Importance of Thermal Transport for the Design of Solid-State Battery Materials

Perspective
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Importance of Thermal Transport for the Design of Solid-State Battery Materials

Matthias T. Agne, Thorben Böger, Tim Bernges, and Wolfgang G. Zeier

PRX Energy 1, 031002 – Published 22 December 2022

Abstract

Battery technologies have evolved rapidly over the past decade, including the advent of solid-state batteries. In this time, it has become apparent that thermal management is paramount for device operation and lifetime. However, the fundamental importance of the thermal properties of materials, such as thermal conductivity, in engineering design and mitigating the risk of catastrophic failure is yet to be fully understood. This Perspective aims to provide motivation for the fields of thermal transport and ionic transport to join forces to understand heat transport for better battery design, especially in light of solid-state batteries. From the basic characterization of thermal conductivity in bulk materials to considering the full complexity of battery composites during electrochemical cycling, there are many potential directions for fundamental and applied investigations. We anticipate that studying heat transport in battery materials has the added benefit of extending the design space to other functional devices. The difficulty in controlling heat transport in solid-state energy devices, including microelectronics, batteries, and thermoelectrics, is often a limiting factor in improving device performance. Especially in batteries, not only can excessive heat cause degradation that leads to a loss of charge capacity over time, but thermal runaway can occur when the battery overheats to catastrophic failure. Thus, understanding heat evolution and thermal transport in batteries is an important step to improve lifetime and safety. It is from this perspective that we provide the motivation for the importance of bringing together the fields of thermal transport and battery research, particularly to study solid-state batteries, which epitomize the overall complexity of battery systems and require a state-of-the-art understanding of thermal transport mechanisms. Here, we identify the basic and applied scientific directions that may prove fruitful for the next generation of battery thermal management.

Received 22 September 2022
Revised 4 December 2022

DOI:https://doi.org/10.1103/PRXEnergy.1.031002

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Batteries Energy materials Energy transport Solid-state batteries Thermal properties Thermoelectric generators

Energy Science & Technology

Authors & Affiliations

Matthias T. Agne ¹, Thorben Böger^1,2, Tim Bernges¹, and Wolfgang G. Zeier ^1,3,*

¹Institute of Inorganic and Analytical Chemistry, University of Münster, 48149 Münster, Germany
²International Graduate School for Battery Chemistry, Characterization, Analysis, Recycling and Application (BACCARA), University of Münster, 48149 Münster, Germany
³Institut für Energie- und Klimaforschung (IEK), IEK-12: Helmholtz-Institut Münster, Forschungszentrum Jülich, 48149 Münster, Germany

^*wzeier@uni-muenster.de

Popular Summary

Solid-state energy devices, such as batteries, microelectronics, and thermoelectrics, face performance limitations due to difficulties in controlling heat transport. In batteries, excessive heat can not only cause degradation that leads to a loss of charge capacity over time, but thermal runaway can also occur when the battery overheats to catastrophic failure. Thus, understanding heat evolution and thermal transport is an important step to improve lifetime and safety of batteries. It is from this perspective that the authors provide the motivation for bringing together the fields of thermal transport and battery research. In particular, solid-state batteries epitomize the complexity of battery systems and require a state-of-the-art understanding of thermal transport mechanisms. Here, the authors identify the basic and applied scientific directions that may prove fruitful for the next generation of battery thermal management.

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Vol. 1, Iss. 3 — December - December 2022

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Figure 1
(a) Solid-state battery configuration with a lithium metal anode (pale yellow); a solid ionic conducting separator (beige circles); and a composite cathode (yellow and orange circles) consisting of ionic conductors, cathode active materials, and potential additives. Variety of interfaces are highlighted at which heat generation may be expected. (b) Schematic of a potential temperature distribution snapshot in the solid-state battery [shown in panel (a)] during operation. Goal of multiscale material modeling is to enable reliable calculation of such heat maps to inform device design.
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Figure 2
Phonon character and thermal transport behavior. Schematic phonon dispersion in which acoustic (blue) vibrational modes are highly dispersive and distinct, resulting in gaslike phonon transport of vibrational energy $ℏ ω$ , whereas optical (pink) vibrational modes have little dispersion and a high degree of (quasi-)degeneracy, which gives rise to diffusonlike hopping transport of vibrational energy $ℏ ω$ as an atomic scale random walk.
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Figure 3
Characterization of thermal transport. (a) Temperature dependence of thermal conductivity for a variety of active materials [46, 47, 48] and solid electrolytes [46, 49] reveals that diffusonlike vibrational character may be prevalent. Compared to the thermal conductivity of liquid electrolytes (∼0.2 W m⁻¹ K⁻¹ at 300 K) [46], solid electrolytes may not offer much of an improvement. (b) State-of-charge dependence of thermal conductivity is due to the changing content of mobile ions in the active materials [50, 51], structural changes, and any additional microstructural effects, which are a potential cause of the hysteretic behavior. (c) Chemical design space for battery materials, illustrated here considering ${Li Ni}_{x} {Mn}_{y} {Co}_{z} O_{2}$ cathode materials, is currently being explored for electrochemical performance and cost optimization; however, (d) the magnitude of thermal conductivity is also expected to depend on material composition, as demonstrated here in ${Li Ni}_{x} {Mn}_{y} {Co}_{z} O_{2}$ cathode materials (figure after Ref. [48]) with a constant lithium content. Thus, future battery development needs to include thermal management considerations when thermal properties are characterized.
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Figure 4
Vibrational understanding of ionic transport. (a) Schematic of the lowest energy pathway for a mobile ion to move between crystallographic sites. (b) Single low-frequency phonon mode, where phonon eigenvectors indicate a displacive motion of mobile ions along the jump pathway shown in panel (a). (c) By analyzing the phonon eigenvectors for all of the mobile ion vibrational modes, it is possible to see the spectral density of states of vibrations that contribute to the net motion of the mobile ion along the jump pathway. (d) Bose-Einstein distribution gives the average number of thermal phonons expected to be populated at a given temperature and vibrational mode energy (frequency), where lower frequency modes have higher average phonon occupations; however, the instantaneous occupation of phonons in a vibrational mode is a fluctuating quantity and the probability of a given number of phonons follows a Boltzmann distribution (see the color map). Also shown is the number of phonons that would be required in a given phonon mode to achieve a thermal energy of 0.3 eV, which is a typical activation barrier energy for ion transport in fast ion conductors.
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