Stable Solvent-Derived Inorganic-Rich Solid Electrolyte Interphase (SEI) for High-Voltage Lithium-Metal Batteries

Low-Concentration Electrolyte Engineering for Rechargeable Batteries

Low-concentration electrolytes (LCEs) present significant potential for actual applications because of their cost-effectiveness, low viscosity, reduced side reactions, and wide-temperature electrochemical stability. However, current electrolyte research predominantly focuses on regulation strategies for conventional 1 m electrolytes, high-concentration electrolytes, and localized high-concentration electrolytes, leaving design principles, optimization methods, and prospects of LCEs inadequately summarized. LCEs face unique challenges that cannot be addressed by the existing theories and approaches applicable to the three common electrolytes mentioned above; thus, tailored strategies to provide development guidance are urgently needed. Herein, a systematic overview of recent progress in LCEs is provided and subsequent development directions are suggested. This review proposes the core challenge of the high solvent ratio in LCEs, which triggers unstable organic-enriched electrolyte/electrode interface formation and anion depletion near the anode. On the basis of these issues, modification strategies for LCEs, including passivation interface construction and solvent‒anion interaction optimization, are used in various rechargeable battery systems. Finally, the role of advanced simulations and cutting-edge characterization techniques in revealing LCE failure mechanisms is further highlighted, offering new perspectives for their future development and practical application in next-generation rechargeable batteries.

Self-Regulatory Lean-Electrolyte Flow for Building 600 Wh Kg-1-Level Rechargeable Lithium Batteries

Reducing excess electrolytes offers a promising approach to improve the specific energy of electrochemical energy storage devices. However, using lean electrolytes presents a significant challenge for porous electrode materials due to heterogeneous wetting. The spontaneous wetting of nano- or meso-pores within particles, though seldom discussed, adversely affects wetting under lean electrolyte conditions. Herein, this undesired wetting behavior is mitigated by enlarging the pore-throat ratio, enabling Li-rich layered oxide to function effectively at very low electrolyte/capacity (E/C) ratio of 1.4 g Ah-1. The resulting pouch cell achieves 606 Wh kg-1 and retains 80% capacity (75% energy) after 70 cycles. Through imaging techniques and molecular dynamics simulations, it is demonstrated that the pore-throat ratio effectively determines the permeability of electrolyte within particles. By elucidating pore-relating mechanisms, this work unveils promising potential of manipulating pore structures in porous electrode materials, an approach that can be applied to improve the specific energy of other devices including semi-solid-state lithium batteries.

Revitalizing Lithium Metal Batteries: Strategies for Tackling Dead Lithium Formation and Reactivation

Lithium (Li) metal batteries (LMBs) are among the most promising candidates for future battery technology due to their high theoretical capacity and energy density. However, the formation of dendritic Li, characterized by needle-like structures, poses serious safety issues. To address this, numerous methods are developed to prevent Li dendrite formation. Another significant challenge in LMBs is the formation of inactive Li, known as dead Li, which significantly impacts their Coulombic efficiency and overall performance. This review explores the issues surrounding dead Li in LMBs, specifically focusing on electrically isolated Li metal and the repeatedly generated solid electrolyte interphase (SEI). Advanced techniques for characterizing inactive Li are discussed, alongside various strategies designed to activate or suppress dead Li, thus restoring battery capacity. The review summarizes recent advancements in research related to the activation, reuse, and prevention of dead Li, offering valuable insights for enhancing the efficiency and safety of LMBs. This comprehensive overview provides fundamental guidance for the practical application of Li metal anodes and similar metal batteries.

Effect of the Formation Rate on the Stability of Anode-Free Lithium Metal Batteries

Anode-free Li-ion batteries (AFBs), where a Cu current collector is used to plate and strip Li instead of a classic anode, are promising technologies to increase the energy density of batteries. In addition, AFBs are safer and easier to manufacture than competing Li-metal anodes and solid-state batteries. However, the loss of Li inventory that occurs during the operation of AFBs limits their lifespan and practical application. In this study, we find that, in particular, the current density used during the formation of AFBs has a considerable impact on the cycling stability of the cell. We optimize the formation protocol based on experimental and computational observations of thresholds associated with morphological changes in the plated Li and the chemical composition of the solid-electrolyte interphase. Unlike graphite anodes, which require slow formation cycles, AFBs exhibit improved cycling behavior when formed at the highest current densities that avoid dendritic Li formation. We verify that this strategy for optimizing the formation current density is effective for three different electrolyte formulations and, therefore, provides a straightforward universal rationale to optimize the formation protocols for AFBs.

Electrolyte-Enabled High-Voltage Operation of a Low-Nickel, Low-Cobalt Layered Oxide Cathode for High Energy Density Lithium-Ion Batteries

The lithium-ion battery industry acknowledges the need to reduce expensive metals, such as cobalt and nickel, due to supply chain challenges. However, doing so can drastically reduce the overall battery energy density, attenuating the driving range for electric vehicles. Cycling to higher voltages can increase the capacity and energy density but will consequently exacerbate cell degradation due to the instability at high voltages. Herein, an advanced localized high-concentration electrolyte (LHCE) is utilized to enable long-term cycling of a low-Ni, low-Co layered oxide cathode LiNi0.60Mn0.31Co0.07Al0.02O2 (NMCA) in full cells with graphite or graphite-silicon anodes at 4.5 V (≈4.6 vs Li+/Li). NMCA cells with the LHCE deliver a high initial capacity of 194 mA h g-1 at C/10 rate along with 73% capacity retention after 400 cycles compared to 49% retention in a baseline carbonate electrolyte. This is facilitated by reduced impedance growth, active material loss, and gas evolution with the NMCA cathode. These improvements are attributed to the formation of robust, inorganic-rich interphase layers on both the cathode and anode throughout cycling, which are induced by a favorable salt decomposition in the LHCE. This study demonstrates the efficacy of electrolytes toward facilitating the operation of high-energy-density, long-life, and cost-effective cathodes.

The Interaction in Electrolyte Additives Accelerates Ion Transport to Achieve High-Energy Non-Aqueous Lithium Metal Batteries

Electrolyte engineering is a feasible strategy to realize high energy density lithium metal batteries. However, stabilizing both lithium metal anodes and nickel-rich layered cathodes is extremely challenging. To break through this bottleneck, a dual-additives electrolyte containing fluoroethylene carbonate (10 vol.%) and 1-methoxy-2-propylamine (1 vol.%) in conventional LiPF6 -containing carbonate-based electrolyte is reported. The two additives can polymerize and thus generate dense and uniform LiF and Li3 N-containing interphases on both electrodes' surfaces. Such robust ionic conductive interphases not only prevent lithium dendrite formation in lithium metal anode but also suppress stress-corrosion cracking and phase transformation in nickel-rich layered cathode. The advanced electrolyte enables Li||LiNi0.8 Co0.1 Mn0.1 O2 stably cycle for 80 cycles at 60 mA g-1 with a specific discharge capacity retention of 91.2% under harsh conditions.

A low-concentration all-fluorinated electrolyte for stable lithium metal batteries

A novel low-concentration all-fluorinated electrolyte was designed to stabilize lithium metal batteries with excellent wettability and safety.