CN111868977A - Composite electrode material for fluoride ion electrochemical cells - Google Patents

Abstract

The present disclosure relates to a method of preparing core-shell and yolk-shell nanoparticles, and electrodes comprising the same. Core-shell and yolk-shell nanoparticles and electrodes comprising them are suitable for use in electrochemical cells such as fluoride ion shuttle cells. The shell can protect the metal core from oxidation, including in electrochemical cells. In some embodiments, the electrochemically active structure includes a variable-sized active material that forms particles that expand or contract when reacted with or release fluoride ions. The one or more particles are at least partially surrounded by the fluoride ion-conducting encapsulant and one or more voids are formed between the active material and the encapsulant, optionally using a sacrificial layer or selective etching. The fluoride ion-conducting encapsulant may comprise one or more metals. When the electrochemically active structure is used in a secondary battery, the presence of the voids can accommodate dimensional changes in the active material.

Description

Composite electrode material for fluoride ion electrochemical cells

Cross Reference to Related Applications

The present application claims priority from us patent application No. 16/013,739 entitled "Barium-material compositions for Fluoride Electrochemical Cells" filed on 20.6.2018, which is a continuation-in-part application from us patent application No. 15/844,079 entitled "composition Electrode Materials for Fluoride-Ion Electrochemical Cells" filed on 15.12.2017, us patent application No. 15/844,079 claims priority from us patent application No. 62/434,611 entitled "composition Electrode Materials for Fluoride-Ion Electrochemical Cells" filed on 15.2016, and us patent application No. 62/453,295 entitled "composition Electrode Materials for Fluoride-Ion Electrochemical Cells" filed on 1.2.2.2017; U.S. patent application No. 16/013,739 also claims priority from U.S. patent application No. 62/676,693 entitled "Composite Electrode Materials for fluorine-Ion Electrochemical Cells" filed on 25/5.2018. This application also claims priority from U.S. patent application No. 62/676,693. Each of the foregoing applications is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to electrochemically active materials, and more particularly to fluoride ion battery systems comprising electrode materials having tailored structures and compositions to improve battery performance. More specifically, the present disclosure relates to core-shell nanoparticles, methods of making the same, and uses thereof in electrochemical cells.

Background

Metal nanoparticles are well suited for use in many applications, including as catalysts and as electrode materials for batteries. However, the use of metal nanoparticles may be limited by system operating conditions or other factors. For example, fluoride ion (fluoride) shuttle batteries are gaining increasing interest as a replacement for lithium ion batteries. However, the materials that can be used in the fluoride ion shuttle battery system are limited, in part because operating conditions are detrimental to many materials that may otherwise be included in the fluoride ion shuttle battery electrodes.

A fluoride ion battery is an electrochemical cell that operates by a fluoride ion-mediated electrode reaction (i.e., the containment or release of fluoride ions at the electrode upon charging or discharging, typically by a conversion type reaction). Such electrochemical cells may provide greater energy density, lower cost, and/or improved safety characteristics compared to lithium and lithium ion batteries. Fluoride ion systems have been validated in the solid state, for example, in US 7,722,993 to potain, which describes An embodiment of a secondary electrochemical cell wherein fluoride ions are reversibly exchanged between an anode and a cathode during charge-discharge cycles, the electrodes being in contact with a solid fluoride ion-conducting electrolyte. Potanin describes the use of alloying additives such as one or more alkaline earth metal fluorides (CaF)₂、SrF₂、BaF₂) And/or alkali metal fluorides (LiF, KF, NaF) and/or alkali metal chlorides (LiCl, KCl, NaCl), and a wide range of other complex fluorides together contain fluorides of La, Ce or complex fluorides based thereon. However, such electrochemical cells only operate efficiently above room temperature (e.g., 150 ℃) due to the limited conductivity of the solid electrolyte.

Attempts have also been made to provide fluoride ion based electrochemical systems that are capable of using liquid electrolytes. For example, U.S. Pat. Nos. 2011-0143219A 1 to Weiss et al and U.S. Pat. No. 9,166,249 to Darolles et al disclose configurations of fluoride ion batteries that employ solvent-based fluoride salts that are at least partially present in solution in the electrolyte. However, for many applications, the chemical reactivity of the electrode material with liquid electrolytes is significant, and these liquid electrolyte systems do not provide sufficiently reliable high discharge and/or high capacity operation.

Disclosure of Invention

The following presents a simplified summary of one or more aspects of the disclosure in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In some embodiments, the present disclosure relates to an electrochemically active structure comprising: a core comprising an active material; and a fluoride-containing shell at least partially surrounding the active material, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is barium.

In some embodiments, the present disclosure relates to a method of making a coated metal nanoparticle, the method comprising: a) providing a water/metal nanoparticle mixture; b) exposing the water/metal nanoparticle mixture to an inert atmosphere; and c) forming a fluoride-containing shell around the metal nanoparticle core, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is barium.

In some embodiments, the present disclosure relates to an electrode comprising: a core comprising copper nanoparticles; and, a fluoride-containing shell at least partially surrounding the copper nanoparticles, wherein the fluoride-containing shell comprises barium and lanthanum in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride-containing shell is 1.

In some embodiments, the present disclosure relates to an electrochemically active structure comprising: a core comprising an active material; and a fluoride-containing shell at least partially surrounding the active material, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is a divalent or tetravalent metal cation.

These and other aspects of the invention will be more fully understood upon reading the following detailed description.

Drawings

Fig. 1A illustrates a cross-section of a core-shell nanoparticle of one aspect of the present disclosure, the core-shell nanoparticle comprising a core comprising a metal nanoparticle and a shell comprising a metal halide or metal oxyhalide.

Figure 1B outlines the general approach to obtain "yolk-shell" complexes using a sacrificial inorganic "middle" layer.

Figure 1C depicts the approach of obtaining a "yolk-shell" complex using a "middle" layer of sacrificial polymer.

Fig. 1D depicts an alternative approach to obtain a "yolk-shell" complex in the absence of a sacrificial "middle" layer.

Figure 1E depicts a variation of the "sacrificial" synthesis of the "yolk-shell" complex, in which nanoparticles of active material are grown on the surface of the "sacrificial" material.

FIG. 1F summarizes the growth of active material in the internal structure or pores of a preformed "sacrificial" material.

Fig. 1G summarizes the growth of active materials in the internal structure or pores of a preformed "sacrificial" material, where the shell constituent components are selected to be electrochemically inert at the electrochemical reaction potentials of interest.

Fig. 2 is a schematic diagram of a fluoride ion electrochemical cell in accordance with an aspect of the present disclosure.

Fig. 3 shows an XRD pattern of the isolated copper nanoparticles of comparative example 1 without shell immediately after synthesis and isolation ("as-made").

Fig. 4 shows stacked XRD patterns of the isolated copper nanoparticles of comparative example 1 without a shell in the as-prepared state and after exposure to air for 4 days and 9 days.

FIG. 5 shows the Cu-LaF of Experimental example 1 in the as-synthesized state, one aspect of the disclosure ₃XRD pattern of core-shell nanoparticles.

FIG. 6 shows Cu-LaF of Experimental example 1₃Stacked XRD patterns of core-shell nanoparticles after 9, 16 and 23 days of exposure to air.

FIGS. 7A and 7B are Cu-LaF of Experimental example 1₃Transmission Electron Microscope (TEM) images of core-shell nanoparticles in the as-fabricated state.

FIG. 8A shows Cu-LaF of Experimental example 1₃High resolution TEM images of core-shell nanoparticles, indicating Cu (core) and LaF₃(shell) region. Fig. 8B and 8C show magnified images of the same nanoparticles.

FIG. 9 is a Cu-LaF including Experimental example 1 in one aspect of the disclosure₃Schematic of a fluoride ion electrochemical cell with core-shell nanoparticles as the active material in the negative electrode (anode).

FIG. 10A is a Cu-LaF including Experimental example 1 in one aspect of the disclosure₃Voltage-specific capacity plots for electrochemical testing of half-cell batteries with core-shell nanoparticles as the active material in the electrode.

Fig. 10B is an X-ray diffraction spectrum of the electrode tested for the half cell battery of fig. 10A measured under initial conditions, after discharge, and after charge.

Fig. 11 shows an XRD pattern of the nanoparticles of comparative example 2 in a synthesized state.

Fig. 12 shows stacked XRD patterns of the nanoparticles of comparative example 2 after 8, 15 and 22 days of exposure to air.

FIG. 13 is a TEM image of nanoparticles of comparative example 2, shown with LaF₃Of copper nanoparticles and LaF not associated with copper nanoparticles₃。

FIG. 14 shows LaF₃the/Cu and Cu film configurations and cyclic voltammetry data.

FIG. 15A shows LaF₃Cyclic voltammograms of/Cu bilayer films. Fig. 15B and 15C show X-ray photoelectron spectroscopy (XPS) data of C, La, O, F and Cu at various etching time lengths at voltages 1 and 2 shown in fig. 15A.

FIG. 16 illustrates a Cu @ LaF according to some aspects of the present disclosure₃And Cu @ Ba_xLa_1-xF_3-xSchematic representation of nanoparticles.

