Improved capacity retention and ultralong cycle performance of Ni-Fe co-doped LiMn2O4 cathode material at high current densities

Five Volts Lithium Batteries with Advanced Carbonate-Based Electrolytes: A Rational Design via a Trio-Functional Addon Materials

Lithium metal batteries paired with high-voltage LiNi0.5Mn1.5O4 (LNMO) cathodes are a promising energy storage source for achieving enhanced high energy density. Forming durable and robust solid-electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) and the ability to withstand oxidation at high potentials are essential for long-lasting performance. Herein, advanced electrolytes are designed via trio-functional additives to carbonate-based electrolytes for 5 V Li||LNMO and graphite||LNMO cells achieving 88.3% capacity retention after 500 charge-discharge cycles. Theoretical calculations reveal that adding adiponitrile facilitates the presence of more hierarchical DFOB- and PF6 - dual anion structure in the solvation sheath, leading to a faster de-solvation of the Li cation. By combining both fluorine and nitrile additives, an efficient synergistic effect is obtained, generating robust thin inorganic SEI and CEI films, respectively. These films enhance microstructural stability; Li dendrite growth on the Li electrode is being suppressed at the anode side and transition-metals dissolution from the cathode is being mitigated, as evidenced by cryo-transmission electron microscopy and synchrotron studies.

Improving Fast-Charging Capability of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode under Long-Term Cyclability through Co-Doping Strategy

Co-free spinel LiNi0.5Mn1.5O4 (LNMO) is emerging as a promising contender for designing next generation high-energy-density and fast-charging Li-ion batteries, due to its high operating voltage and good Li+ diffusion rate. However, further improvement of the Li+ diffusion ability and simultaneous resolution of Mn dissolution still pose significant challenges for their practical application. To tackle these challenges, a simple co-doping strategy is proposed. Compared to Pure-LNMO, the extended lattice in resulting LNMO-SbF sample provides wider Li+ migration channels, ensuring both enhanced Li+ transport kinetics, and lower energy barrier. Moreover, Sb creating structural pillar and stronger TM─F bond together provides a stabilized spinel structure, which stems from the suppression of detrimental irreversible phase transformation during cycling related to Mn dissolution. Benefiting from the synergistic effect, the LNMO-SbF material exhibits a superior reversible capacity (111.4 mAh g-1 at 5C, and 70.2 mAh g-1 after 450 cycles at 10C) and excellent long-term cycling stability at high current density (69.4% capacity retention at 5C after 1000 cycles). Furthermore, the LNMO-SbF//graphite full cell delivers an exceptional retention rate of 96.9% after 300 cycles, and provides a high energy density at 3C even with a high loading. This work provides valuable insight into the design of fast-charging cathode materials for future high energy density lithium-ion batteries.

Entropy-increased LiMn2O4-based positive electrodes for fast-charging lithium metal batteries

Fast-charging, non-aqueous lithium-based batteries are desired for practical applications. In this regard, LiMn2O4 is considered an appealing positive electrode active material because of its favourable ionic diffusivity due to the presence of three-dimensional Li-ion diffusion channels. However, LiMn2O4 exhibits inadequate rate capabilities and rapid structural degradation at high currents. To circumvent these issues, here we introduce quintuple low-valence cations to increase the entropy of LiMn2O4. As a result, the entropy-increased LiMn2O4-based material, i.e., LiMn1.9Cu0.02Mg0.02Fe0.02Zn0.02Ni0.02O4, when tested in non-aqueous lithium metal coin cell configuration, enable 1000 cell cycles at 1.48 A g-1 (corresponding to a cell charging time of 4 minutes) and 25°C with a discharge capacity retention of about 80%. We demonstrate that the increased entropy in LiMn2O4 leads to an increase in the disordering of dopant cations and a contracted local structure, where the enlarged LiO4 space and enhanced Mn-O covalency improve the Li-ion transport and stabilize the diffusion channels. We also prove that stress caused by cycling at a high cell state of charge is relieved through elastic deformation via a solid-solution transition, thus avoiding structural degradation upon prolonged cycling.