conversion mechanism of nickel fluoride and nio-doped nickel fluoride in li ion batteries.doc

Conversion mechanism of nickel fluoride and NiO-doped nickel fluoride in Li ion batteries Electrochimica Acta 59 (2021) 213– 221Contents lists available at SciVerse ScienceDirectElectrochimica Actajou rn al hom epa ge: elsevier /locate/electactaConversionLi mechanism of nickel fluoride and NiO-doped nickel fluoride in ion batteriesDae Hoe Leea, Kyler J. Carrolla, Scott Calvinb, Sungho Jina, Ying Shirley Menga,?aDepartmentbDepartment of NanoEngineering, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA of Physics, Sarah Lawrence College, Bronxville, NY 10708, USAa r t i c l e i n f oArticleReceivedReceivedAcceptedAvailable online 9 November 2021 history: 19 July 2021 in revised form 15 October 2021 20 October 2021Keywords:ConversionNickelNiO-dopedNucleationSuperparamagnetism mechanism fluoride nickel fluoride and growth of Nia b s t r a c tTheusingtroscopyinterferenceodeexhibitedtogestedtheexparticlessuperparamagneticsize conversion mechanism of NiF2and NiO-doped NiF2during electrochemical cycling was investigated a combination of structural analysis by ex situ X-ray diffraction (XRD), X-ray photoelectron spec- (XPS), X-ray absorption spectroscopy (XAS) and magnetic analysis by superconducting quantum device (SQUID) magnetometry. It was observed that the conversion reactions in both cath- materials were partially reversible; however, they differ in their conversion rate. NiO-doped NiF2 enhanced electrochemical properties in terms of the conversion potential and reversibility due the presence of a NiO phase, which has slightly higher electronic conductivity than NiF2. It is sug- that the NiO doping reduced the nucleation sites for Ni nanoparticles, subsequently enhancing kinetics of the conversion reaction involving the growth of Ni particles formed during lithiation. The situ XRD and the magnetic hysteresis data (HCand MS) indicate that the average dimension of the Ni formed along with LiF in pristine NiF2and NiO-doped NiF2during the 1st lithiation was in the regime, with 4–5 nm and 8–9 nm particle sizes, respectively. Although the particle was decreased to the nanoscale, the original NiF2phase was regenerated? 2021 Elsevier Ltd. All rights reserved. by re-lithiation.1. IntroductionThe lithium ion battery is one of the most important recharge-ablecycleionsourcesionstillingChoosingoftheassociatedmaterials,capacitiesasmaterialsoftheintercalation-based energy storage devices, since it has a high energy density, long life, high working cell potential and reliable safety. Lithium batteries are also one of the leading candidates for the power in electric vehicles. Although the performance of lithium batteries has been improving rapidly in recent years, there are several issues that need to be resolved for applications requir- higher energy density. the best cathode material used in a Li-ion battery is one the most crucial issues in achieving higher energy densities, since energy density is directly correlated to the specific capacity with that cathode material [1]. The intercalation-based such as LiFePO4, LiMn2O4, and LiCoO2 with specific ranging from 100 to 150 mA h g?1are widely utilized the positive electrode of commercial Li-ion batteries. These exhibit excellent cycling properties since the structure the cathode materials are not significantly changed during intercalation and de-intercalation of lithium ions [2]. The materials, however, yield only a limited spe-?CorrespondingE-mail author. Tel.: +1 8588224247; fax: +1 8585349553. address: shmeng@ucsd.edu (Y.S. Meng).cificvalenceovercometotiallyredoxcan capacity because of the structure and corresponding restricted changes of the transition metals. This insufficiency can be by utilizing conversion based cathode materials that tend exhibit substantially higher capacities, due to the fact that essen- all the possible oxidation states of the compound during the reaction can be utilized [3]. The overall conversion reaction be summarized as the following:Mn+X + nLi++ ne?? nLiXX + M (M = Co, Fe, Ni, Cu, etc.; = F, O, S, N, etc.) (1)The conversion type materials have been studied as potentialelectrodegroupweretiesHowever,electrodes,thanTransitionpotential[6–9].itedaet materials for high energy lithium ion batteries. Tarascon’s first demonstrated that these conversion materials, which Co3O4, CoO, NiO, and FeO, can exhibit high specific capaci- of 600–1000 mA h g?1along with good cycling properties [3–5]. these metal oxides are only suitable for use as negative due to their low conversion potential, which is lower 1.0 V. metal fluorides have recently been investigated as cathode materials because of their high electronegativity However, the insulating nature of metal fluorides has lim- their electrochemical properties for a long time; for that reason considerable amount of attention has been devoted by Badway al. [10–12], to tailoring their nanostructures to overcome poor0013-46。