FIG. 17A illustrates Cu @ La according to some aspects of the present disclosure_0.97Ba_0.03F_2.97Examples of Scanning Electron Microscope (SEM) images of (a).

17B-C illustrate Cu @ La according to some aspects of the present disclosure_0.97Ba_0.03F_2.97An example of a Transmission Electron Microscope (TEM) image of (a).

FIG. 17D illustrates Cu @ La according to some aspects of the present disclosure_0.97Ba_0.03F_2.97An example of an energy dispersive X-ray (EDX) image of (a). FIGS. 17E-H show component Cu, F, La, and Ba image maps, respectively.

FIGS. 18A-D illustrate Cu @ La according to aspects of the present disclosure_0.97Ba_0.03F_2.97X-ray photoelectron spectroscopy (XPS) spectrum.

FIG. 19 illustrates a schematic representation of a system according to some aspects of the present disclosure Cu@LaF₃And Cu @ La_0.97Ba_0.03F_2.97XRD pattern of (a).

FIG. 20A illustrates associating Ag/Ag according to aspects of the present disclosure⁺Reference electrode to Cu @ LaF₃Electrodes or Cu @ Ba_xLa_1-xF_3-xVoltage curve of the first charge-discharge cycle of the electrode.

Fig. 20B illustrates a Cu @ LaF according to some aspects of the present disclosure₃And Cu @ La_0.97Ba_0.03F_2.97Comparison of the achieved capacities.

FIG. 20C illustrates Cu @ La according to some aspects of the present disclosure_0.97Ba_0.03F_2.97And XRD patterns after the first charge and the subsequent first discharge.

FIG. 20D illustrates a Cu @ LaF according to some aspects of the present disclosure₃And XRD patterns after the first charge and the subsequent first discharge.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. It will be apparent, however, to one skilled in the art that these concepts may be practiced without these specific details. In some instances, well known components are shown in block diagram form in order to avoid obscuring such concepts.

In general, the present disclosure relates to electrochemically active materials and fluoride ion battery systems including electrode materials having tailored structures and compositions to improve battery performance. In some aspects, the present disclosure relates to core-shell nanoparticles, devices incorporating the core-shell nanoparticles, and methods of making and using the core-shell nanoparticles and devices comprising the core-shell nanoparticles.

Primary and secondary electrochemical cells, such as batteries, utilizing fluoride ion charge carriers, active electrode materials and suitable liquid electrolytesConventional prior art lithium and lithium ion battery alternatives can be provided. Such fluoride ion cell (FIB) systems can operate efficiently at room temperature while utilizing fluoride anions carried in the liquid electrolyte as at least some of the charge carriers in the electrochemical cell. The FIB system has an anode and a cathode that are physically separated from each other but in common contact with a fluorine ion conducting electrolyte. The anode is typically a low potential element or compound and may be a metal, metal fluoride or intercalation composition. Similarly, the cathode may be an element or composition, and may be a metal, metal fluoride, or intercalation composition, which has a higher potential than the anode. Fluorine ion (F) in fluorine ion conducting electrolyte ^-) From cathode to anode during discharge of the battery and from anode to cathode during charge of the battery:

discharging:

anode: MF (MF)_x+nF-→MF_x+n+ ne- (fluoride ion holding, oxidation)

Cathode: MF (MF)_y+ne-→MF_y-n+ nF- (fluoride ion release, reduction)

During charging, the reverse reaction occurs.

For example, a FIB cell reaction based on fluoride anion transfer between Ca and Cu (both metals are capable of forming metal fluorides) may be:

discharging:

Ca+CuF₂→CaF₂+Cu

charging:

CaF₂+Cu→Ca+CuF₂

two challenges exist to achieve stable, reliable long-term cycling of FIB electrodes. First, the reversibility of the electrochemical reactions described above is observed when the metal or metal fluoride active material is nano-sized (i.e., at least one particle size dimension is less than 1 μm). However, particles with such small dimensions have high surface energies and often are associated with electrolyte components (e.g., F)^-) Are reactive and give undesirable side reactions, including "self-discharge" (i.e., chemical reactions such as M + nF)^-→MF_nIt produces no current). It is desirable to form the coating, shell,Layers, etc. to encapsulate the active material particles while still allowing F to be present when desired (i.e., during electrochemical charging or discharging)^-The ions pass through. The encapsulating material may also protect the active material from such side reactions, thereby achieving long-term cycling stability of these electrode materials.

Secondly, such electrochemical reactions are conversion processes in which the structure of the metal or metal fluoride is decomposed in the electrochemical process and reformed into the metal fluoride or metal, respectively, in the process. This conversion process results in a significant volume change between the charged and discharged states of the active material, as shown by the examples given in table 1 below:

table 1: volume change of metal to metal fluoride conversion

This significant volume change can limit the usefulness of a conformal protective coating that encapsulates the particles of FIB electrode material because one particular charge state does not necessarily conform to particles in a different charge state due to the volume change. What is needed are compositions and methods that protect electrode active materials from side reactions with the electrolyte, allow ionic conduction through the encapsulant, and have sufficient void space within the encapsulant and/or encapsulant expansion/contraction properties to accommodate volume changes of the active material during charge and discharge without allowing direct contact between the active material and the electrolyte. In some embodiments, sufficient void space may be void-free space. Such compositions and their preparation will be outlined below.

As used herein, the term "about" is defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the term "about" is defined as within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

In some embodiments, as shown in fig. 1A, a core-shell nanoparticle includes a core comprising a metal or metal alloy ("Me") and a shell comprising a metal halide or metal oxyhalide. The metal of the core may be the same as the metal of the metal halide shell. In some embodiments, the metal of the core and the metal of the metal halide or metal oxyhalide shell are different metals. In some embodiments, the metal halide shell may itself comprise two metals. The core-shell nanoparticles of the present disclosure may be incorporated into a variety of methods and applications, including but not limited to electrodes for use in electrochemical cells, including fluoride ion shuttle cells as shown in fig. 2.

Metals or metal alloys used to form the core include, but are not limited to, iron nanoparticles, cobalt nanoparticles, nickel nanoparticles, copper nanoparticles, lead nanoparticles, and alkaline earth metal nanoparticles. In a preferred embodiment, the metal nanoparticles are selected from cobalt nanoparticles and copper nanoparticles. In another preferred embodiment, the metal nanoparticles are copper nanoparticles. The metal used to form the core may be synthesized by mixing a metal precursor solution with a reducing agent to form metal nanoparticles.

In some embodiments, the metal nanoparticles used to form the core may be synthesized in the presence of a stabilizer that will prevent or otherwise inhibit oxidation of the metal nanoparticles during synthesis and may be readily removed from the metal nanoparticles prior to formation of a metal halide or metal oxyhalide shell thereon. For example, a bulk polymer such as polyvinylpyrrolidone (molecular weight of 55,000g/mol) used during synthesis of metal nanoparticles will inhibit oxidation of the metal nanoparticles. However, such stabilizers are not easily removed from the metal nanoparticles after synthesis. Without being bound by any particular theory, residual stabilizer may form an additional layer between the core formed by the metal nanoparticles and the metal halide or oxyhalide shell, which detracts from the performance of the core-shell nanoparticles in the desired system. For example, in F-shuttle cells it is desirable to maintain the conductivity of the core-shell nanoparticles used as electrode materials. However, a core-shell material comprising an additional layer of residual stabilizer between the core and the shell would likely result in increased space between the electrode materials; the additional residual stabilizer layer and/or the resulting increased space may reduce the electrical conductivity of the core-shell material. Without wishing to be bound by any particular theory, the additional stabilizer layer may hinder fluoride ion-conducting contact between the core and the shell, while the absence of the stabilizer may increase the likelihood of fluoride ion conduction from the core to the shell.

Thus, stabilizers may be used in the synthesis of metal nanoparticles used to form the core, which may be easily removed from the core prior to forming the metal halide or metal oxyhalide shell directly on the core to minimize the amount of stabilizer on the surface of the core. In one non-limiting example, one or more stabilizers that can be used in the synthesis of the metal nanoparticles have a molecular weight (alone or weight-average) of less than 1000g/mol, optionally less than 500g/mol, optionally less than 375g/mol, optionally less than 350 g/mol. Illustrative examples include cetyltrimethylammonium bromide (CTAB) with a molecular weight of 364g/mol, citric acid with a molecular weight of 192g/mol and mixtures thereof.

