Rechargeable batteries with lithium metal anodes exhibit higher energy densities than conventional lithium-ion batteries. Solid-state electrolytes (SSEs) provide the opportunity to unlock the full potential of lithium metal anodes and fundamentally eliminate safety concerns caused by flammable liquid electrolytes. Up to now, most studies on SSEs have been focused on enhancing the ionic conductivity and improving the interfacial stability. However, the electrolyte thickness, which has received less attention, also plays an important role in determining the energy density and electrochemical performance of all-solid-state lithium batteries (ASSLBs). Recognizing this, our review evaluates SSE studies beyond traditional factors and focuses on a thickness perspective. We systematically analyze the influence of the electrolyte thickness on the energy densities of ASSLB pouch cells, and highlight the strategies that dramatically reduce the thickness of SSE membranes without sacrificing their mechanical properties. Then, we discuss recent advances and challenges of ASSLBs based on high-voltage and high-capacity cathodes, as well as novel configurations such as bipolar and flexible ASSLBs. Finally, we provide perspectives and suggestions towards high energy-density ASSLBs for future commercialization.

Reducing the thickness of solid-state electrolyte membranes for high-energy lithium batteries

/pdf/emerging-era-of-electrolyte-solvation-structure-and-1lk4417c.pdf

Emerging Era of Electrolyte Solvation Structure and Interfacial Model in Batteries

https://hal.archives-ouvertes.fr/hal-02944545/document

Challenges of today for Na-based batteries of the future: From materials to cell metrics

Critical effects of electrolyte recipes for Li and Na metal batteries

Recent development of lithium argyrodite solid-state electrolytes for solid-state batteries: Synthesis, structure, stability and dynamics

The solid-electrolyte interphase (SEI) is known to dictate the performance of a Li metal anode, where its inorganic compositions are primarily responsible for Li+ conduction, electron insulation, a...

Tailoring Electrolyte Solvation Chemistry toward an Inorganic-Rich Solid-Electrolyte Interphase at a Li Metal Anode

Current knowledge on Na metal anode has been limited on its room-temperature or high-temperature (molten Na-S system) performances. However, the properties related to its low-temperature and fast-charging performances are rarely covered. Herein, we show that, using a conventional carbonate-based electrolyte, needle-like Na deposits sprout at −20 °C with a spiking impedance of ∼2.8 × 104 Ω observed in symmetric cell configuration, making an early failure of the battery within tens of hours. By knocking down the kinetic barriers of Na+ ion de-solvation and its subsequent diffusion through the solid electrolyte interphase (SEI), we enable flat and spherical Na deposits at −20 °C with a massively reduced interfacial impedance. This has been realized by using (i) a weakly solvated electrolyte that shows a low solvation energy towards Na+ ions, and (ii) a Na15Sn4/NaF biphasic artificial SEI for promoting unhindered Na+ ion transfer at the Na metal/electrolyte interface. Ultimately, a high-voltage Na/Na3V2(PO4)2O2F battery is developed to stand low temperatures down to −30 °C and fast charging up to 30C. The design strategy provided herein underlines the simultaneous de-solvation and SEI control for achieving low-temperature and fast-charging sodium metal batteries and presents as a prototype of how the kinetic barriers can be overcome under extreme conditions.

Knocking down the kinetic barriers towards fast-charging and low-temperature sodium metal batteries

Fluoride-Rich Solid-Electrolyte-Interface Enabling Stable Sodium Metal Batteries in High-Safe Electrolytes

The recent revival of Li metal anodes (LMA) leads to a renewed interest in LMA as the ultimate choice for rechargeable lithium batteries towards high energy density. However, multiple challenges stand in the way of using LMA, of which high reactivity, dendrite growth, the difficulty of fabricating Li thin foils, and the flammability of organic liquid electrolytes are typical. Here, a writable Li metal ink (LMI) prepared by introducing biomass-derived carbon particles into molten Li is presented. Due to the significantly decreased surface tension, LMI is able to directly write on copper foils or other substrates that ultrathin Li foils with a remarkably small thickness ( can be achieved. The versatility of LMI is further demonstrated in addressing the interface issue between LMA and garnet-type solid-state electrolytes, where directly writing LMI on the garnet offers a perfect contact and enables an extremely low interfacial resistance of 6 Ω cm2, in sharp contrast to 939 Ω cm2 between the pure Li and the garnet. Due to the successful partnership with non-flammable solid-state electrolytes, ink-based technology may have a chance to bring us very close to the use of solid-state lithium metal batteries (SSLMBs) with high safety and high energy density.

A writable lithium metal ink

Sodium metal anodes (SMAs) suffer from extremely low reversibility (<20%) in carbonate-based electrolytes—this piece of knowledge gained from previous studies has ruled out the application of carbonate solvents for sodium metal batteries. Here, we overturn this conclusion by incorporating fluoroethylene carbonate (FEC) as cosolvent that renders a Na plating/stripping efficiency of >95% with conventional NaPF6 salt at a regular concentration (1.0 M). The peculiar role of FEC is firstly unraveled via its involvement into the solvation structure, where a threshold FEC concentration with a coordination number>1.2 is needed in guaranteeing high Na reversibility over the long-term. Specifically, by incorporating an average number of 1.2 FEC molecules into the primary Na+ solvation sheath, lowest unoccupied molecular orbital (LUMO) levels of such Na+-FEC solvates undergo further decrease, with spin electrons residing either on the O=CO(O) moiety of FEC or sharing between Na+ and its C=O bond, which ensures a prior FEC decomposition in passivating the Na surface against other carbonate molecules. Further, by adopting cryogenic transmission electron microscopy (cryo-TEM), we found that the Na filaments grow into substantially larger diameter from ~400 nm to >1 μm with addition of FEC upon the threshold value. A highly crystalline and much thinner (~40 nm) solid-electrolyte interphase (SEI) is consequently observed to uniformly wrap the Na surface, in contrast to the severely corroded Na as retrieved from the blank electrolyte. The potence of FEC is further demonstrated in a series of “corrosive solvents” such as ethyl acetate (EA), trimethyl phosphate (TMP), and acetonitrile (AN), enabling highly reversible SMAs in the otherwise unusable solvent systems.

https://downloads.spj.sciencemag.org/research/2022/9754612.pdf

Xuyang Liu

Papers

Tailoring Electrolyte Solvation Chemistry toward an Inorganic-Rich Solid-Electrolyte Interphase at a Li Metal Anode

Knocking down the kinetic barriers towards fast-charging and low-temperature sodium metal batteries

Fluoride-Rich Solid-Electrolyte-Interface Enabling Stable Sodium Metal Batteries in High-Safe Electrolytes

A writable lithium metal ink

Deciphering the Role of Fluoroethylene Carbonate towards Highly Reversible Sodium Metal Anodes