• Energy Research

Cobalt (Co)-free ultrahigh-nickel (Ni) layered oxides exhibit dual competitive advantages in reducing the cathode cost and boosting the energy density, promising the sustainable development of batt...

Cobalt (Co)-free ultrahigh-nickel (Ni) layered oxides exhibit dual competitive advantages in reducing the cathode cost and boosting the energy density, promising the sustainable development of batt...

We report that electrocatalytic water decomposition can be leveraged to enhance the performance of aqueous batteries. Using the NaxFe[Fe(CN)6]ǁNaTi2(PO4)3 aqueous battery as a platform, we demonstrate that electrocatalytic water oxidation can serve as an electrochemical activation approach to achieving higher full cell capacity.

We report that electrocatalytic water decomposition can be leveraged to enhance the performance of aqueous batteries. Using the NaxFe[Fe(CN)6]ǁNaTi2(PO4)3 aqueous battery as a platform, we demonstrate that electrocatalytic water oxidation can serve as an electrochemical activation approach to achieving higher full cell capacity.

The implementation of alkali metal anodes in practical batteries have been unsuccessful due to major safety concerns related to dendritic growth and thermal runaway. Carbon scaffolds have been utilized as promising host materials in an effort to improve battery safety and performance. Herein, “lean” lithium and sodium composite anodes, using a semi-crystalline carbon nanofiber (CNF) host material with limited surface functionalization, are utilized to investigate the relationship between the structural characteristics of the CNF and lithium/sodium metal. Symmetric testing reveals that the Na-CNF composite anode maintains stable cycling performance, with minimal hysteresis increase over 2000 hours, whereas Li-CNF fails before 200 hours. When paired with layered oxide cathodes (NaNi0.33Fe0.3Mn0.33Ti0.04O2 and LiNi0.6Mn0.2Co0.2O2 for sodium and lithium cells, respectively) and cycled at 1C, the Na-CNF cells maintain 75% capacity retention after 500 cycles, but the Li-CNF cells fail shortly after 140 cycles. The primary factor enabling stable long-term cycling for Na-CNF cells is that Na ion undergoes reversible ion intercalation, whereas Li ion is limited to surface adsorption. The inherent carbon crystallinity is found to govern the interaction between the carbon host and alkali metals and is a primary factor in the sustainability and performance of the metal composite anodes.

The implementation of alkali metal anodes in practical batteries have been unsuccessful due to major safety concerns related to dendritic growth and thermal runaway. Carbon scaffolds have been utilized as promising host materials in an effort to improve battery safety and performance. Herein, “lean” lithium and sodium composite anodes, using a semi-crystalline carbon nanofiber (CNF) host material with limited surface functionalization, are utilized to investigate the relationship between the structural characteristics of the CNF and lithium/sodium metal. Symmetric testing reveals that the Na-CNF composite anode maintains stable cycling performance, with minimal hysteresis increase over 2000 hours, whereas Li-CNF fails before 200 hours. When paired with layered oxide cathodes (NaNi0.33Fe0.3Mn0.33Ti0.04O2 and LiNi0.6Mn0.2Co0.2O2 for sodium and lithium cells, respectively) and cycled at 1C, the Na-CNF cells maintain 75% capacity retention after 500 cycles, but the Li-CNF cells fail shortly after 140 cycles. The primary factor enabling stable long-term cycling for Na-CNF cells is that Na ion undergoes reversible ion intercalation, whereas Li ion is limited to surface adsorption. The inherent carbon crystallinity is found to govern the interaction between the carbon host and alkali metals and is a primary factor in the sustainability and performance of the metal composite anodes.

Charge heterogeneity is a prevalent feature in many electrochemical systems. In a commercial cathode of Li-ion batteries, the composite is hierarchically structured across multiple length scales including the sub-micron single-crystal primary-particle domains up to the macroscopic particle ensembles. The redox kinetics of charge transfer and mass transport strongly couples with mechanical stresses. This interplay catalyzes substantial heterogeneity in the charge (re)distribution, stresses, and mechanical damage in the composite electrode during charging and discharging. We assess the heterogeneous electrochemistry and mechanics in a LiNixMnyCozO2 (NMC) cathode using a fully coupled electro-chemo-mechanics model at the cell level. A microstructure-resolved model is constructed based on the synchrotron X-ray tomography data. We calculate the stress field in the composite and then quantitatively evaluate the kinetics of surface charge transfer and Li transport biased by mechanical stresses. We further model the cyclic behavior of the cell. The repetitive deformation of the active particles and the weakening of the interfacial strength cause gradual increase of the interfacial debonding. The mechanical damage impedes electron transfer, incurs more charge heterogeneity, and results in the capacity degradation in batteries over cycles.

Charge heterogeneity is a prevalent feature in many electrochemical systems. In a commercial cathode of Li-ion batteries, the composite is hierarchically structured across multiple length scales including the sub-micron single-crystal primary-particle domains up to the macroscopic particle ensembles. The redox kinetics of charge transfer and mass transport strongly couples with mechanical stresses. This interplay catalyzes substantial heterogeneity in the charge (re)distribution, stresses, and mechanical damage in the composite electrode during charging and discharging. We assess the heterogeneous electrochemistry and mechanics in a LiNixMnyCozO2 (NMC) cathode using a fully coupled electro-chemo-mechanics model at the cell level. A microstructure-resolved model is constructed based on the synchrotron X-ray tomography data. We calculate the stress field in the composite and then quantitatively evaluate the kinetics of surface charge transfer and Li transport biased by mechanical stresses. We further model the cyclic behavior of the cell. The repetitive deformation of the active particles and the weakening of the interfacial strength cause gradual increase of the interfacial debonding. The mechanical damage impedes electron transfer, incurs more charge heterogeneity, and results in the capacity degradation in batteries over cycles.