In some embodiments, the shell of the core-shell nanoparticles may be formed by mixing the isolated metal nanoparticles used to form the core with, for example, a metal salt solution and a halide (halide) salt solution, which react to form a metal halide shell on the core. The shell is deposited directly on the metal core and may completely surround the core, as shown in fig. 1A. In some embodiments, the metal salt used to form the shell is selected from the group consisting of alkali metal salts, alkaline earth metal salts, and transition metal salts. In certain embodiments, the metal salt used to form the shell is a transition metal salt. In certain embodiments, the metal salt used to form the shell is selected from the group consisting of lanthanum, cerium, and magnesium salts. In certain embodiments, the metal salt used to form the shell is selected from lanthanum salts and cerium salts. In certain embodiments, the metal salt is a lanthanum salt. In a preferred embodiment, the lanthanum salt is lanthanum nitrate. In some embodiments, the halide ion salt is sodium fluoride. In one non-limiting example, the shell comprises a metal fluoride or metal oxyfluoride-containing material (i.e., CeF) ₃、CeOF、LaOF、LaF₃)。

In some embodiments, the metal salt solution comprises two metal salts. In some such embodiments, one of the two metal salts is a barium salt. In some embodiments, the metal salt solution comprises a barium salt and a lanthanum salt. In some embodiments, the metal salt solution comprises barium nitrate and lanthanum nitrate. In some embodiments, the metal salt solution comprises barium nitrate and lanthanum nitrate in a ratio of about 1: 10.

In other embodiments, the core (or electrode active material) may be separated from the shell (or encapsulant) by a void space. The compositions and methods according to these embodiments can protect the electrode active material from side reactions with the electrolyte, allow ionic conduction through the encapsulant, and have sufficient void space within the encapsulant and/or encapsulant expansion/contraction properties to accommodate volume changes of the active material during charge and discharge without allowing direct contact between the active material and the electrolyte.

The terms core and electrode active material are used interchangeably herein. Similarly, the terms shell and encapsulant are used interchangeably herein.

In other embodiments, the present disclosure relates to an electrode comprising the core-shell nanoparticles disclosed herein. All aspects and embodiments described in relation to the core-shell nanoparticles and the method of preparing the same are equally applicable to electrodes. In one non-limiting example, the electrode is part of an F-shuttle battery system.

In some embodiments, the present disclosure relates to an electrochemically active structure comprising: a core comprising an active material; and, a fluoride-containing shell at least partially surrounding the active material, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is barium. All aspects described in relation to the preceding embodiments apply to this embodiment with equal force and vice versa.

In some aspects, the active material comprises a metal nanoparticle selected from the group consisting of an iron nanoparticle, a cobalt nanoparticle, a nickel nanoparticle, a copper nanoparticle, a lead nanoparticle, and an alkaline earth metal nanoparticle.

In some aspects, the active material comprises copper nanoparticles.

In some aspects, the fluoride-containing shell is directly attached to the core.

In some aspects, the fluoride-containing shell is spaced apart from the core, thereby defining a void space therebetween.

In some aspects, the second metal is lanthanum.

In some aspects, barium and lanthanum are present in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride-containing shell is 1.

In some aspects, x is from about 0.03 to about 0.15.

In some aspects, x is about 0.03.

In some embodiments, the present disclosure relates to a method of making a coated metal nanoparticle, the method comprising: a) providing a water/metal nanoparticle mixture; b) exposing the water/metal nanoparticle mixture to an inert atmosphere; and c) forming a fluoride-containing shell around the metal nanoparticle core, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is barium. All aspects described in relation to the preceding embodiments apply to this embodiment with equal force and vice versa.

In some aspects, the metal nanoparticles comprise iron nanoparticles, cobalt nanoparticles, nickel nanoparticles, copper nanoparticles, lead nanoparticles, or alkaline earth metal nanoparticles.

In some aspects, the metal nanoparticles comprise copper nanoparticles.

In some aspects, the fluoride-containing shell is directly attached to the core.

In some aspects, the fluoride-containing shell is spaced apart from the core, thereby defining a void space therebetween.

In some aspects, the second metal is lanthanum.

In some aspects, barium and lanthanum are present in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride-containing shell is 1.

In some aspects, x is from about 0.03 to about 0.15.

In some aspects, forming the fluoride-containing shell comprises: adding a first metal salt, a second metal salt, and a fluoride-containing salt to the water/metal nanoparticle mixture to form a fluoride-containing shell around the metal nanoparticle core, wherein the first metal is a barium salt.

In some aspects, the second metal is a lanthanum salt.

In some aspects, the first metal salt is barium nitrate and the second metal salt is lanthanum nitrate.

In some aspects, barium nitrate and lanthanum nitrate are used in a molar ratio of about 1: 10.

In some embodiments, the present disclosure relates to an electrode comprising: a core comprising copper nanoparticles; and, a fluoride-containing shell at least partially surrounding the copper nanoparticles, wherein the fluoride-containing shell comprises barium and lanthanum in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride-containing shell is 1. All aspects described in relation to the preceding embodiments apply to this embodiment with equal force and vice versa.

In some aspects, x is from about 0.03 to about 0.15.

In some aspects, the present disclosure relates to a fluoride ion shuttle battery comprising electrodes and a liquid electrolyte.

In some embodiments, the present disclosure relates to an electrochemically active structure comprising: a core comprising an active material; and a fluoride-containing shell at least partially surrounding the active material, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is a divalent or tetravalent metal cation. All aspects described in relation to the preceding embodiments apply to this embodiment with equal force and vice versa. The fluoride-containing shell may be doped with barium (i.e., to make a barium-doped shell) or with any possible divalent or tetravalent metal cation (i.e., to form a divalent metal cation-doped shell or a tetravalent metal cation-doped shell); in other words, the doping is not limited to doping with barium.

By "inert atmosphere" is meant a gaseous mixture containing little or no oxygen and comprising one or more inert or non-reactive gases having a high threshold before they react. The inert atmosphere may be, but is not limited to, molecular nitrogen or an inert gas such as argon or mixtures thereof.

A "reducing agent" is a substance that causes the reduction of another substance, while itself being oxidized. Reduction refers to the chemical getting one or more electrons, while oxidation refers to the chemical losing one or more electrons.

A "metal salt" is an ionic complex in which the cation is a positively charged metal ion and the anion is a negatively charged ion. "cation" refers to a positively charged ion, and "anion" refers to a negatively charged ion. In the "metal salt" according to the present disclosure, the anion may be any negatively charged chemical species. The metal in the metal salt according to the present disclosure may include, but is not limited to, an alkali metal salt, an alkaline earth metal salt, a transition metal salt, an aluminum salt, or a post-transition metal salt, and hydrates thereof.

An "alkali metal salt" is a metal salt in which the metal ion is an alkali metal ion or a metal in group I of the periodic table, such as lithium, sodium, potassium, rubidium, cesium or francium.

An "alkaline earth metal salt" is a metal salt in which the metal ion is an alkaline earth metal ion or a metal of group II of the periodic Table of the elements, such as beryllium, magnesium, calcium, strontium, barium or radium.

A "transition metal salt" is a metal salt in which the metal ion is a transition metal ion or a metal in the d-block of the periodic Table of elements, including the lanthanides and actinides. Transition metal salts include, but are not limited to, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkolin, californium, fermium, malmium, plutonium, americium, and azulene.

A "late transition metal salt" is a metal salt in which the metal ion is an late transition metal ion such as gallium, indium, tin, thallium, lead, bismuth, or polonium.

A "halide salt" is an ionic complex in which the anion is a halide, including but not limited to fluoride, chloride, bromide, and iodide. A "fluoride salt" is an ionic complex in which the anion is fluoride. According to the present disclosure, the cation of the halide or fluoride salt may be any positively charged chemical species.

"Metal fluorides" are ionic complexes in which the cation is one or more metal ions and the anion is fluoride. According to some aspects of the present disclosure, the one or more metal salts and the fluoride salt react to produce a metal fluoride shell around the metal nanoparticle core. Similarly, a "metal halide" is an ionic complex in which the cation is one or more metal ions and the anion is a halide ion.

A "fluoride-containing" salt is an ionic complex in which the anion contains fluoride but is not limited to only fluoride. In contrast, "fluoride ion-containing" salts include ionic complexes in which the anion contains fluoride ions themselves complexed with other ions or atoms. "fluoride-containing" salts suitable for use in aspects of the present disclosure include those known to those of ordinary skill in the art, including but not limited to fluoride ion salts, non-metallic fluoride-containing anions such as tetrafluoroborates and hexafluorophosphates, and oxyfluoride salts. In some aspects of the present disclosure, fluoride ion-containing salts may include quaternary ammonium fluorides and fluorinated organic compounds. According to some aspects of the present disclosure, the metal salt and the fluoride ion-containing salt react to produce a fluoride-containing shell around the metal nanoparticle core.

The term "electrode" refers to an electrical conductor in which ions and electrons are exchanged with an electrolyte and an external circuit. "positive electrode" and "cathode" are used synonymously in this specification and refer to an electrode that has a higher electrode potential (i.e., is higher than the negative electrode) in an electrochemical cell. "negative electrode" and "anode" are used synonymously in this specification and refer to an electrode having a lower electrode potential (i.e., lower than the positive electrode) in an electrochemical cell. Cathodic reduction refers to the chemical getting one or more electrons, while anodic oxidation refers to the chemical losing one or more electrons. The positive and negative electrodes of the invention can be provided in a range of available configurations and form factors known in the electrochemical and battery science arts, including thin electrode designs, such as thin film electrode configurations. Electrodes are manufactured as known in the art, including, for example, as disclosed in U.S. Pat. No. 4,052,539 and Oxtoby et al, Principles of Modern Chemistry (1999), pp.401-443.

