A Stable Polymer‐based Solid‐State Lithium Metal Battery and its Interfacial Characteristics Revealed by Cryogenic Transmission Electron Microscopy

Abstract

Solid‐state lithium metal batteries (SSLMBs) are a promising candidate for next‐generation energy storage systems due to their intrinsic safety and high energy density. However, they still suffer from poor interfacial stability, which can incur high interfacial resistance and insufficient cycle lifespan. Herein, a novel poly(vinylidene fluoride‑hexafuoropropylene)‐based polymer electrolyte (PPE) with LiBF4 and propylene carbonate plasticizer is developed, which has a high room‐temperature ionic conductivity up to 1.15 × 10−3 S cm−1 and excellent interfacial stability. Benefitting from the stable interphase, the PPE‐based symmetric cell can operate for over 1000 h. By virtue of cryogenic transmission electron microscopy (Cryo‐TEM) characterization, the high interfacial compatibility between Li metal anode and PPE is revealed. The solid electrolyte interphase is made up of an amorphous outer layer that can keep intimate contact with PPE and an inner Li2O‐dominated layer that can protect Li from continuous side reactions during battery cycling. A LiF‐rich transition layer is also discovered in the region of PPE close to Li metal anode. The feasibility of investigating interphases in polymer‐based solid‐state batteries via Cryo‐TEM techniques is demonstrated, which can be widely employed in future to rationalize the correlation between solid‐state electrolytes and battery performance from ultrafine interfacial structures.

Understanding and controlling lithium morphology in solid polymer and gel polymer systems: mechanisms, strategies, and gaps

“…More ideal, dense, dome-like morphologies have been reported in some of the fluorinated GPEs, 31,61 although not all of them. Other noted morphologies included what was described as ''flaky deposits'' by Lu et al, 64 and ''bush-like'' by He et al 66 To our knowledge, the only globular lithium deposit in a GPE was observed in a single-ion conducting gel electrolyte with a PVDF-HFP host. 67 Thus far, it seems that globular, tree, and bulk deposits have not been noted in gel electrolytes with PEO backbones.…”

“…Fluorination with FEC and LiBF 4 seems to have an advantage over LiPF 6 , as the latter resulted in a mosaic structure rather than the desired multilayer. 64,72,73 However, there is not enough data to draw any conclusions, as only a few studies have investigated the fluorination of GPEs. In a recent study by Lin et al, they examined electrodeposited lithium using a cross-linked PEO-based electrolyte containing a succinonitrile solid plasticizer and FEC additive.…”

“…The lithium morphologies observed in GPEs align with those in liquid electrolytes. Whisker, 31,64 mossy, 33,61,65 dendrite, 33 and spherical deposits 33,38,61,64 are the most commonly reported morphologies. More ideal, dense, dome-like morphologies have been reported in some of the fluorinated GPEs, 31,61 although not all of them.…”

“…Still, only six samples were officially classified as having a layered nanostructure, four of which were liquid, 22,[37][38][39] and two GPEs. 64,73 This, however, makes sense as the mosaic nanostructure is the most common.…”

Composite Solid Electrolyte with Continuous and Fast Organic–Inorganic Ion Transport Highways Created by 3D Crimped Nanofibers@functional Ceramic Nanowires

“…[11,12] As electrolytes based on lithium ion immigration in polymers, solid polymers electrolytes (SPEs) have relatively great advantages when compared to ISEs such as their ease of processing, low cost and excellent contacting with electrodes, which is beneficial to alleviate huge volume expansion of electrodes. [13][14][15] However, most of SPEs are profoundly confined by the disadvantages of low ionic conductivity at room temperature and poor mechanical strength at high temperature, etc. [16][17][18] Simultaneously, the low ion transference number of SPEs (<0.4) may further induce the formation of lithium dendrites.…”