# Analyzing the coupling characteristics of real-time key parameters in the thermal runaway of NCM523 batteries

## TL;DR

This study explores how NCM523 lithium-ion batteries experience thermal runaway, focusing on gas production and flame behavior under different charging conditions.

## Contribution

The work identifies four stages of thermal runaway and clarifies gas-flame coupling mechanisms under low-power heating.

## Key findings

- Deflagration is mainly triggered by CO and H2 from polyvinylidene fluoride decomposition at 260°C.
- High-SOC batteries show significant deflagration, while low-SOC ones have variable combustion duration and mass fluctuation.
- The study provides theoretical support for improving NCM523 battery safety and fire suppression.

## Abstract

Lithium-ion batteries (LIBs) based on LiNi0.5Co0.2Mn0.3O2 (NCM523) are widely used in electric vehicles, yet thermal runaway (TR) remains a critical safety challenge. In real battery packs, materials filled between batteries reduce heat transfer during TR, frequently inducing a low-power heating phenomenon that is prevalent yet not fully understood, hindering the development of effective TR suppression and hazard mitigation strategies. Herein, this work investigates NCM523 LIBs’ TR characteristics via low-power heating experiments, delineating TR into four stages and identifying key gaseous products. Deflagration is mainly triggered by CO and H2 from polyvinylidene fluoride decomposition at 260°C, with flame behaviors strongly dependent on state of charge (SOC): high-SOC (>60%) batteries show significant deflagration, while low-SOC ones exhibit variable combustion duration and larger residual mass fluctuation. This work clarifies the gas-flame coupling mechanisms, addresses existing research deficiencies, and provides theoretical support for NCM523 LIB safety design and fire-suppression optimization.

•Accurate internal temperature assessment before battery thermal runaway (TR)•Analysis of the mechanism of TR induced by low-heating•Real-time smoke and gas characteristics during the TR process

Accurate internal temperature assessment before battery thermal runaway (TR)

Analysis of the mechanism of TR induced by low-heating

Real-time smoke and gas characteristics during the TR process

Energy systems; Thermal engineering; Energy storage