Fast lithium growth and short circuit induced by localized-temperature hotspots in lithium batteries

Abstract

Fast-charging and high-energy-density batteries pose significant safety concerns due to high rates of heat generation. Understanding how localized high temperatures affect the battery is critical but remains challenging, mainly due to the difficulty of probing battery internal temperature with high spatial resolution. Here we introduce a method to induce and sense localized high temperature inside a lithium battery using micro-Raman spectroscopy. We discover that temperature hotspots can induce significant lithium metal growth as compared to the surrounding lower temperature area due to the locally enhanced surface exchange current density. More importantly, localized high temperature can be one of the factors to cause battery internal shorting, which further elevates the temperature and increases the risk of thermal runaway. This work provides important insights on the effects of heterogeneous temperatures within batteries and aids the development of safer batteries, thermal management schemes, and diagnostic tools.

Fig. 1

Experimental setup. a Schematic (not to scale) of a modified coin cell with an optically transparent glass window for laser access to graphene as a temperature indicator and the thermally evaporated Cu current collector. b G-band Raman peak position of the graphene as a function of the temperature. The temperature coefficient was obtained from the slope of the linear fit (dashed line). The inset shows the schematic of the calibration setup. c Temperature of the hotspot on Cu generated by a 532 nm laser in a coin cell as a function of the laser power. The dots are experimental results and the solid line is from thermal simulation in COMSOL Multiphysics

Fig. 2

Lithium deposition on hotspots. SEM images (top-down view) of Li deposited on Cu with hotspot temperatures of a 51 °C at a laser power of 6.7 mW, b 83 °C at 13.4 mW, and c 99 °C at 16.8 mW, respectively. The corresponding (cross-sectional view) temperature distribution from simulation near the laser spot with powers of d 6.7 mW, e 13.4 mW, and f 16.8 mW. The simulated Li deposition rate on the Cu surface (top-down view) with laser heated hotspot temperatures of g 51 °C at 6.7 mW, h 83 °C at 13.4 mW, and i 99 °C at 16.8 mW, respectively

Fig. 3

Hotspot-induced battery shorting. a Schematic of an optical cell with Cu and lithium cobalt oxide (LCO) as the electrodes. b Cell voltage as the battery was charged at a constant current of 30 μA. After onset of shorting, the voltage started to drop and fluctuate. Visualization of Li-plating process initially at c t₀ = 0 s, before shorting at d t₁ = 760 s, e t₂ = 1160 s, onset of shorting at f t₃ = 1480 s, and after shorting at g t₄ = 1800 s

Fig. 4

Hotspot-induced battery shorting and local-temperature response. a Schematic of the optical cell with a resistance temperature detector (RTD) in the copper-LCO (lithium cobalt oxide) gap and a laser hotspot. b Calibration of the RTD resistance as a function of the temperature. The dots are experimental measurements and the line is linear fit. c Current (left axis) of the battery and temperature response (right axis) measured by the RTD