terms of their 23 fundamental thermodynamic and kinetic properties, and support that these materials can provide practical conformal coatings 24 in their amorphous form.25 I. Introduction 26 27 Surface modification of the cathode by artificial coating is an effective strategy to stabilize Li-ion batteries (LIBs) 28 operating at high voltages.[1-10] Nevertheless, the coating functionalities and the stabilizing mechanisms are still not 29 fully understood and currently a subject of intensive research in the development of next-generation LIBs. Several 30 roles for the coating have been proposed to account for its positive impacts on the cathode performance, including: (i) 31 electrical conduction medium that facilitates electron transport between cathode active particles,[11] (ii) modifier of 32 cathode surface chemistry that changes chemical properties of the cathode surface to improve stability and 33 performance,[12] (iii) HF scavenger that locally reduces the acidity of the electrolyte near the cathode surface, thereby 34 reducing electrolyte degradation,[13-15] and (iv) physical protection barrier that suppresses electrolyte oxidation and 35 cathode corrosion. [8,[16][17][18][19][20] In general, role (iii) and, particularly, role (iv) are the most widely cl...

High-throughput computational design of cathode coatings for Li-ion batteries

“…Electronic and Li-ion conductivity are the two other important factors in coating design as addressed in recent studies5960, both of which should be high enough to have an effective coating material that does not result in large interfacial impedance and improves the electrochemical performance of the battery. These properties, however, strongly depend on extrinsic factors such as the morphology, microstructure and synthesis conditions, and therefore are hard to model and show significant variations.…”

“…These properties, however, strongly depend on extrinsic factors such as the morphology, microstructure and synthesis conditions, and therefore are hard to model and show significant variations. For example, Xu et al 60. showed that most of the common coating materials do not allow adequate Li ion transport in crystalline form whereas their amorphous counterparts often provide fast enough Li + diffusion that allows effective conformal coating morphologies5960.…”

Multifunctional modification of Li[Ni0.5Co0.2Mn0.3]O2 with NH4VO3 as a high performance cathode material for lithium ion batteries

“…Surface coating can do a great benefit on the surface structure of electrode material and change the property of solid-liquid interface [15][16][17]. Up to now, there have been a number of metal oxides and fluorides acting as feasible coating materials [18][19][20][21][22][23][24].…”

Nanoscale Voltage Enhancement at Cathode Interfaces in Li-Ion Batteries

“…Moreover, interfaces inevitably occur for cathode particles at their surface, either with a solid electrolyte interphase (SEI) or frequently a protective coating layer, the latter of which is typically comprised of insulating metal oxides or fluorides [7][8][9][10][11][12][13][14][15] or sometimes an electrochemically active material (e.g., Li-Ni-PO 4 coating layer) 16 .…”