Thermal Reactions Between Delithiated Lithium Nickelate and Electrolyte Solutions

Abstract

Lithium nickelate is a promising electrode material for lithium-ion batteries, however, its low thermal stability is a problem that should be solved. We studied the thermal stability of delithiated lithium nickelate compounds in the presence of electrolyte solvents/solutions. We measured the exothermal heat generation of the reaction system using differential scanning calorimetry. We examined simple systems such as ethylene carbonate with Li 0.2 NiO 2 , using hermetically sealed pans that allowed us to perform the experiments under constant mass conditions. The data were quantitatively analyzed to propose possible reaction mechanisms for the exothermal behavior. We attributed the main source of the exothermal heat to organic solvent combustion caused by oxygen released from the nickelate. We studied similar reactions using other solvents/solutions and electrochemically or chemically delithiated nickelate samples. We also examined the behavior of lithium cobaltate for comparison. We discuss the effect of partial substitution for nickel on thermal stability.Lithium nickelate is an attractive positive electrode material for lithium-ion batteries because of its comparatively low cost and large capacity. 1-3 However, its stability must be improved to meet safety standards, because highly delithiated compounds Li x NiO 2 (xϹ0.3) decompose exothermally at around 200°C. 4-6 It has recently been reported that there is even greater exothermal heat generation when the nickelate material is heated in the presence of organic electrolyte solutions. 7-15 However, the origin of this large heat generation has remained unclear because of the complexity of the reaction system, which contains many components such as electrode material, electrolyte solute, and mixed organic solvents. For examining such thermal behavior, differential scanning calorimetry ͑DSC͒ has been widely used. 5-17 As DSC shows the amount of generated heat quantitatively, a study of simple reaction systems, for example, oxide with a single solvent, may be the key to discovering the reaction mechanism.In this study we report the thermal behavior of Li x NiO 2 in contact with electrolyte solutions using DSC coupled with thermogravimetry ͑TG͒. We examined reactions involving ethylene carbonate ͑EC͒ in particular detail, because EC is often used as the main component in electrolyte solutions. We tested both electrochemically and chemically delithiated compounds and compared their behavior with that of lithium cobaltate. We also discuss the effect of partial substitution for nickel on the thermal stability of the delithiated material. ExperimentalWe prepared nearly stoichiometric LiNiO 2 samples by heating a mixture of LiOH•H 2 O, LiNO 3 , and Ni͑OH͒ 2 ͑1:1:1 in molar ratios͒ in air at 500°C for 6 h and then at 700°C for 24 h. We removed unreacted lithium compounds by washing the heated product with distilled water. The structural and electrochemical characteristics of this compound are detailed elsewhere. 18 We used LiCoO 2 powder ͑Nippon Chemical Industrial͒ as rece...

Advanced technology development program for lithium-ion batteries : thermal abuse performance of 18650 Li-ion cells.

“…A sharp exotherm was observed at 225°C followed by a limited but more sustained reaction at 300°C that may have resulted from electrolyte or binder decomposition. Reactions of the partially reacted cathode with electrolyte have also been reported in this temperature region for similar metal oxides [13,14]. The cathode material showed a strong exothermic between 170°C and 190°C, which corresponds to the explosive decomposition regime seen in the thermal ramp experiments.…”

“…The Sony cathode material (LiCoO 2 ) showed the greatest thermal stability with a peak reaction temperature around 225°C. The nickel containing Gen1 cathode material was less stable than the pure cobalt material while the Gen2 cathode (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) was more stable than the Gen1 material (LiNi 0.85 Co 0.15 O 2 ) [13][14][15]. The aluminum doping achieves a small but measurable increase in thermal stability as determined by DSC.…”

“…This high-temperature peak may result from reaction with the PVDF or possibly with additives that are used in these commercial cells. [12][13][14][15]. The cathode exotherm decreased significantly with decreasing SOC.…”

“…The aluminum doping achieves a small but measurable increase in thermal stability as determined by DSC. The exothermic reaction of the cathode is believed to result primarily from combustion of the electrolyte by evolved oxygen from the decomposing cathode oxide [13,14]. The exact nature of the reaction is a function of the inherent stability of the cathode material and relative amounts of cathode and electrolyte [14].…”

Vehicle Battery Safety Roadmap Guidance

“…Work by Dahn and coworkers demonstrated that most cathode chemistries decompose and evolve oxygen. 74 Data on oxygen evolution at elevated temperature have been published for LiCoO 2 , 75 LiNiO 2 , 76 and LiMn 2 O 4 . 77 Oxygen production during high-temperature cathode decomposition is correlated with exotherms observed in ARC experiments.…”