The term "electrochemical cell" refers to a device and/or device component that converts chemical energy into electrical energy or vice versa. Electrochemical cells have two or more electrodes (e.g., a positive electrode and a negative electrode) and an electrolyte, where electrode reactions occurring at the electrode surfaces result in a charge transfer process. Electrochemical cells include, but are not limited to, primary batteries, secondary batteries, and electrolytic systems. General cell and/or battery configurations are known in the art (see, e.g., Oxtoby et al, Principles of Modern Chemistry (1999), pp. 401-443).

"electrolyte" refers to an ionic conductor, which may be in a solid state, a liquid state (most commonly), or less commonly a gas (e.g., plasma).

I. Core-shell nanoparticles comprising a metal core and a metal halide or metal oxyhalide shell in one embodiment, a core-shell nanoparticle is provided comprising a metal core surrounded by a metal halide or metal oxyhalide shell.

In one illustrative example, the core-shell nanoparticles may be included in an electrode of a rechargeable battery, such as an F-shuttle battery. For example, it is difficult to use metal nanoparticles in the electrodes of F-shuttle batteries because the metal will be exposed to conditions that cause undesirable oxidation or dissolution of the metal. Thus, a halide shell is provided that is tailored to protect the metal core nanoparticles from the environment of the electrode while maintaining the desired properties of the metal nanoparticles. In one non-limiting example, the core may comprise copper metal and the shell may comprise LaF₃. In another non-limiting senseIn an illustrative example, the core can comprise copper metal and the core can comprise Ba_xLa_1-xF_3-x。

A method of making core-shell nanoparticles can include providing a first mixture comprising metal nanoparticles and a reducing agent, and mixing the first mixture with a solution comprising one or more metal salts and a halide salt to form a metal halide or oxyhalide shell on the metal nanoparticles. In one non-limiting example, the solution comprises a metal salt and a halide salt. In another non-limiting example, the solution comprises two metal salts and a halide salt. In some such examples, one of the two metal salts is a barium salt. In another such example, the two metal salts comprise a barium salt and a lanthanum salt.

Synthesis and isolation of metal nuclei

Generally, metal nanoparticles used as metal cores can be synthesized by reacting a metal salt solution with a reducing agent in the presence of one or more stabilizing agents. In one illustrative example, the metal salt solution comprises copper (II) nitrate hemipentahydrate (Cu (NO)₃)₂·2.5H₂O) as metal salt. The metal salt is mixed with CTAB and water, and the pH of the mixture can be adjusted to a pH of about 10-11 with, for example, ammonium hydroxide or sodium hydroxide.

The reducing agent may be mixed with one or more stabilizers and water prior to adding the reducing agent to the metal salt solution and for a period of time, such as 20 minutes, prior to combining with the metal salt solution. The reducing agent is selected from the group consisting of hydrazine, sodium borohydride, sodium cyanoborohydride, sodium dithionate, sodium dithionite, iron (II) sulfate, tin (II) chloride, potassium iodide, oxalic acid, formic acid, ascorbic acid, thiosulfate, dithionate, phosphorous acid, phosphite, and hypophosphite. In a preferred embodiment, the reducing agent is hydrazine.

The metal salt solution and the reducing agent are combined to form the metal nanoparticles. The synthesis of the metal nanoparticles is carried out in an oxygen-free atmosphere. Illustrative examples of oxygen-free atmospheres include, but are not limited to, nitrogen, argon, helium, hydrogen, and mixtures thereof. After synthesis, the metal nanoparticles are separated from the synthesis solution. It is to be understood that the method of separating the metal nanoparticles is not limited and may include one or more techniques such as filtration, decantation, and centrifugation. The metal nanoparticles may be washed one or more times with a solvent, such as ethanol, to remove any residual stabilizer or other organic material from their surfaces.

I (b) shell formation

Typically, the isolated metal nanoparticles can be redispersed in an aqueous solution containing additional reducing agent under an oxygen-free atmosphere. The mixture containing the separated metal nanoparticles and the reducing agent is then mixed under an oxygen-free atmosphere with a metal salt solution and a halide salt solution that are used to form a metal halide shell on the metal nanoparticle core. The metal salt solution and the fluoride salt solution for forming the shell may be sequentially added to the nanoparticle mixture, or the metal salt solution and the fluoride salt solution for forming the shell may be simultaneously added to the nanoparticle mixture. In some aspects, the metal salt solution comprises a single metal salt. In other aspects, the metal salt solution comprises two metal salts. In some such aspects, the metal salt solution comprises a barium salt. In some such aspects, the metal salt solution comprises a barium salt and a lanthanum salt. In some such aspects, the metal salt solution comprises barium nitrate and lanthanum nitrate. In some such aspects, the metal salt solution comprises barium nitrate and lanthanum nitrate in a ratio of about 1: 10.

"yolk-shell" nanoparticles

(i) Protective fluoride ion conducting coating

Useful protective encapsulating coatings include fluoride ion conducting phases that are chemically and electrochemically stable in the presence of a liquid FIB electrolyte. These phases allow the exchange of F between the electrolyte and the active material^-. Suitable phases are known in The art and are described, for example, in "The CRC Handbook of Solid State Electrochemistry", Chapter 6(CRC,1997, p.j.gels and h.j.m.bouwmeester, Eds.); sorokin and Sobolev, CrystallographyReports 2007,52,5, 842-; sobolev et al, Crystallography Reports 2005,50,3, 478-; and Trnovcovova et al, Russian Journal of Electrochemistry,2009,45,6, 630-. These bagsIncluding, for example, crystalline phases such as LaF₃、CaF₂、SnF₂、PbF₂、PbSnF₄Similar doping and/or solid solution phases (e.g., La)_0.9Ba_0.1F_2.9、Ca_0.8Y_0.2F_2.2、Ca_0.5Ba_0.5F₂And Pb_0.75Bi_0.25F_2.25) A glass phase of 35InF₃·30SnF₂·35PbF₂And mixed fluoride/other anionic phases such as LaOF. For the purposes of this disclosure, allowing exchange of F between electrolyte and active material^-Higher than 10 at 298K^-10Any material or phase with bulk ionic conductivity of S/cm is within the scope of the invention. These phases are selected by considering the standard redox potentials of the shell constituents and the internal species found in standard cases, so that the constituents are selected to be electrochemically stable at the potentials required for the reaction of the species contained in the cladding. For a more detailed discussion of the selection of coating composition in this regard, see the example of fig. 1G.

Alternative protective coatings include polymers that are conductive to fluoride ions, such as borate functionalized polymers, alkylammonium functionalized polymers, or those having suitable functional groups, such as those described in Gorski et al, anal.

The thickness of the protective coating is selected so that F is between the electrolyte and the active material^-The exchange occurs on a time scale such that charging/discharging of the electrochemical cell can be achieved at a suitable operating rate (e.g., C-rate, corresponding to full charge or discharge of the energy stored in the electrochemical cell within one hour) at about 298K, and will depend on the ionic conductivity of the coating material or phase. For example, LaF₃Or Ba_xLa_1-xF_3-xThe cladding layer(s) of (a) is most useful between 1-200nm thick, for example between about 5nm and about 20nm thick, or any integer or subrange therebetween. More generally, the cladding layer thickness can be from about 1nm to about 1 μm.

The coating may be made by any suitable synthetic methodAnd (4) obtaining. These methods may include solution chemistry techniques such as formation of coatings by precipitation of solids from solutions containing fluorides or their constituent precursors, sol-gel or other soft chemical or "chimie douce" methods, hydrothermal synthesis, vacuum methods such as chemical vapor deposition, physical vapor deposition, sputtering, laser ablation and molecular beam epitaxy, electrochemical deposition, or fluorination of materials after deposition by reaction with a fluorine source. For example, a method for preparing LaF ₃Preferred methods for coating are sol-gel syntheses similar to those described in Ludiger and Kemnitz, Dalton Trans, 2008, 1117-Bu 1127 and Fujihara et al, J.Ceram. Soc. Japan,1998,106, 124-Bu 126, in a suitable solvent (e.g., La (CH) in water₃COO)₃And CF₃COOH) using soluble lanthanum and a fluorine source. The as-prepared clad layer may optionally be subjected to high temperatures in air or an inert gas such as Ar to perform an annealing step, as desired. For example, LaF prepared by a sol-gel process may be used₃The clad layer is heated to 500 ℃ in air to anneal the clad layer and to assist in removing impurities such as solvents. In this manner, the fluoride ion conducting clad phase can be synthesized as desired by adjusting the precursor materials, their stoichiometry, and the annealing step after the initial reaction. The LaF₃The sol-gel synthesis of the coating layer can also be modified by methods known to those of ordinary skill in the art to prepare Ba_xLa_1-xF_3-xThe coating layer of (2).

In another example, La (NO) by suspending nanoparticles of a core material therein₃)₃Slowly adding NH into the aqueous solution₄F, LaF can be obtained by precipitation₃And (4) coating. Due to LaF₃It is very poorly soluble in water, so its crystallization will start on the surface of the suspended nanoparticles. The LaF ₃The precipitation synthesis of the coating may also be modified by methods known to those of ordinary skill in the art to produce Ba_xLa_1-xF_3-xThe coating layer of (2).

