Deciphering the Role of Binder Reaction Exothermicity in Thermal Runaway of Lithium-Ion Cells

Abstract

Thermal safety associated with lithium-ion cells as power sources remains a critical industry concern. A comprehensive understanding of how internal exothermic side reactions contribute to temperature rise is fundamental for accurately analyzing thermal runaway processes and predicting the thermal safety of lithium-ion cells. While various side-reactions, such as decomposition of solid electrolyte interphase layer, reaction between anode materials and electrolyte, reaction between cathode materials and electrolyte, and electrolyte decomposition, have been identified as heat generation sources in previous studies, the quantification of these reactions remains insufficiently standardized. Particularly, the impact of heat generation from binder decomposition (most commonly polyvinylidene difluoride) at elevated temperatures on the thermal runaway process of lithium-ion cells has not been fully elucidated. Therefore, in this study, an electro-thermal coupled numerical model was developed for 18650-type lithium-ion cells to systematically investigate the synergistic effects of these five major side-reactions under high-temperature conditions leading to thermal runaway. Special emphasis was placed on precisely quantifying the contribution from binder decomposition heat during the thermal runaway process. The results demonstrate that once the ambient temperature exceeds the threshold required to initiate cascading exothermic side reactions, the inclusion or exclusion of the binder reaction in the model does not affect the overall assessment results of thermal runaway for lithium-ion cells. However, under these conditions, the heat contribution from binder decomposition to the total heat release increases significantly and therefore becomes one of the dominant heat sources for temperature rise during the thermal runaway propagation. Conversely, when ambient temperatures do not reach the threshold, the heat contribution from binder decomposition is negligible. Additionally, the improved electro-thermal coupling model serves as an effective simulation tool for designing battery systems with enhanced safety, selecting appropriate binder materials to mitigate the adverse effects of thermal runaway, and optimizing thermal management during battery development. This approach significantly reduces the research and development cycle. These findings establish appropriate heat source selection criteria for electro-thermal models under varying precision requirements and provide a theoretical foundation for both model simplification and high-fidelity optimization in lithium-ion battery design.

Keywords

Electrochemistry / Lithium-ion battery / Mathematical modeling / Thermal runaway / Binder decomposition

Nomenclature

A——frequency factor, s^-1

c——lithium-ion concentration‌, mol·m^-3

c^*——dimensionless amount,

C_p——heat capacity, J/(kg·K)

DR——degree of side reaction,

E——electric potential, V

E_eq——equilibrium potential‌, V

E_a——activation energy, J·mol^-1

F——Faraday constant, C·mol^-1

h——convective heat transfer coefficient, W/(m²·K)

H——heat release per unit mass, J·kg^-1

j——electrode current density, A·m^-3

K——thermal conductivity‌, W/(m·K)

M——specific components content, kg·m^-3

Q——reaction heat, W·m^-3

Q_p——polarization heat, W·m^-3

Q_r——reversible entropic heat, W·m^-3

Q_j——joule heat, W·m^-3

R——gas constant, J/(mol·K)

S_a——active specific surface, m²·m^-3

t——time, s; temperature, ℃

t_{+}^0——lithium-ion transference number,

T——temperature, K

T_∞——ambient temperature, K

W——cumulative heat release, J

z——SEI dimensionless thickness,

Greek symbols

κ——ionic conductivity‌, S·m^-1

ρ——density，kg·m^-3

σ——electron conductivity, S·m^-1

φ——electric potential, V

Subscript

0——initial value

e——liquid electrolyte

ele——electrolyte decomposition

neg——anode decomposition

ref——reference state

pos——cathode decomposition

pvdf——binder reaction

s——solid phase

sei——SEI decomposition

‌Superscript

eff——effective value‌

Conflict of Interests

The authors declare no conflicts of interest.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (No. 22178102).

Data Availability

Data will be made available from the corresponding author on reasonable request.

Author Contributions

Wen Wen: Methodology, Writing-original draft, Writing-review & editing; Jing-Hong Zhou: Project administration, Conceptualization, Writing-review& editing; Hao-Tian Lu: Methodology, Investigation; Xing-Gui Zhou: Supervision

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