Mesoscopic Phase Transition Kinetics in Secondary Particles of Electrode-Active Materials in Lithium-Ion Batteries

Many compounds used as battery storage electrodes undergo large composition changes during use that are accompanied by a first-order phase transition. Most studies of these phase transitions have focused on the unit cell to single-crystallite scale, whereas real battery electrodes are typically composed of mesoscopic assemblies of nanocrystallites, for which phase transformation mechanisms are poorly understood. In this work, a systematic study is conducted of the potentiostatic (constant driving force) kinetics of phase transition in secondary particles of representative intercalation compounds: LiFePO₄, LiMn_1–<i>x</i>Fe_<i>x</i>PO₄, and Li₄Ti₅O₇. Storage kinetics are studied as a function of overpotential, material composition, primary particle size, and temperature. We find that in regimes where phase transformation occurs, the results can be self-consistently explained as nucleation and growth kinetics within the framework of the Johnson–Mehl–Avrami–Kolmogorov model. This implies that despite the common secondary particle topology, the electrochemically driven phase transformations occur by nucleation and growth with little apparent resistance to phase propagation across the grain boundaries. Growth appears to be one-dimensional in nature, consistent with a hybrid growth model in which rapid surface propagation is followed by slower growth into particles

Mesoscopic Phase Transition Kinetics in Secondary Particles of Electrode-Active Materials in Lithium-Ion Batteries

Many compounds used as battery storage electrodes undergo large composition changes during use that are accompanied by a first-order phase transition. Most studies of these phase transitions have focused on the unit cell to single-crystallite scale, whereas real battery electrodes are typically composed of mesoscopic assemblies of nanocrystallites, for which phase transformation mechanisms are poorly understood. In this work, a systematic study is conducted of the potentiostatic (constant driving force) kinetics of phase transition in secondary particles of representative intercalation compounds: LiFePO₄, LiMn_1–<i>x</i>Fe_<i>x</i>PO₄, and Li₄Ti₅O₇. Storage kinetics are studied as a function of overpotential, material composition, primary particle size, and temperature. We find that in regimes where phase transformation occurs, the results can be self-consistently explained as nucleation and growth kinetics within the framework of the Johnson–Mehl–Avrami–Kolmogorov model. This implies that despite the common secondary particle topology, the electrochemically driven phase transformations occur by nucleation and growth with little apparent resistance to phase propagation across the grain boundaries. Growth appears to be one-dimensional in nature, consistent with a hybrid growth model in which rapid surface propagation is followed by slower growth into particles

Identification of Li-Ion Battery SEI Compounds through ⁷Li and ¹³C Solid-State MAS NMR Spectroscopy and MALDI-TOF Mass Spectrometry

Solid-state ⁷Li and ¹³C MAS NMR spectra of cycled graphitic Li-ion anodes demonstrate SEI compound formation upon lithiation that is followed by changes in the SEI upon delithiation. Solid-state ¹³C DPMAS NMR shows changes in peaks associated with organic solvent compounds (ethylene carbonate and dimethyl carbonate, EC/DMC) upon electrochemical cycling due to the formation of and subsequent changes in the SEI compounds. Solid-state ¹³C NMR spin–lattice (T₁) relaxation time measurements of lithiated Li-ion anodes and reference poly­(ethylene oxide) (PEO) powders, along with MALDI-TOF mass spectrometry results, indicate that large-molecular-weight polymers are formed in the SEI layers of the discharged anodes. MALDI-TOF MS and NMR spectroscopy results additionally indicate that delithiated anodes exhibit a larger number of SEI products than is found in lithiated anodes

In Situ Observation of Random Solid Solution Zone in LiFePO₄ Electrode

Nanostructured LiFePO₄ (LFP) electrodes have attracted great interest in the Li-ion battery field. Recently there have been debates on the presence and role of metastable phases during lithiation/delithiation, originating from the apparent high rate capability of LFP batteries despite poor electronic/ionic conductivities of bulk LFP and FePO₄ (FP) phases. Here we report a potentiostatic in situ transmission electron microscopy (TEM) study of LFP electrode kinetics during delithiation. Using in situ high-resolution TEM, a Li-sublattice disordered solid solution zone (SSZ) is observed to form quickly and reach 10–25 nm × 20–40 nm in size, different from the sharp LFP|FP interface observed under other conditions. This 20 nm scale SSZ is quite stable and persists for hundreds of seconds at room temperature during our experiments. In contrast to the nanoscopically sharp LFP|FP interface, the wider SSZ seen here contains no dislocations, so reduced fatigue and enhanced cycle life can be expected along with enhanced rate capability. Our findings suggest that the disordered SSZ could dominate phase transformation behavior at nonequilibrium condition when high current/voltage is applied; for larger particles, the SSZ could still be important as it provides out-of-equilibrium but atomically wide avenues for Li⁺/e^– transport

Improving the Capacity of Sodium Ion Battery Using a Virus-Templated Nanostructured Composite Cathode

