Functionalized boron nitride materials as electroactive species in electrochemical energy storage devices

Abstract

There is provided an improved electrochemical energy storage device. The storage device includes using functionalized boron nitride nanoparticles as electroactive materials in the electrodes.

Claims

1. An electrochemical energy storage device comprising: a positive electrode including a first electrode potential, the positive electrode comprising a positive electrode current collector, a porous, electrically and ionically conducting matrix in contact with the positive electrode current collector, and aprotic covalently functionalized boron nitride nanoparticles embedded in the porous, electrically and ionically conducting matrix, both electrons and ions are conducted to the functionalized boron nitride nanoparticles; an aprotic negative electrode consisting of at least one material selected from the group consisting of Li, Na, K, Be, Mg, Ca and Al, the aprotic negative electrode including a second electrode potential that is more negative than the first electrode potential of the positive electrode; at least one conductor ionically connecting the positive electrode to the aprotic negative electrode, the conductor transporting positive ions released by the aprotic negative electrode during a discharge cycle of the electrochemical energy storage device and absorbed by the aprotic negative electrode during a charge cycle; discharging of the electrochemical energy storage device producing a reduced form of the functionalized boron nitride nanoparticles, and charging of the electrochemical energy storage device produces an oxidized form of the corresponding functionalized boron nitride nanoparticles; electrons and ions are simultaneously absorbed by and stored in the functionalized boron nitride nanoparticles during the discharge cycle, and released during the charge cycle; the charge storage capacity of the positive electrode originating from functionalized boron nitride nanoparticles in a body of the porous, electrically and ionically conducting matrix.

2. The electrochemical energy storage device of claim 1, wherein the covalently functionalized boron nitride nanoparticles include covalently functionalized forms of at least one of hexagonal boron nitride, boron nitride nanotubes, cubic boron nitride, and amorphous boron nitride.

3. The electrochemical energy storage device of claim 1, wherein the covalently functionalized boron nitride nanoparticles comprise a surface including a carbon coating, a polymer coating, or a coating comprising porous hard materials including Si.sub.3N.sub.3 and SiS.sub.2.

4. The electrochemical energy storage device of claim 1, wherein the covalently functionalized boron nitride nanoparticles comprise being functionalized with at least one of: alkyl groups selected from the group consisting of methyl (—CH.sub.3), ethyl (—CH.sub.2—CH.sub.3), propyl (—(CH.sub.2).sub.2—CH.sub.3), butyl (—(CH.sub.2).sub.3—CH.sub.3), isopropyl (CH(CH.sub.3).sub.2), isobutyl (—CH.sub.2—CH(CH.sub.3).sub.2), and tertiary butyl (—C(CH.sub.3).sub.3), at least one of phenyl (—C.sub.6H.sub.5) and substituted phenyl, alkoxy groups selected from the group consisting of methoxy (—O—CH.sub.3), ethoxy (—O—CH.sub.2—CH.sub.3), propoxy (—O—(CH.sub.2).sub.2—CH.sub.3), and butoxy (—O—(CH.sub.2).sub.3—CH.sub.3), oxo (—O—), peroxo (—O═O—), sulfo (—S—), disulfo (—S—S—), nitrozo (—N═O), carbonyl (—C≡O), cyano (—C≡N), isocyano (—N≡C), cyanato (—O—C≡N), fulminato (—C≡N.fwdarw.O), isocyanato (—N═C═O), thiocyanato (—S—C≡N), thiofulminato (—C≡N.fwdarw.S), isothiocyanato (—N═C═S), and dicyano (—N═C═C═N—), ethynyl (—C≡C—) and diethynyl carbodiimido (—N═C═N—) and borodiimido (—N═B—N═.Math.═N—B═N—), nitrido (—N), and halogeno (—F, —Cl, —Br, —I), Lewis bases including at least one of nitrogen derivatives and phosphor derivatives, Lewis acids including at least one of boron derivatives and aluminum derivatives, and transition metal complex anions including M.sup.(I)(CN).sub.6.sup.5−, M.sup.(IIh)(CN).sub.6.sup.4−, M.sup.(IIIh)(CN).sub.6.sup.3−, M(CN).sub.4.sup.2−, and mixtures thereof, wherein M.sup.(I) is Mn, M.sup.(IIh) is selected from the group consisting of Cr, Mn, and Fe, M.sup.(IIIh) is selected from the group consisting of Ti, V, Cr, Mn, Fe, and Co, and M is selected from the group consisting of Ni, Cu, and Zn.

5. The electrochemical energy storage device of claim 1, wherein the covalently functionalized boron nitride nanoparticles comprise being functionalized with at least one of the following: oxo (—O—), peroxo (—O═O—), sulfo (—S—), disulfo (—S—S—), carbonyl (—C≡O), cyano (—C≡N), isocyano (—N≡C), cyanato (—O—C≡N), fulminato (—C≡N.fwdarw.O), isocyanato (—N═C═O), thiocyanato (—S—C≡N), thiofulminato (—C≡N.fwdarw.S), isothiocyanato (—N═C═S), and dicyano (—N═C═C═N—); carbodiimido (—N═C═N—) and borodiimido (—N═B—N═.Math.═N—B═N—); nitrido (—N), and halogeno (—F, —Cl, —Br, —I); Lewis acids including at least one of boron derivatives and aluminum derivatives including at least one of BH.sub.3, BLi.sub.3, BNa.sub.3, B(CH.sub.3).sub.3, BF.sub.3, AlF.sub.3 and BR.sub.1R.sub.2R.sub.3 and AlR.sub.1, R.sub.2R.sub.3 where each of R.sub.1, R.sub.2, and R.sub.3 consists of a halogen selected from the group consisting of F, Cl, Br and I, functionalizing the previously mentioned functional groups creating further functional groups.

