Room‐Temperature Liquid Na–K Anode Membranes

Abstract

The Na-K alloy is al iquid at 25 8 8Co veralarge compositional range.The liquid alloyisalso immiscible in the organic-liquid electrolytes of an alkali-ion rechargeable battery,p roviding dendrite-free liquid alkali-metal batteries with al iquid-liquid anode-electrolyte interface at room temperature.T he two liquids are each immobilized in ap orous matrix. In previous work, the porous matrix used to immobilize the alloy was ac arbon paper that is wet by the alloya t 420 8 8C; thea lloyr emains in the paper at room temperature.Here we report aroom-temperature vacuum infiltration of the alloyi nto ap orous Cu or Al membrane and ar eversible stripping/plating of the liquid alloyw ith the immobilized organic-liquid electrolyte;n os elf-diacharge is observed since the liquid Na-K does not dissolve into the liquid carbonate electrolytes.The preparation and stripping/plating of the liquid alkali-metal anode can both now be done safely at room temperature.The electrodes of arechargeable cell change volume during ac harge-discharge cycle; [1] retention of ag ood electrodeelectrolyte interface contact occurs at asolid-liquid interface. Conventional batteries use solid electrodes and al iquid electrolyte, [2] but in 1967, Kummer and Weber showed it is possible to use am olten electrode with as olid electrolyte. [3] Dendrites do not form on al iquid, so am olten alkali-metal electrode solves the safety problem of an alkali-metal battery resulting from anode dendrite formation and growth on plating as olid alkali-metal anode. [4] However,t he solid electrolyte of the Kummer-Weber cell such as the commercialized Na-S battery requires an operating temperature T op > 300 8 8C, which introduces costly maintenance and operation. [3,5] Other cells with molten liquid-metal electrodes suffer from similar problems. [6] ANa-K alloy is liquid at 25 8 8Cover alarge compositional range,a nd recent experiments have shown that this liquid is immiscible with the organic liquid electrolyte of the alkali-ion batteries,t hus allowing dendrite-free liquid alkali-metal batteries with a T op = 25 8 8C. [7][8][9] However,a tr oom temperature,t he liquid Na-K alloy has av ery high surface tension, which prevents it from spreading out over the liquid electrolyte surface.Inorder to wet each other,the liquid Na-K alloy has to be immobilized into ap orous matrix membrane. Initially we used ac arbon paper that soaked up the Na-K liquid only at aw etting temperature of 420 8 8C. [7,8] Although the liquid Na-K alloy remained immobilized in the carbon paper at ambient temperature,w hich allowed its use with al iquid electrolyte and an insertion-compound cathode,t he high temperature infiltration of the highly reactive alkalialloy into the carbon paper is neither economical nor convenient for research and commercialization. [9] Therefore, we report here that the liquid Na-K alloy can be vacuum infiltrated into many metal foams or carbon paper at 25 8 8C.We also show that the resulting electrode membranes are stable on contact with the organic liquid carbonate...

A Novel Sodium–Potassium Anode Supported by Fluorinated Aluminum Foam

“…Additionally, a small amount of liquid sodium-potassium metal escapes to the electrode surface, forming spherical droplets on the NaKC-FAF electrode (the inserted picture of Figure 1f). A similar phenomenon has been described in the literature [13], which speculates that the slight dissolution of the Na-K in ethers may destroy the physical bonding between the liquid Na-K and the porous material. The NaKC-FAF electrode was found to be more structurally stable in the carbonate-based electrolyte (1.0 M NaClO 4 /EC-PC-5% FEC), and thus, this electrolyte was used throughout subsequent experiments.…”

Building Stable Anodes for High‐Rate Na‐Metal Batteries

“…According to the phase diagram of the Na‐K alloy system in Figure A, the liquid state of the Na‐K alloy can be maintained with a Na mass fraction between 9.2–58.2 wt.% at room temperature. [ 255 ] Due to the liquid nature at room temperature, the Na‐K alloy could offer a series of advantages over conventional Na metal anodes, including the robust self‐healing capability to eliminate the dendrite formation, and the enhanced stability of the Na‐metal‐electrolyte interface. [ 256 ] This part focuses on developing the Na‐K alloy as the liquid metal anode for high‐rate SMAs.…”

“…Currently, there are mainly four approaches [258] to enhance the wettability of the Na-K liquid on a carbon substrate: the vacuum infiltration, [255] increasing the contact temperature, [262] introduction of in situ self-assembled SEI layers to form a stable structure, [265] and making use of the capillary effect. [263] For example, Xue et al [255] prepared a uniform Na-K percolating network within a porous Al/Cu substrate using vacuum infiltration. Gu and colleagues [262] improved the wettability of carbon fiber significantly by annealing at 750 °C in Ar atmosphere, followed by dropping some Na-K liquid onto the annealed carbon fiber disk using a pipette.…”

“…[ 263 ] For example, Xue et al. [ 255 ] prepared a uniform Na‐K percolating network within a porous Al/Cu substrate using vacuum infiltration. Gu and colleagues [ 262 ] improved the wettability of carbon fiber significantly by annealing at 750 °C in Ar atmosphere, followed by dropping some Na‐K liquid onto the annealed carbon fiber disk using a pipette.…”

Non‐Newtonian Fluid State K–Na Alloy for a Stretchable Energy Storage Device

“…Sodium–potassium alloy (KNA) combines both of liquid (low viscosity) and metal (high electronic conductivity) properties in a wide temperature range (room‐temperature and even −12.6 °C) . The KNA with liquid phase can be defined as a promising way to solve the safety problem resulting from dendrite formation and growth of alkali metal anode . Nevertheless, due to the high surface tension, flowable liquid KNA cannot be directly used to shape the electrode of alkali metal batteries.…”