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At least 163 records · Page 9

The Influence of Mesoscale Particle Structure on the Electrode Degradation and Resultant Electrochemistry of Lithium Ion Cells With Nickel Rich Lithium Nickel Manganese Cobalt Oxide Positive Electrodes

Nickel-rich lithium nickel manganese cobalt oxide, NMC (LiNi x Mn y Co z O 2 ), materials are desirable positive electrodes in lithium ion batteries, providing high capacity and energy density. The mesoscale structure of NMC materials is commonly a polycrystalline aggregate, providing opportunity for short lithium ion transport distance of the small primary particles, yet facile material handling due to the larger secondary particles. On (de)lithiation the NMC unit cell changes volume, where the anisotropic strain can result in secondary particle fracture. This secondary particle fracture process during cycling has been associated with several degradation modes of NMC materials in LIBs. In this work, a milling process was determined whereby the secondary particles could be pre-fractured with retention of the parent primary particle crystallographic structure, crystallite size, and morphology, providing the ability to unambiguously determine the influence of NMC secondary particle size and mesostructure on resultant functional behavior. The bulk and interfacial properties and electrochemistry of as-received commercially obtained polycrystal NMC811 (LiNi 0.8 Mn 0.1 Co 0.1 O 2 , PC NMC) and its milled MPC NMC counterpart were compared. The smaller secondary particle size, higher surface area MPC NMC was found to result in 1) greater cathode tortuosity, 2) reduced surface Ni on the cycled MPC cathodes consistent with surface reconstruction, and 3) increased Ni deposition on the anodes from cathode-anode crosstalk. These factors manifested in unfavorable electrochemical behavior of MPC with lower functional capacity at both 1C and C/10 rates and higher impedance over extended moderate voltage (dis)charge cycling.

36 MATERIALS SCIENCE↗

High spatial resolution neutron imaging of lithium-ion batteries: Correlating microstructure and lithium transport

Thick electrodes for lithium-ion batteries can increase the overall energy density, but increasing the electrode thickness introduces charge transport limitations. These limitations may be mitigated through proper electrode structuring. Here, high spatial resolution neutron imaging was used to understand the correlation between microstructure and lithium transport in lithium-ion anodes. Batteries with distinct graphite anode microstructures were produced and studied with high spatial resolution in operando neutron radiography to observe the effects of structure on transport. High spatial resolution neutron computed tomography was performed following in operando neutron radiography. X-ray computed tomography and scanning electron microscopy were used to observe the finer scale anode structure to complement neutron imaging. Solvent-free anodes containing a tightly-packed layered structure confined lithium movement close to the separator. This structure limited capacity, but supported better rate capability. Conversely, a more open pore structure in the wet cast anodes yielded higher capacity with reduced rate capability. Together, these results show that lithium distributions can be controlled by the macroscopic structure of the electrodes, the microstructural pore network, and the microscale active areas that support electrochemical reactions. Furthermore, multimodal imaging applying the complementary strengths of neutron and X-ray methods is shown as a tool for advancing battery design.

25 ENERGY STORAGE↗

Zinc-Doped High-Nickel, Low-Cobalt Layered Oxide Cathodes for High-Energy-Density Lithium-Ion Batteries

High-Ni layered oxides with Ni contents greater than 90% are promising cathode candidates for high-energy-density Li-ion batteries. However, drastic electrode-electrolyte reactions and mechanical degradation issues limit their cycle life and practical viability. We demonstrate here that LiNi 0.94 Co 0.04 Zn 0.02 O 1.99 (NCZ), obtained by incorporating 2 mol% Zn 2+ into an ultrahigh-Ni baseline cathode material LiNi 0.94 Co 0.06 O 2 (NC), delivers superior cell performance. NCZ retains 74% of the initial capacity after 500 cycles in full cell assembled with graphite anode, outperforming NC (62% retention). NCZ also possesses a higher average discharge voltage relative to NC with an outstanding average voltage retention of over 99% after 130 cycles in half cells. Bulk structural investigations unveil that Zn doping promotes a smoother phase transition, suppresses anisotropic lattice distortion, and maintains the mechanical integrity of cathode particles. Furthermore, NCZ shows an enhanced interphase stability after long-term cycling, in contrast to the seriously degraded surface chemistry in NC. Finally, this work provides a practically viable approach for designing higher-energy-density high-Ni layered oxide cathodes for lithium-ion batteries.