Alternatively, La can be prepared using a sol-gel process₂O₃Coating layer, then using F₂Or HF post-fluorinated to convert a substantial portion of the oxideConversion to laOF and/or LaF₃. The sol-gel process can also be used to prepare Ba by methods known to those of ordinary skill in the art_xLa_1-xF_3-xCoating layer of (2)

The fluoride ion-conducting encapsulant and/or the cladding phases and materials can be fabricated on three-dimensional structures (e.g., metal or metal fluoride nanoparticles or aggregates of nanoparticles), two-dimensional structures (e.g., metal or metal fluoride films), or one-dimensional structures (e.g., fibers or tubes of metal or metal fluoride) as desired. Similarly, the fluoride ion conducting phase may be prepared on the outer and/or inner surface of a complex microporous or mesoporous structure such as a zeolite or highly ordered template material. This may include, but is not limited to, mesoporous silicas such as MCM-41 or SBA-15, or metal-organic frameworks or similar coordination polymers.

(ii) Active material encapsulated in a fluoride ion-conducting coating

Useful structures and compositions include those in which the metal or metal fluoride is encapsulated within a fluoride ion conducting cladding (as described in (i) above) such that there is sufficient void space within the encapsulation to accommodate the transition between the metal and metal fluoride phases (or between the lower valence metal fluoride species MFm and the higher valence metal fluoride species MFn, where n is for the same metal M, n is >m) without causing cracking of the cladding phase or material. Such structures and compositions are suitably sized to fit within the fluoride ion-conducting encapsulant, and in some cases, at least sufficient void space is available for up to 100% conversion of the encapsulated metal atoms to the appropriate metal fluoride phase (e.g., as seen in Table 1 for the process Fe → FeF)₃At least 211% void space compared to the starting volume of Fe). In other cases, where there is insufficient void space to achieve 100% conversion, the degree of conversion can be controlled electrochemically (e.g., by controlling voltage limits and/or charge/discharge capacity) such that the encapsulant does not crack during cycling. Additionally, structures and compositions are also contemplated in which the fluoride ion-conducting encapsulant is conformal-having insufficient void space to fully accommodate the conversion of metal to metal fluoride but with adequate void spaceFlexible to stretch or shrink without causing cracking or splitting of the encapsulant. Such compositions may be two-dimensional (e.g., membrane-void-coating) or three-dimensional (e.g., nanoparticle-void-coating, or more complex arrangements such as metal impregnated zeolite-void-coating), as desired.

In other embodiments, a plurality of concentrically arranged encapsulants are contemplated. Each concentrically arranged encapsulant may be separated by a void and may be constructed of the same or different materials. In other embodiments of concentrically arranged encapsulants, the active material and the outermost encapsulant (the encapsulant contacting the electrolyte) can be separated by a polymer or other flexible material capable of allowing passage of fluoride ions and sized to accommodate volume changes upon cycling to rupture the outermost encapsulant.

It is to be understood that structures in which the active material is completely surrounded and located within the encapsulant, but which have at least some residual void space and/or compressible inactive material (e.g., polymer) may be referred to as "egg yolk-shell" nanocomposite structures. Such a fully encapsulated structure may be based on various compositional arrangements of the active material and the fluoride ion-conducting encapsulant. However, other arrangements are also contemplated in which the active material is contained only partially surrounded by a fluorine ion conducting protective cladding. Such structures may include two-dimensional or three-dimensional non-fluorine ion-conducting support structures (e.g., membranes, open-ended channels, tubes, etc.) containing an active material having one or more sides coated with a fluorine ion-conducting material to allow ion transport. Such support structures may comprise a polymer or other material that is void space or dimensionally flexible to accommodate volume changes upon cycling without causing rupture of the support structure or encapsulant.

A general preparation strategy for "yolk-shell" nanocomposite structures is described in Lou et al, adv. The metal "yolk" material in question is typically Au, which is not considered a useful active material for FIB electrochemical cells. Also, the "shell" material described is typically SiO₂It is not considered a useful fluoride ion conducting material. Thus, the following outlines the applications that may be used for FIB electrochemicalSuitable preparation strategies for "yolk-shell" nanocomposites in chemical cells. These strategies are intended to be illustrative and not limiting of the invention. In certain examples, Cu metal or CuF₂Will be used as an example of an active material "egg yolk", and LaF₃Examples of materials that will be used as an encapsulant or "shell"; as previously mentioned, these examples do not limit the invention, since any material capable of containing or releasing fluoride ions at the time of electrochemical reaction can be envisaged to constitute the "egg yolk" and it is envisaged to allow the exchange of F between the electrolyte and the active material^-Any phase or material of (a) to form an encapsulant or shell. In certain embodiments, the active material is less than 1 micron in diameter, most usefully, the active material "egg yolk" is between 1 to 500nm in diameter, and the encapsulant has a thickness of 2 to 100 nm.

FIG. 1B outlines the use of sacrificial inorganic "intermediate" layers such as SiO₂General route (c). For example, Cu can be reduced by using hydrazine or similar reducing agents in the presence of stabilizing and/or coordinating species such as sodium citrate and/or surfactants (e.g., cetyltrimethylammonium bromide)²⁺Ionic solution to prepare Cu nanoparticles. The Cu nanoparticles are exposed to a surface modifying ligand such as aminopropyltrimethoxysilane APTS (or other suitable bifunctional species such that one part of the molecule coordinates with the Cu surface while another part provides a reactive silicon moiety to the external environment), and then under suitable conditions (e.g.,

synthesis or sol-gel reaction), a hydrolyzable silica source such as tetraethyl orthosilicate (TEOS) or sodium silicate solution (water glass) is added to coat the Cu nanoparticles with SiO₂And (4) coating in a conformal way. SiO 2₂The thickness of the layer (and hence the void space) can be varied by varying the SiO used₂The amount of precursors and the reaction conditions. Followed by coating with SiO by a sol-gel reaction, optionally in the presence of a surfactant such as Lutensol AO₂Coated with LaF₃In which the LaF used can be passed₃The amount of the precursor and the reaction conditions are used to change the thickness of the coating layer And (4) degree. This step can be used to isolate and/or purify the intermediate Cu @ SiO₂The material is followed or may be formed after forming SiO₂The layers are then carried out in the same reaction mixture. Resulting Cu @ SiO₂@LaF₃The composite may optionally be subjected to an annealing step, and/or may then be subjected to a thermal annealing step by exposing the composite to SiO under suitable conditions₂Etchant materials such as NaOH or HF to remove SiO₂Layer to provide Cu @ LaF₃An egg yolk-shell composition. The material may then be subjected to a final annealing step, optionally in the presence of a reducing agent such as H₂To purify the Cu surface.

Figure 1C depicts a similar route using a sacrificial polymer "middle" layer. For example, Cu nanoparticles are coordinated from the polymer shell by forming Cu nanoparticles in the presence of polymers or copolymers with amino-, hydroxyl-, carboxylate, or other ionizable functional groups, such as poly (acrylic acid), poly (ethyleneimine), poly (vinyl alcohol), poly (styrene sulfonate), proteins, polysaccharides, or gelatin, or by growing polymers from the surface of suitably modified Cu nanoparticles (e.g., growing poly (styrene sulfonate) from 11-aminoundecyl 2-bromoisobutyrate functionalized surfaces by atom transfer radical polymerization). The thickness of the polymer layer (and hence the void space created) can be controlled by the polymer concentration and/or molecular weight. LaF growth around the outside of the Cu @ polymer nanocomposite by sol-gel reaction ₃To provide a Cu @ polymer @ LaF₃A nanocomposite. The polymer layer is then removed by decomposition at elevated temperature (in air or under an inert gas such as Ar), or dissolution in a suitable solvent (e.g., toluene, dichloromethane, or acetone) to give the desired Cu @ LaF₃An egg yolk-shell composition. The material may then be subjected to a final annealing step, optionally in the presence of a reducing agent such as H₂To purify the Cu surface. Alternatively, a polymeric core-shell structure such as the hollow latex-type particles described in McDonald and Devon, adv.colloid.Interf.Sci.,2002,99,181-213 may be used as a template in which Cu nanoparticles are trapped (either by exposing the Cu nanoparticles to preformed hollow latex particles, or by combining Cu ions in solution with electrically chargeable hollow latex particlesCoordination of the isolated prepolymer or copolymer, then reduction of the Cu ions to give Cu nanoparticles and then generation of hollow structures by, for example, removal of the solvent), followed by growth of LaF as desired₃Shell, polymer removal and annealing to form Cu @ LaF₃An egg yolk-shell composition.

