RESUMEN
The prominent problem with graphite anodes in practical applications is the detrimental Li plating, resulting in rapid capacity fade and safety hazards. Herein, secondary gas evolution behavior during the Li-plating process was monitored by online electrochemical mass spectrometry (OEMS), and the onset of local microscale Li plating on the graphite anode was precisely/explicitly detected in situ/operando for early safety warnings. The distribution of irreversible capacity loss (e.g., primary and secondary solid electrolyte interface (SEI), dead Li, etc.) under Li-plating conditions was accurately quantified by titration mass spectroscopy (TMS). Based on OEMS/TMS results, the effect of typical VC/FEC additives was recognized at the level of Li plating. The nature of vinylene carbonate (VC)/fluoroethylene carbonate (FEC) additive modification is to enhance the elasticity of primary and secondary SEI by adjusting organic carbonates and/or LiF components, leading to less "dead Li" capacity loss. Though VC-containing electrolyte greatly suppresses the H2/C2H4 (flammable/explosive) evolution during Li plating, more H2 is released from the reductive decomposition of FEC.
RESUMEN
Development of high-energy-density rechargeable battery systems not only needs advanced qualitative characterizations for mechanism exploration but also requires accurate quantification technology to quantitatively elucidate products and fairly assess numerous modification strategies. Herein, as a reliable quantification technology, titration mass spectroscopy (TMS) is developed to accurately quantify O-related anionic redox reactions (Li-O2 battery and nickel-cobalt-manganese (NCM)/Li-rich cathodes), parasitic carbonate deposition and decomposition (derived from air-exposure degradation and electrolyte oxidation), and dead Li0 formation (Li-metal battery and over-discharged graphite anode). TMS technology can harvest key information on products (e.g., quantification of oxidized lattice oxygen and solid electrolyte interphase (SEI)/cathode electrolyte interphase (CEI) components) and guide corresponding design strategy by enhancing understanding of the mechanism (e.g., clearly distinguish the catalytic target of highly oxidative Ni4+ on the NCM cathode). Not limited as a rigid quantification tool for widely known products/mechanisms, TMS technology has been demonstrated as a powerful and versatile tool for the investigations of advanced batteries.
RESUMEN
Raising the charging cut-off voltage of layered oxide cathodes can improve their energy density. However, it inevitably introduces instabilities regarding both bulk structure and surface/interface. Herein, exploiting the unique characteristics of high-valence Nb5+ element, a synchronous surface-to-bulk-modified LiCoO2 featuring Li3 NbO4 surface coating layer, Nb-doped bulk, and the desired concentration gradient architecture through one-step calcination is achieved. Such a multifunctional structure facilitates the construction of high-quality cathode/electrolyte interface, enhances Li+ diffusion, and restrains lattice-O loss, Co migration, and associated layer-to-spinel phase distortion. Therefore, a stable operation of Nb-modified LiCoO2 half-cell is achieved at 4.6 V (90.9% capacity retention after 200 cycles). Long-life 250 Wh kg-1 and 4.7 V-class 550 Wh kg-1 pouch cells assembled with graphite and thin Li anodes are harvested (both beyond 87% after 1600 and 200 cycles). This multifunctional one-step modification strategy establishes a technological paradigm to pave the way for high-energy density and long-life lithium-ion cathode materials.
RESUMEN
Developing sacrificial cathode prelithiation technology to compensate for active lithium loss is vital for improving the energy density of lithium-ion battery full-cells. Li2CO3 owns high theoretical specific capacity, superior air stability, but poor conductivity as an insulator, acting as a promising but challenging prelithiation agent candidate. Herein, extracting a trace amount of Co from LiCoO2 (LCO), a lattice engineering is developed through substituting Li sites with Co and inducing Li defects to obtain a composite structure consisting of (Li0.906Co0.043â«0.051)2CO2.934 and ball milled LiCoO2 (Co-Li2CO3@LCO). Notably, both the bandgap and LiâO bond strength have essentially declined in this structure. Benefiting from the synergistic effect of Li defects and bulk phase catalytic regulation of Co, the potential of Li2CO3 deep decomposition significantly decreases from typical >4.7 to ≈4.25 V versus Li/Li+, presenting >600 mAh g-1 compensation capacity. Impressively, coupling 5 wt% Co-Li2CO3@LCO within NCM-811 cathode, 235 Wh kg-1 pouch-type full-cell is achieved, performing 88% capacity retention after 1000 cycles.
RESUMEN
Aqueous zinc-metal batteries have attracted extensive attention due to their outstanding merits of high safety and low cost. However, the intrinsic thermodynamic instability of zinc in aqueous electrolyte inevitably results in hydrogen evolution, and the consequent generation of OH- at the interface will dramatically exacerbate the formation of dead zinc and dendrites. Herein, a dynamically interfacial pH-buffering strategy implemented by N-methylimidazole (NMI) additive is proposed to remove the detrimental OH- at zinc/electrolyte interface in real-time, thus eliminating the accumulation of by-products fundamentally. Electrochemical quartz crystal microbalance and molecular dynamics simulation results reveal the existence of an interfacial absorption layer assembled by NMI and protonated NMI (NMIH+ ), which acts as an ion pump for replenishing the interface with protons constantly. Moreover, an in situ interfacial pH detection method with micro-sized spatial resolution based on the ultra-microelectrode technology is developed to probe the pH evolution in diffusion layer, confirming the stabilized interfacial chemical environment in NMI-containing electrolyte. Accordingly, with the existence of NMI, an excellent cumulative plating capacity of 4.2 Ah cm-2 and ultrahigh Coulombic efficiency of 99.74% are realized for zinc electrodes. Meanwhile, the NMI/NMIH+ buffer additive can accelerate the dissolution/deposition process of MnO2 /Mn2+ on the cathode, leading to enhanced cycling capacity.