In this work we investigated an energy-efficient biotemplated route to synthesize nanostructured FePO₄ for sodium-based batteries. Self-assembled M13 viruses and single wall carbon nanotubes (SWCNTs) have been used as a template to grow amorphous FePO₄ nanoparticles at room temperature (the active composite is denoted as Bio-FePO₄-CNT) to enhance the electronic conductivity of the active material. Preliminary tests demonstrate a discharge capacity as high as 166 mAh/g at C/10 rate, corresponding to composition Na_0.9FePO₄, which along with higher C-rate tests show this material to have the highest capacity and power performance reported for amorphous FePO₄ electrodes to date

Enhancing the Performance of Viscous Electrode-Based Flow Batteries Using Lubricant-Impregnated Surfaces

Redox flow batteries are a promising technology that can potentially meet the large-scale grid storage needs of renewable power sources. Today, most redox flow batteries are based on aqueous solutions with low cell voltages and low energy densities that lead to significant costs from hardware and balance-of-plant. Nonaqueous electrochemical couples offer higher cell voltages and higher energy densities and can reduce system-level costs but tend toward higher viscosities and can exhibit non-Newtonian rheology that increases the power required to drive flow. This work uses lubricant-impregnated surfaces (LIS) to promote flow in electrochemical systems and outlines their design based on interfacial thermodynamics and electrochemical stability. We demonstrate up to 86% mechanical power savings at low flow rates for LIS compared to conventional surfaces for a lithium polysulfide flow electrode in a half-cell flow battery configuration. The measured specific charge capacity of ∼800 mAh/(g·S) is a 4-fold increase over previous work

Enhancing the Performance of Viscous Electrode-Based Flow Batteries Using Lubricant-Impregnated Surfaces

Redox flow batteries are a promising technology that can potentially meet the large-scale grid storage needs of renewable power sources. Today, most redox flow batteries are based on aqueous solutions with low cell voltages and low energy densities that lead to significant costs from hardware and balance-of-plant. Nonaqueous electrochemical couples offer higher cell voltages and higher energy densities and can reduce system-level costs but tend toward higher viscosities and can exhibit non-Newtonian rheology that increases the power required to drive flow. This work uses lubricant-impregnated surfaces (LIS) to promote flow in electrochemical systems and outlines their design based on interfacial thermodynamics and electrochemical stability. We demonstrate up to 86% mechanical power savings at low flow rates for LIS compared to conventional surfaces for a lithium polysulfide flow electrode in a half-cell flow battery configuration. The measured specific charge capacity of ∼800 mAh/(g·S) is a 4-fold increase over previous work

Enhancing the Performance of Viscous Electrode-Based Flow Batteries Using Lubricant-Impregnated Surfaces

Redox flow batteries are a promising technology that can potentially meet the large-scale grid storage needs of renewable power sources. Today, most redox flow batteries are based on aqueous solutions with low cell voltages and low energy densities that lead to significant costs from hardware and balance-of-plant. Nonaqueous electrochemical couples offer higher cell voltages and higher energy densities and can reduce system-level costs but tend toward higher viscosities and can exhibit non-Newtonian rheology that increases the power required to drive flow. This work uses lubricant-impregnated surfaces (LIS) to promote flow in electrochemical systems and outlines their design based on interfacial thermodynamics and electrochemical stability. We demonstrate up to 86% mechanical power savings at low flow rates for LIS compared to conventional surfaces for a lithium polysulfide flow electrode in a half-cell flow battery configuration. The measured specific charge capacity of ∼800 mAh/(g·S) is a 4-fold increase over previous work

Enhancing the Performance of Viscous Electrode-Based Flow Batteries Using Lubricant-Impregnated Surfaces

Redox flow batteries are a promising technology that can potentially meet the large-scale grid storage needs of renewable power sources. Today, most redox flow batteries are based on aqueous solutions with low cell voltages and low energy densities that lead to significant costs from hardware and balance-of-plant. Nonaqueous electrochemical couples offer higher cell voltages and higher energy densities and can reduce system-level costs but tend toward higher viscosities and can exhibit non-Newtonian rheology that increases the power required to drive flow. This work uses lubricant-impregnated surfaces (LIS) to promote flow in electrochemical systems and outlines their design based on interfacial thermodynamics and electrochemical stability. We demonstrate up to 86% mechanical power savings at low flow rates for LIS compared to conventional surfaces for a lithium polysulfide flow electrode in a half-cell flow battery configuration. The measured specific charge capacity of ∼800 mAh/(g·S) is a 4-fold increase over previous work

Enhancing the Performance of Viscous Electrode-Based Flow Batteries Using Lubricant-Impregnated Surfaces

Redox flow batteries are a promising technology that can potentially meet the large-scale grid storage needs of renewable power sources. Today, most redox flow batteries are based on aqueous solutions with low cell voltages and low energy densities that lead to significant costs from hardware and balance-of-plant. Nonaqueous electrochemical couples offer higher cell voltages and higher energy densities and can reduce system-level costs but tend toward higher viscosities and can exhibit non-Newtonian rheology that increases the power required to drive flow. This work uses lubricant-impregnated surfaces (LIS) to promote flow in electrochemical systems and outlines their design based on interfacial thermodynamics and electrochemical stability. We demonstrate up to 86% mechanical power savings at low flow rates for LIS compared to conventional surfaces for a lithium polysulfide flow electrode in a half-cell flow battery configuration. The measured specific charge capacity of ∼800 mAh/(g·S) is a 4-fold increase over previous work