FIG. 1D depicts an alternative route without sacrificing the "middle" layer. For example, in growing LaF by sol-gel reaction ₃Before the outer layer(s), the Cu nanoparticles are treated with a suitable surface modifying ligand (e.g., 11-aminoundecanoic acid, AUDA) to give Cu @ LaF₃A "core-shell" complex, which may then optionally be subsequently subjected to an annealing step. Using a suitable etchant (e.g., KCN, HCl/H)₂O₂Or FeCl₃(ii) a Suitable Etchants for a wide range of metals and compounds are given in "The crcheandbook of Metal etchings" (CRC,1990, p.walker and w.h.tarn eds.), and may be selected so as not to affect The "shell" material) to partially etch The Cu "core" and will be able to etch at Cu @ LaF by controlling The reaction conditions (e.g., etchant concentration, temperature, reaction time)₃Void spaces are created in the particles to provide a "yolk-shell" Cu @ LaF₃A composition is provided. The material may then be subjected to a final annealing step, optionally in the presence of a reducing agent such as H₂To purify the Cu surface.

FIG. 1E depicts a variation of the above-described "sacrificial" synthesis, in which nanoparticles of an active material are grown on the surface of a "sacrificial" material (here, it is the innermost material that is removed). For example, in amino-functional poly (styrene) s or SiO₂One or more Cu nanoparticles are grown on the surface of the particles. Treating the resulting composite with a suitable Cu surface-modifying ligand (e.g., AUDA), followed by growth of LaF by sol-gel reaction ₃An outer layer of (a). Removing the innermost material by thermal decomposition, etching or dissolution to produce a "yolk-shell" Cu @ LaF with one or more Cu nanoparticles₃A composition is provided. The material may then be subjected to a final annealing step, optionally in the presence of a reducing agent such as H₂To purify the Cu surface and optionally to agglomerate the Cu nanoparticles.

Fig. 1F outlines an alternative strategy in which the active material is grown in the internal structure or pores of a pre-formed "sacrificial" material. For example, the Cu nanoparticles may be in hollow SiO₂Nanosphere in-growth (see, e.g., Hah et al, chem. Commun.,2004, 1012-. These Cu @ SiO are then reacted by a sol-gel reaction, optionally in the presence of a surfactant such as Lutensol AO₂Core-shell nanocomposites coated with LaF₃In which the LaF used can be passed₃The amount of precursor and the reaction conditions vary the thickness of the coating. Resulting Cu @ SiO₂@LaF₃The composite may optionally be subjected to an annealing step, and/or may then be subjected to a thermal annealing step by exposing the composite to SiO under suitable conditions₂Etchant materials such as NaOH or HF to remove SiO₂Layer to provide Cu @ LaF₃An egg yolk-shell composition. The material may then be subjected to a final annealing step, optionally in the presence of a reducing agent such as H ₂To purify the Cu surface. In a related synthesis, a microporous or mesoporous material such as zeolite can be used as a "template" for the formation of Cu nanoparticles, followed by the subsequent generation of Cu @ LaF in a similar manner₃"yolk-shell".

FIG. 1G also depicts a similar alternative strategy in which a highly electropositive metal or metal fluoride thereof, such as CaF, is grown in a suitable solvent within the interior space of a hollow material, such as a poly (styrene) -poly (acrylic acid) latex copolymer₂. These polymer encapsulated cafs are then coated with an outer layer of fluoride ion conducting material of suitable electrochemical stability₂Nanocrystals of the so as to be in CaF₂Conversion potential to Ca (vs. Li)⁺Li, 0.2V) does not reduce by itself. Examples of suitable protective materials include solid solutions such as Ca_xBa_yF₂(x + y ═ 1), where Ca in the protective shell²⁺And Ba²⁺CaF ion in shell₂The particles are not greatly reduced in the conversion reaction process; in contrast, a shell having a lower electropositive metal element (e.g., LaF)₃) Will itself take precedence over internal CaF₂The particles are reduced. The CaF thus obtained₂@ Polymer @ Ca_xBa_yF₂The composite may optionally undergo an annealing step, and/or the polymer layer may then be removed by exposing the composite to an elevated temperature or a suitable solvent etchant material that removes the polymer to yield CaF ₂@Ca_xBa_yF₂An egg yolk-shell composition.

The encapsulated active material and/or yolk-shell nanocomposite electrode can be used in conjunction with electrolytes, binders, additives, separators, battery casings or packages, current collectors, electrical contacts, electronic charge and discharge controllers, and other battery construction elements known to those skilled in the art to produce useful lithium-free electrochemical cells operable at temperatures ranging from-40 ℃ to 200 ℃. Such electrochemical cells may have substantially irreversible electrochemical reactions during discharge, making them suitable for forming primary cells or primary cells. Alternatively, certain structures and compositions having electrochemical reactions can be at least partially reversible by the application of a charge, and can form secondary (rechargeable) batteries.

In certain embodiments, an electrolyte suitable for a FIB battery system can include a fluoride ion salt and a solvent, where the fluoride ion salt is at least partially present in solution. The fluoride ion salt may be a metal fluoride or a non-metal fluoride. The solvent may be an organic liquid or an ionic liquid, or a mixture of both. In other embodiments, electrolytes suitable for FIB cell systems can include composite electrolytes containing fluoride salts, polymers, and optionally organic liquids, ionic liquids, or mixtures of both. The electrolyte may include, but is not limited to, a combination of Fluoride Ion salts and solvents disclosed in U.S. patent 9,166,249 entitled "Fluoride Ion Battery Compositions," the disclosure of which is incorporated herein by reference.

For example, a liquid electrolyte salt suitable for FIB systems may contain a complex cation in combination with a fluoride anion. The cation may be characterized as an organic group, such as an alkylammonium, alkylphosphonium, or alkylsulfonium species, or may be composed of a metal-organic or metal-coordination complex, such as a metallocene species. Useful solvents for such liquid electrolyte salts may include non-aqueous solvents (herein "organic") capable of dissolving the above-described fluoride salts to molar concentrations of 0.01M and higher, preferably to concentrations between 0.1 and 3M. Examples of such solvents include acetone, acetonitrile, benzonitrile, 4-fluorobenzonitrile, pentafluorobenzonitrile, Triethylamine (TEA), diisopropylethylamine, 1, 2-dimethoxyethane, ethylene carbonate, Propylene Carbonate (PC), γ -butyrolactone, dimethyl carbonate, diethyl carbonate (DEC), methylethyl carbonate, methylpropyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, nitromethane, benzene, toluene, chloroform, dichloromethane, 1, 2-dichloroethane, dimethyl sulfoxide, sulfolane, N-Dimethylformamide (DMF), N-Dimethylacetamide (DMA), carbon disulfide, ethyl acetate, methyl butyrate, N-propyl acetate, methyl propionate, methyl formate, 4-methyl-1, 3-dioxolane, pyridine, methyl isobutyl ketone, methyl ethyl ketone, ethyl methyl ether, Hexamethylphosphoramide, hexamethylphosphoric triamide, 1-methyl-2-pyrrolidone, 2-methoxyethyl acetate, trimethyl borate, triethyl borate and substituted derivatives thereof, and sulfones such as ethylmethyl sulfone, trimethylene sulfone, 1-methyltrimethylene sulfone, ethyl sec-butyl sulfone, ethyl isopropyl sulfone (EIPS), 3,3, 3-trifluoropropyl methyl sulfone, 2,2, 2-trifluoroethyl sulfone, bis (2,2, 2-trifluoroethyl) ether (BTFE), ethylene glycol dimethyl ethers (e.g., diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether), 1, 2-Dimethoxyethane (DME), and mixtures thereof. In certain embodiments, room temperature Ionic liquid materials or Ionic Liquids that remain liquid at temperatures below 200 degrees Celsius (such as those described in "Electrochemical assays of Ionic Liquids", E.Ohno et al, Wiley Interscience, New York, 2005) are preferred. These may include ionic liquids that remain liquid at temperatures below 100 degrees celsius, such as 1-methyl 1-propylpiperidinium bis (trifluoromethanesulfonyl) imide (MPPTFSI), butyltrimethylammonium bis (trifluoromethanesulfonyl) imide (BTMATFSI), and 1-butyl 1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (BMPTFSI) and their Fluoroalkylphosphate (FAP) anion derivatives (e.g., mpp), where FAP is a hydrophobic anion such as tris (pentafluoroethyl) trifluorophosphate, all alone or in combination, are useful solvents.

In certain other embodiments, electrolytes suitable for FIB cell systems can include the compositions disclosed above, wherein a fluoride ion complexing species such as an anion receptor, a cation complexing species such as a crown ether, or a combination of both are added. Suitable anion acceptors include species capable of binding fluoride anions such as boron, aluminum, ammonium, H-bond donors or similar groups, including aza ether and alkyl and aryl boron and borate complexes such as those described in McBreen et al, j.power Sources,2000,89,163 and West et al, j.electrochem. soc.,154, a929(2007), and boroxine species such as those described in Nair et al, j.phys. chem.a,113,5918(2009), all of which are incorporated herein by reference. In particular, tris (hexafluoroisopropyl) borate, tris (pentafluorophenyl) borane, and all possible positional isomers of Difluoroboroxine (DFB), trifluorophenylboroxine, bis (trifluoromethyl) phenylboroxine, and fluoro (trifluoromethyl) phenylboroxine may be used.