25 ENERGY STORAGE↗

Nonpolar Alkanes Modify Lithium‐Ion Solvation for Improved Lithium Deposition and Stripping

Abstract Lithium metal batteries have been plagued by the high reactivity of lithium. Reactive additives that can passivate the lithium metal surface and limit electrolyte accessibility to a fresh lithium surface have been widely explored, but can have limited utility with continuous consumption of the additive. In this work, an alternative strategy is explored. The use of nonreactive cosolvents such as nonpolar alkanes is studied and its is shown that hexane and cyclohexane addition to ether solvents (1,3‐dioxolane and 1,2‐dimethoxyethane) halves the nucleation and growth overpotentials for lithium deposition, increases the cell coulombic efficiency, improves the lithium deposition morphology, increases the electrolyte oxidative stability (>0.2 V), and doubles the cycle life—even when compared to a widely used fluorinated ether. The nonpolar alkanes modify the lithium‐ion solvation environment and reduce the solvation free energy; hence reducing the reaction barrier for lithium deposition. Exploration of nonpolar alkanes as part of the electrolyte mixture is a promising strategy for controlling metal deposition.

Amanchukwu, Chibueze V.↗

Ethylene Carbonate–Free Electrolytes for High–Nickel Layered Oxide Cathodes in Lithium–Ion Batteries

Layered lithium nickel oxide (LiNiO 2 ) can provide very high energy density among intercalation cathode materials for lithium-ion batteries, but suffers from poor cycle life and thermal-abuse tolerance with large lithium utilization. In addition to stabilization of the active cathode material, a concurrent development of electrolyte systems of better compatibility is critical to overcome these limitations for practical applications. Here, with nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC), superior electrochemical and thermal characteristics are obtained with an ultrahigh-nickel cathode (LiNi 0.94 Co 0.06 O 2 ), capable of reaching a 235 mA h g –1 specific capacity. Pouch-type graphite | LiNi 0.94 Co 0.06 O 2 cells in EC-free electrolytes withstand several hundred charge–discharge cycles with minor degradation at both ambient and elevated temperatures. In thermal-abuse tests, the cathode at full charge, while reacting aggressively with EC-based electrolytes below 200 °C, shows suppressed self-heating without EC. Through 3D chemical and structural analyses, the intriguing impact of EC is visualized in aggravating unwanted surface parasitic reactions and irreversible bulk structural degradation of the cathode at high voltages. Finally, these results provide important insights in designing high-energy electrodes for long-lasting and reliable lithium-ion batteries.

25 ENERGY STORAGE↗

Calendar and PHEV Cycle Life Aging of High-Energy, Lithium-Ion Cells Containing Blended Spinel and Layered-Oxide Cathodes

One hundred seven commercially available, off-the-shelf, 1.2-Ah cells were tested for calendar life and CS cycle- and CD cycle-life using the new USABC PHEV Battery Test Manual. Here, the effects of temperature on calendar life, on CS cycle life, and on CD cycle life; the effects of SOC on calendar life and on CS cycle life; and the effects of rest time on CD cycle life were investigated. The results indicated that the test procedures caused performance decline in the cells in an expected manner, calendar < CS cycling < CD cycling. In some cases, the kinetic law changed with test type, from linear-with-time to about t2. Additionally, temperature was found to stress the cells more than SOC, causing increased changes in performance with increasing temperature.

25 ENERGY STORAGE↗

Elevated temperature for life extension of lithium ion power cells

Lithium ion (Li-ion) cells are increasingly being used in high power applications such as Hybrid Electric Vehicles. This paper investigates how the life of lithium ion power cells can be increased by increasing their temperature. End of life (EOL) in power applications is often defined as when the battery is no longer able to provide the required charge/discharge power because the battery voltage exceeds the maximum/minimum allowable voltages associated with the battery's chemistry. Here, this paper shows that battery life can be increased by step-wise temperature increases whenever the battery voltage exceeds a voltage limit when the EOL is reached. Experiments are conducted on commercially available lithium iron phosphate batteries for six months using a charge sustaining HEV cycle. Two, 1 °C temperature increases extend the life of the cells by 2000 cycles (3 months of continuous cycling).

