Thermal Analysis of LiNi_0.4Co_0.2Mn_0.4O₂/Mesocarbon Microbeads Cells and Electrodes: State-of-Charge and State-of-Health Influences on Reaction Kinetics

Abstract

The thermal stability of lithium ion batteries was studied by means of Accelerating Rate Calorimetry in Heat-Wait-Search operation on both electrode and cell level. Fresh and aged samples were investigated depending on the state-of-charge (SoC) of a 5 Ah pouch cell comprising mesocarbon microbeads and LiNi 0.4 Co 0.2 Mn 0.4 O 2 as the anode and cathode materials. 1 M LiPF 6 in EC:DEC 3:7 (by weight) containing 2 wt% VC and 0.5 wt% LiBOB was chosen as the electrolyte. Measurements on the electrode level revealed a higher self-heating rate (SHR) of the cathode compared to the anode for all SoC and state-of-health (SoH) combinations in the temperature range where a self-sustaining decomposition reaction could be detected. A lower SoC showed a lower SHR of the electrode/electrolyte mixture with no reaction detected on the anode side ≤ 50% cell SoC. Cyclic aging led to a decrease in thermal stability of the cathode at lower SoC values with no significant influence on the anode implying a larger safety threat on the cell level. Avrami-Erofeev and autocatalytic reaction models were used to quantify the influences of SoC and SoH on reaction kinetics. Based on their high energy and power density combined with a long cycle life, high energy efficiency and low costs, lithium ion batteries are currently the state-of-the-art energy source for electric vehicles (EV). 1-3 A long cycle life requires excellent aging behavior, whereas a high energy and power density demands for a high level of safety in order to comply with automotive prerequisites. [4][5][6] Many studies have dealt with the investigation of aging and safety individually as well as their interplay. 4,[7][8][9][10][11][12][13] Yet, these interactions are not fully understood. Accelerating Rate Calorimetry (ARC) has been reported to be a promising method to measure the thermal stability of samples under quasi-adiabatic conditions. This method can be applied from single battery materials [14][15][16][17][18][19][20] up to full cells. 11,13,21 Based on the prevailing quasi-adiabatic conditions, a worst-case scenario can be simulated. With no heat dissipation taking place, the generated heat can be evaluated by measuring the temperature increase of the sample, knowing its total heat capacity. 22 This behavior can be readily transferred to real life scenarios where heat dissipation during cell failure is partially inhibited by the cell surroundings.Predicting a cell's behavior during thermal abuse conditions is a topic of major interest in order to prevent hazardous situations on the battery pack level such as the propagation of thermal runaway after a single cell failure. 23 Due to the complexity of cell thermal runaway dynamics influenced e.g. by material composition 14,15 and morphology, [24][25][26] modeling and simulation can help to identify the dominating processes and interactions within a single cell based on individual material decomposition reactions. [27][28][29] Characteristic kinetic parameters of predominantly empirical decomposition reaction models were...

Quasi-Isothermal External Short Circuit Tests Applied to Lithium-Ion Cells: Part II. Modeling and Simulation

“…Recently, the applicability of the modeling approach to also describe large current densities occurring during abusive short circuit events has been discussed 33,34 but not validated. Provided that no further phenomena such as a possible deviation from electro-neutrality (at high currents or low salt concentrations 61 ), solvent convection (at high salt concentrations and concentration gradients 62 ), salt precipitation (at high salt concentrations 28 ) or thermal decomposition reactions (at high temperatures 55,63,64 ) are dominating the cell behavior and as long as the model equations can be solved without facing numerical issues, in theory the model should be also valid for describing a cell's response during hard external short circuit tests. Based on the theories of porous electrodes and concentrated solutions, 60 the applied pseudo two-dimensional (p2D) model accounts for a material balance and Ohm's law within both solid and liquid components as well as a charge balance based on Butler-Volmer reaction kinetics which can be summarized in five partial differential equations.…”

“…Such a combined modeling approach might help to identify critical short circuit conditions, which could result in the occurrence of thermal decomposition reactions and ultimately thermal runaway at a certain combination of temperature and SoC reached throughout the short circuit. 64 This information could be further used to design cells and electrodes depending on the topology of the battery pack with its inherent thermal management system in order to maximize the short circuit tolerance of the entire battery system.…”

Quasi-Isothermal External Short Circuit Tests Applied to Lithium-Ion Cells: Part I. Measurements

“…Furthermore, the thermal behavior during battery failure is not only dependent on the chemical composition of the active and passive materials used within the cells, 22,23 but also affected by the state of charge (SoC) and state of health (SoH) of the cell and the respective electrodes. 24,25 A dedicated experimental investigation enabling a separation of effects is required for understanding the underlying mechanisms during a short circuit event. This accounts for both internal as well as external short circuits, whereas the focus of this work is laid on the latter in order to study the overall short circuit behavior of a battery in the first place.…”

Degradation of Lithium-Ion Batteries in an Electric Transport Complex

“…However, studies of carbon materials for lithium-ion batteries are still ongoing, with special attention paid to various nanofiber materials, nanotubes, nanocomposites, graphene nanoparticles, etc. [97]…”