It is understood that fluoride ion batteries are suitable for a wide range of primary or rechargeable applications, including but not limited to vehicle traction batteries (electric vehicles (EV), Hybrid Electric Vehicles (HEV), and plug-in hybrid electric vehicles (PHEV)) or vehicle starters or ignition batteries. FIB systems may be useful stationary batteries for emergency power, local energy storage, starter or ignition, remote relay stations, communication base stations, Uninterruptible Power Supplies (UPS), spinning reserve, peak shaving or load balancing, or other grid storage or optimization applications. And may be used in miniature or miniature appliances, including watch batteries, implantable medical device batteries, or sensing and monitoring system batteries (including gas or electronic metering), as well as other portable applications such as flashlights, toys, power tools, portable radios and televisions, cellular telephones, camcorders, laptops, tablets or handheld computers, portable instruments, cordless devices, wireless peripherals, or emergency beacons. Military or extreme environmental applications, including use in satellites, munitions, robots, unmanned flying vehicles, or for military emergency power or communications are also possible.

III (c): comparative example 1 and Experimental example 1

In comparative example 1In (1), copper nanoparticles without shell were prepared and analyzed. First, 2mmol of Cu (NO) was added at room temperature₃)₂·2.5H₂O and 1.87mmol CTAB were dissolved in 75ml of water, and 0.5ml of NH was added₄OH (28-30% by weight NH)₃Water, 14.8M) to adjust the pH to about 10-11. A solution of hydrazine (3ml of 50-60% reagent grade), CTAB (1.87mmol) and citric acid (0.38mmol) in water (75ml) was prepared under argon and mixed for about 20 minutes before copper nitrate solution was added. The reaction mixture was stirred for 1.5 hours to maximize the growth of copper nanoparticles. The resulting copper nanoparticles (. about.50 nm) were isolated and washed. Specifically, the reaction synthesis mixture was centrifuged, decanted, mixed with ethanol and sonicated. Fig. 3 shows an X-ray diffraction (XRD) spectrum of the as-prepared copper nanoparticles. Three peaks are visible, each corresponding to Cu (° 2 θ): 43.0, 50.5 and 74.0. However, upon exposure to air, Cu is oxidized to Cu₂O, which starts to form at least as early as 4 days and is the main product after 9 days. This is illustrated in fig. 4, which shows the appearance of new peaks at 29.5, 42.3, 61.3 and 73.5 ° 2 θ, corresponding to Cu₂O。

In experimental example 1, core-shell nanoparticles, comprising a core including copper nanoparticles, comprising lanthanum fluoride (Cu/LaF), were prepared according to the present disclosure ₃) Is coated by the shell. Copper nanoparticles of 50nm were prepared using the same method as comparative example 1, but re-dispersed in water with 3ml of hydrazine (3ml of 50-60% reagent grade) under argon atmosphere after separating and washing the copper nanoparticles. Adding La (NO) to a mixture of water, copper nanoparticles and hydrazine₃)₃·6H₂O (1mmol in 15ml H₂In O) and NaF (1mmol in 15ml H)₂O) in solution. The reaction mixture was stirred for 10 minutes and then centrifuged.

The precipitate was separated by centrifugation and analyzed by XRD. The XRD pattern of the as-synthesized core-shell nanoparticles is shown in fig. 5. The XRD pattern showed 5 peaks (° 2 θ): 25.0 (LaF)₃)、28.0(LaF₃) 43.5(Cu), 50.4(Cu), 74.0 (Cu). Figure 6 shows stacked XRD patterns of the core-shell nanoparticles after exposure to air for 9 days, 16 days, and 23 days. In comparison with the comparative example 1, the present inventors have conducted a study,no spectral change was observed. Fig. 7A and 7B show TEM images of as-synthesized core-shell nanoparticles. As shown, the copper nanoparticle core is LaF₃The shell is covered. The thickness of the shell is about 0.30 nanometers. Figures 8A-8C show high resolution TEM images of core-shell nanoparticles in the as-synthesized state. The central black region corresponds to the copper core, and the peripheral black and white regions correspond to the LaF ₃And (4) a shell. These figures show direct coating with LaF₃Uniform coverage of the copper core of the shell.

Thus, the core-shell nanoparticles synthesized in experimental example 1 provide a shell capable of protecting the underlying metal core. Such core-shell nanoparticles may be useful in applications where operating conditions may dissolve, oxidize, or otherwise contaminate the metal core. Illustrative examples include the use of the core-shell nanoparticles as battery electrode materials.

In a non-limiting example as shown in fig. 9, the core-shell nanoparticles of experimental example 1 may be included as an active material in the negative electrode (anode) of the F-shuttle cell. LaF₃The shell protects the copper core, allowing it to operate as an active material without being dissolved. As shown in fig. 10A and 10B, the core-shell nanoparticles of experimental example 1 were tested as an active material in an anode. The anode comprises core-shell nanoparticles, a conductive agent (Super P carbon black) and a PVdF binder in a ratio of 8:1: 1.

Comparative example 2

Attempts were made to prepare core-shell nanoparticles comprising a core comprising copper nanoparticles, and comprising lanthanum fluoride (Cu/LaF)₃) The shell of (a) is directly coated. Comparative example 2 was carried out in the same manner as in Experimental example 1, except that 1mmol of LaCl was used₃·7H₂O instead of La (NO) ₃)₃·6H₂O。

The XRD pattern of the as-synthesized nanoparticles in comparative example 2 is shown in fig. 11. The XRD pattern showed 5 peaks (° 2 θ): 24.5 (LaF)₃)、27.6(LaF₃) 43.6(Cu), 50.5(Cu), 74.1 (Cu). Thus, Cu in LaCl₃And remains during the reaction with NaF.

However, oxidation of Cu after core-shell nanoparticle exposure of comparative example 2 indicates that the shell is not adequateIs formed. Fig. 12 shows stacked XRD patterns of the nanoparticles synthesized in comparative example 2 after exposure to air for 8 days, 15 days, and 22 days. Additional peaks (° 2 θ) were observed from day 8 onward: 35.4, 36.4, 38.8, 42.5, 44.8, 48.7, 52.3, 61.5, 73.5. Peaks at least at 36.4, 42.5, 61.5 and 73.5 DEG 2 theta with Cu₂The formation of O is consistent. The peaks at 43.6, 50.5 and 74.1 ° 2 θ, which are consistent with Cu, are also reduced in intensity. As shown in FIG. 13, TEM image showed that Cu nanoparticles are LaF₃And LaF unassociated with Cu nanoparticles₃Is not uniformly partially covered. Thus, with LaCl₃·7H₂The shell made of O does not produce the desired core-shell composition because it exposes the Cu core to the electrochemical cell environment where the Cu core may dissolve. In addition, LaF not associated with Cu nanoparticles₃The overall efficiency of any system incorporating the mixture is reduced.

Study of layered thin film electrode

Core and shell materials can also be studied in thin film electrode configurations. Briefly, copper was sputtered onto a 1mm thick glassy carbon substrate to a thickness of about 80 nm. After forming the Cu film, LaF is sputtered onto the Cu layer₃To a thickness of less than 5nm to form a double-layered thin film; for comparison purposes, no LaF was also prepared₃A single layer Cu film of a clad layer. The films were studied in a three-electrode cell configuration with Ag-wire as reference electrode, Pt-wire as counter electrode, soaked in 1-methyl-1-propylpyrrolidinium bis (trifluoromethylsulfonyl) imide (MPPyTFSI) and 0.01MAgOTf, and 0.1M tetramethylammonium fluoride (TMAF) as electrolyte in MPPyTFSI. In contrast to Ag/Ag⁺The cyclic voltammogram was measured in the range of-2.4V to-0.7V. The evaluation was carried out in a glove box containing no moisture and oxygen.

The resulting cyclic voltammogram is shown in FIG. 14. For the bilayer film, the anodic peak was measured to be symmetrical to the cathodic peak, and no copper ions were detected in the electrolyte by ICP-MS. These results indicate that fluoride ions were later formed from LaF₃Reversible transport of the layer into Cu. In contrast, the cyclic voltammogram obtained for a single layer Cu film is asymmetric. The anodic current exceeds the cathodic current, indicating that Cu has reacted at the anode Dissolving in the process. The ICP-MS data confirmed this, showing 5ppm Cu in the electrolyte.

Cu-LaF was also studied by XPS initially and after fluorination at the voltages shown in FIG. 15A₃A double-layer thin film electrode. The study at the initial time point (1 in fig. 15A) corresponds to the deposition state. The potential was then driven from OCV (vs. Ag/Ag)⁺about-1.5V) was scanned to-0.8V and held for 1 hour. After the fluorination reaction, a sample of the electrode was taken for XPS depth profiling analysis.

In the initial XPS spectrum (fig. 15B), the surface contained more La and F than Cu. After fluorination, higher levels of fluoride ions can be detected at deeper depths than the initial XPS spectra; in the initial spectrum, the fluoride level dropped more sharply with increasing depth. In general, XPS data indicates that fluoride ions can penetrate into the copper layer. Therefore, fluorine ions may diffuse into the Cu nuclei after reduction.