25 ENERGY STORAGE↗

Impact of Ionic Liquid on Lithium Ion Battery with a Solid Poly(Ionic Liquid) Pentablock Terpolymer as Electrolyte and Separator

In this work, a ternary blend solid polymer electrolyte (SPE) consisting of a poly(ionic liquid) (PIL) multiblock polymer, lithium salt, and ionic liquid (IL) was investigated with the goal of understanding the influence of IL concentration on ion transport mechanisms and electrochemical stability. The physical, transport, mechanical, morphological, and electrochemical properties of the ternary blend SPE were systematically investigated as a function of IL concentration (r = [IL]/[PIL] mole ratio between 0.1 and 0.7). The results indicate that with increasing IL concentration, the continuous conductive domain increases along with the polymer chain segmental mobility, as well as facilitate ionic conductivity, while the mechanical modulus exhibits a percolation threshold (from 52.17 MPa to 0.55 MPa at r = 0.2 to 0.3). Surprisingly, at higher IL concentrations, there is a reduction in the lithium cation mobility (i.e., 9.3 × 10-12 m2 s-1 versus 3.8 × 10-12 m2 s-1 for r = 0.2 versus r = 0.5, respectively) as evidenced by pulsed-field gradient nuclear magnetic resonance (PFG-NMR), which coincides with an increased overpotential (i.e., 50 mV versus 150 mV for r = 0.2 versus r = 0.5, respectively) evidenced by lithium metal stripping and plating. This work provides valuable insights into the impact of IL on lithium ion conducting PIL block polymers, which may enable the design of new SPEs with both high ionic conductivity and improved stability for the future lithium ion batteries.

Chen, Tzu-Ling↗

SEI Formation and Lithium-Ion Electrodeposition Dynamics in Lithium Metal Batteries via First-Principles Kinetic Monte Carlo Modeling

The stabilization and enhanced performance of lithium metal batteries (LMBs) depend on the formation and evolution of the Solid Electrolyte Interphase (SEI) layer as a critical component for regulating the Li metal electrodeposition processes. This study employs a first-principles kinetic Monte Carlo (kMC) model to simulate the SEI formation and Li + electrodeposition processes on a lithium metal anode, integrating both the electrochemical electrolyte reduction reactions and the diffusion events giving place to the SEI aggregation processes during battery charge and discharge processes. The model replicates the competitive interactions between organic and inorganic SEI components, emphasizing the influence of the cycling regime. Results indicate that grain boundaries within the SEI facilitate faster lithium-ion transport compared to crystalline regions, crucial for improving the performance and stability of LMBs. The findings underscore the importance of dynamic SEI modeling for further development of next-generation high-energy-density batteries.

25 ENERGY STORAGE↗

Lowering the Activation Barriers for Lithium-Ion Conductivity through Orientational Disorder in the Cyanide Argyrodite Li6PS5CN

Rapid advancements in safe and high-energy-density energy storage are predicated on identifying new solid-state ion conductors with low activation energies and high ionic conductivities for all-solid-state battery technologies. Halide argyrodites are among some of the top candidates for solid-state electrolytes, as they can achieve ionic conductivities that approach liquid electrolytes. Incorporating dynamic pseudohalide species in argyrodite solid electrolytes presents an exciting opportunity to exploit lattice dynamics as a design principle to modulate the ion conduction properties of solid-state ion conductors. In the present study, we have prepared the new argyrodite Li 6 PS 5 CN containing orientationally disordered cyanide ions. The new cyanide argyrodite Li 6 PS 5 CN exhibits an activation barrier to Li-ion transport of 471 ± 25 meV and a room-temperature ionic conductivity of 6(2) × 10 –5 S cm –1 in comparison to the activation barrier of 502 ± 16 meV and an ionic conductivity of 2.3(1) × 10 –4 S cm –1 measured for the bromide analogue Li 6 PS 5 Br. Structural studies of both compounds by high-resolution X-ray diffraction indicate that Li 6 PS 5 CN and Li 6 PS 5 Br adopt nearly identical crystal structures with similar lattice parameters, which indicates that lower activation barriers in Li 6 PS 5 CN arise due to the cyanide ion itself rather than due to changes in the geometry of conduction pathways in the local lithium environment. The orientational disorder of the quadrupolar cyanide ion in Li 6 PS 5 CN points to a complex interplay of lattice polarizability and molecular dynamics that lower the activation barrier for lithium-ion conductivity in the cyanide argyrodite.

25 ENERGY STORAGE↗