Example 3

Having the formula Cu @ Ba_xLa_1-xF_3-xThe core-shell nanoparticles of the shell of (a) are schematically shown in fig. 16; comprises Cu @ LaF₃For comparison. Initially, the copper nanoparticle core may be up to about 50nm in diameter, and the LaF₃Or Ba_xLa_1-xF_3-xThe cladding layer may be about 5nm thick. CuF forming Cu nuclei during battery charging₂The layer can be in Cu @ LaF ₃The nanoparticles were grown to a thickness of about 3 nm. However, by applying in LaF₃Doping the shell with CuF₂The layer may be grown to a greater thickness.

LaF₃The ionic conductivity of (a) is rather low, especially at room temperature. It is only about 10^-8.5S/Cm, limiting F anion transport. However, in LaF₃The shell includes a Ba dopant (i.e., preparation of Cu @ Ba)_xLa_1-xF_3-x) Increasing the conductivity of the shell. LaF has been reported₃The conductivity of (b) is increased by 100 times when doping Ba; see m.anji Reddy and m.fichtner, Batteriesbased on fluoride shunt, j.mater.chem.2011,21,17059-17062, which are incorporated herein by reference in their entirety. High ionic conductivity for CuF during charging₂Is generated byAdvantageously, resulting in increased capacity.

Exemplary Cu @ Ba_xLa_1-xF_3-xSEM, TEM, and EDX images of the nanoparticles are included in FIGS. 17A-H. XPS can be used to determine the composition of each element. FIGS. 18A-D show representative XPS spectra data for core @ shell nanoparticles containing Cu (64.83%), La (14.68%), Ba (0.28%), and F (20.21%), where the shell itself contains La (41.75%), Ba (0.79%), and F (57.46%), confirming that the nanoparticles are Cu @ La_0.97Ba_0.03F_2.97。Cu@LaF₃And Cu @ La_0.97Ba_0.03F_2.97The XRD pattern of (A) is shown in FIG. 19.

Fig. 20A-20B illustrate the capacity improvement achieved upon Ba doping according to some aspects of the present disclosure. FIG. 20A shows Cu @ LaF ₃Electrodes or Cu @ Ba_xLa_1-xF_3-xVoltage curve of first charge-discharge cycle of electrode, which is compared with Ag/Ag⁺Reference electrode comparison. The capacity delivery of the Ba-doped electrode reaches 95.2mAh/g and Cu @ LaF₃Compared to only 50.2mAh/g (FIG. 20B). Thus LaF₃The Ba doping of the shell almost doubles the capacity. By doping with Ba, LaF₃The ionic conductivity of the shell is improved by about 100 times; see, e.g., m.anji Reddy and m.fichtner, Batteries based on fluoride shunt, j.mater.chem.2011,21,17059-17062, which are incorporated herein by reference in their entirety. The fluoride ions can readily migrate across the shell to react with Cu to form CuF₂And CuF₂The amount of formation directly determines the capacity of the battery. Formed CuF₂The more, the higher the capacity of the battery. Therefore, the utilization rate of Cu can pass through LaF₃The shell is doped Ba to approximate multiplication.

Further, fig. 20C and 20D show Cu @ La, respectively_0.97Ba_0.03F_2.97And Cu @ LaF₃As well as XRD patterns after the first charge and the subsequent first discharge. CuF₂May be formed after a first charge and then reduced to Cu after a first discharge. Fig. 20C and 20D show that Cu can circulate in the liquid electrolyte with both types of shells.

Cu is a good cathode material for fluoride ion shuttle cells because it is inexpensive, is a light metal, and has a high capacity (theoretical capacity of 843.5 mAh/g). However, a major challenge for its use is that Cu cannot be charged in the liquid electrolyte/cell to form CuF due to its dissolution₂. For Cu @ LaF₃，LaF₃The shell effectively avoids the dissolution of Cu during the charge/discharge process. As a result, Cu can be charged to CuF during charging₂And CuF₂Can be reduced to Cu during discharge. But its capacity is due to LaF₃Low ion conductivity. Shell doped by Ba (e.g. La)_0.97Ba_0.03F_2.97) The ionic conductivity of the shell can be increased by a factor of 100, i.e. the shell has a low electrical resistance. The F ions pass through the shell more easily so that more Cu can be fluorinated to CuF during charging₂. With undoped LaF₃Shell-by-shell, the capacity is multiplied. By Ba-doped shells, CuF₂Can be detected after charging. CuF₂And is reduced to Cu after discharge. It was confirmed that Cu was rechargeable in the liquid cell and Cu utilization was improved by the Ba doped shell.

While the aspects described herein have been described in conjunction with the example aspects outlined above, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that may be presently unforeseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the example aspects set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the disclosure. Accordingly, the present disclosure is intended to embrace all known or later-developed alternatives, modifications, variations, improvements, and/or substantial equivalents.

Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. Claim elements should not be construed as means-plus-function unless the element is explicitly recited using the expression "means for … …".

Moreover, the term "example" is used herein to mean "serving as an example, instance, or illustration. Any aspect described herein as "an example" is not necessarily to be construed as preferred or advantageous over other aspects. The term "some" means one or more unless specifically stated otherwise. Combinations such as "A, B or at least one of C", "at least one of A, B and C", and "A, B, C or any combination thereof" include any combination of A, B and/or C, and may include multiples of a, multiples of B, or multiples of C. Specifically, combinations such as "at least one of A, B or C", "at least one of A, B and C", and "A, B, C or any combination thereof" may be a only, B only, C, A and B, A and C, B and C, or a and B and C, wherein any such combination may contain one or more members of A, B or C. Nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

These examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, dimensions, etc.) but some experimental error and deviation should be accounted for.

Moreover, all references, e.g., patent documents, including issued or granted patents or equivalents, patent application publications, non-patent documents, or other source materials, are herein incorporated by reference in their entirety as if each were individually incorporated by reference.

Claims (25)

1. An electrochemically active structure comprising:

a core comprising an active material; and

a fluoride-containing shell at least partially surrounding the active material;

wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is barium.

2. The electrochemically active structure of claim 1, wherein the active material comprises metal nanoparticles selected from the group consisting of iron nanoparticles, cobalt nanoparticles, nickel nanoparticles, copper nanoparticles, lead nanoparticles, and alkaline earth metal nanoparticles.

3. The electrochemically active structure of claim 1, wherein the active material comprises copper nanoparticles.

4. The electrochemically active structure of claim 1, wherein the fluoride-containing shell is directly attached to the core.

5. The electrochemically active structure of claim 1, wherein the fluoride-containing shell is spaced from the core to define a void space therebetween.

6. The electrochemically active structure of claim 1, wherein the second metal is lanthanum.

7. The electrochemically active structure of claim 6, wherein barium and lanthanum are present in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride-containing shell is 1.

8. The electrochemically active structure of claim 7, wherein x is from about 0.03 to about 0.15.

9. The electrochemically active structure of claim 8, wherein x is about 0.03.

10. A method of making a coated metal nanoparticle, the method comprising:

a) providing a water/metal nanoparticle mixture;

b) exposing the water/metal nanoparticle mixture to an inert atmosphere; and

c) forming a fluoride-containing shell around the metal nanoparticle core, wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is barium.

11. The method of claim 10, wherein the metal nanoparticles comprise iron nanoparticles, cobalt nanoparticles, nickel nanoparticles, copper nanoparticles, lead nanoparticles, or alkaline earth metal nanoparticles.

12. The method of claim 10, wherein the metal nanoparticles comprise copper nanoparticles.

13. The method of claim 10, wherein the fluoride-containing shell is directly attached to the core.

14. The method of claim 10, wherein the fluoride-containing shell is spaced apart from the core to define a void space therebetween.

15. The method of claim 10, wherein the second metal is lanthanum.

16. The method of claim 15, wherein barium and lanthanum are present in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride-containing shell is 1.

17. The method of claim 16, wherein x is from about 0.03 to about 0.15.

18. The method of claim 10, wherein said forming said fluoride-containing shell comprises: adding a first metal salt, a second metal salt, and a fluoride-containing salt to the water/metal nanoparticle mixture to form a fluoride-containing shell around a metal nanoparticle core, wherein the first metal is a barium salt.

19. The method of claim 18, wherein the second metal salt is a lanthanum salt.

20. The method of claim 19, wherein the first metal salt is barium nitrate and the second metal salt is lanthanum nitrate.

21. The method of claim 20, wherein barium nitrate and lanthanum nitrate are used in a molar ratio of about 1: 10.

22. An electrode, comprising:

a core comprising copper nanoparticles; and

a fluoride-containing shell at least partially surrounding the copper nanoparticles,

wherein the fluoride containing shell comprises barium and lanthanum in a ratio of x to 1-x such that the sum of the moles of barium and the moles of lanthanum in the empirical formula for the fluoride containing shell is 1.

23. The electrode of claim 22, wherein x is from about 0.03 to about 0.15.

24. A fluoride ion shuttle battery comprising the electrode of claim 22 and a liquid electrolyte.

25. An electrochemically active structure comprising:

a core comprising an active material; and

a fluoride-containing shell at least partially surrounding the active material,

wherein the fluoride-containing shell comprises a first metal and a second metal, and the first metal is a divalent or tetravalent metal cation.

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