6. The electrochemical energy storage device of claim 5, wherein the further functional groups comprise at least one of —C≡N.fwdarw.BF.sub.3, —C≡N.fwdarw.BH.sub.3, and —C≡N.fwdarw.BLi.sub.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a fragment of one example of functionalized hexagonal boron nitride, where the boron and nitrogen atoms are approximately coplanar, while the X and Y functional groups are covalently bound to the boron and nitrogen centers, respectively, above and below the plane of these centers (lines between atoms represent covalent bonds).

(2) FIG. 2 is a schematic view of a first embodiment of an electrochemical energy storage device, showing components: 1—negative electrode current collector; 2—negative electrode that is typically made of lithium, sodium or magnesium foil or from their alloys, graphite intercalated representatives; 3—ionic conductor that allows for the passage of cations released by the negative electrode during discharge or absorbed by the negative electrode during charge, the ionic conductor is an electrical insulator, only a current of positive ions can be transported through it between the positive and negative electrodes, no current of electrons; 4—the positive electrode, an electrically and ionically conductive porous composite matrix that also contains functionalized boron nitride nanoparticles depicted by small lines and numbered as component 6; and 5—the positive electrode current collector, in accordance with implementations of this disclosure. The functionalized boron nitride nanoparticles 6 are embedded in the electrically and ionically conductive porous matrix 4 such that both electrons and ions can be conducted to or from each nano particle simultaneously whereby the functionalized boron nitride nano particles get electrochemically reduced during the discharge of the device or oxidized during the charging of the device thereby allowing for the storage of charge through the valence changes of the atoms in the functionalized boron nitride nanoparticles.

BRIEF DESCRIPTION

(3) An electrochemical energy storage device comprising a positive electrode, a negative electrode and one or more ionic conductors. The positive electrode comprises functionalized boron nitride nanoparticles embedded in a porous electrically and ionically conducting matrix. The negative electrode comprises a material having an electrode potential more negative than that of the positive electrode. The ionic conductors ionically connect the negative and the positive electrodes. The electrochemical energy storage device uses the functionalized boron nitride nanoparticles as electroactive species in that the functionalized boron nitride nanoparticles are electrochemically reduced to enable the release of electrical energy during the discharge of the device. During discharge, the negative electrode releases mobile cations and electrons. The electrons will be conducted to the positive electrode through the wire and load between the electrodes outside the battery, while the cations will be conducted through the ionic conductors to the positive electrode inside the battery. On charge, the flow of the electrons and mobile cations will be reversed. The battery can release electrical energy until the difference of the electrode potentials exists.

(4) The negative electrode comprises a material having an electrode potential more negative than that of the positive electrode. Examples of negative electrode materials include bulk metallic lithium (Li), sodium (Na), potassium (K), beryllium (Be), magnesium (Mg), calcium (Ca), aluminum (Al), their alloys with each other and with other elements, and other forms of these elements, such as their intercalated forms in graphite, graphene, silicon, tin and various crystalline and amorphous materials as part of a composite electrode. The negative electrode may also be made from an electrical double layer on the surface of an electrically conductive material that releases mobile positive ions during discharge, such as quaternary ammonium (NR.sub.1R.sub.2R.sub.3R.sub.4.sup.+) and phosphonium (PR.sub.1R.sub.2R.sub.3R.sub.4.sup.+) cations.

(5) The positive electrode comprises a composite material covering a current collector with good electrical conductivity, such as a metallic mesh. The composite material comprises nanoscopic particles of functionalized boron nitride materials as electroactive species and an electrically and ionically conducting porous matrix embedding the functionalized boron nitride nanoparticles. The composite material further comprises electrolyte and binder materials. The electrically conductive porous matrix may be based on carbon powders, such as graphene flakes, graphite powder, acetylene black and other forms of porous carbon powders. The solid, liquid or polymeric electrolyte provides a polarizable medium for the migration of ions. Examples of electrolyte materials are propylene carbonate, dimethoxyethane and aprotic ionic liquids. One example of suitable binder materials is polyvinylidene fluoride. The electrolyte and binder materials are chosen such that they essentially do not decompose under the voltages applied to the energy storage device during charging and discharging.

(6) The production of such functionalized boron nitride materials is preferably based on the direct reaction of the exfoliated hexagonal boron nitride flakes or boron nitride nanotubes and nanoparticles with salts composed of the above and related cations and the anions of the above mentioned and related functional groups. Examples of such salts involve amides, such as LiNH.sub.2, NaNH.sub.2, KNH.sub.2 and their N-functionalized versions; hydrides (LiH, NaH, KH); metal-organic compounds, such as LiCH.sub.3, NaCH.sub.3, KCH.sub.3, Mg(CH.sub.3).sub.2, Al(CH.sub.3).sub.3, LiC.sub.6H.sub.5; LiCH.sub.3, NaOCH.sub.3, KOCH.sub.3, Mg(OCH.sub.3).sub.2, Al(OCH.sub.3).sub.3, LiOC.sub.6H.sub.5; nitrides, such as Li.sub.3N, Na.sub.3N, K.sub.3N, Be.sub.3N.sub.2, Mg.sub.3N.sub.2, Sr.sub.3N.sub.2, Ba.sub.3N.sub.2, AlN, or Li.sub.3BN.sub.2; nitrates, such as LiNO.sub.3, NaNO.sub.3, KNO.sub.3, Be(NO.sub.3).sub.2, Mg(NO.sub.3).sub.2, Ca(NO.sub.3).sub.2, Al(NO.sub.3).sub.3; hydroxides, such as LiOH, NaOH, KOH, Be(OH).sub.2, Mg(OH).sub.2, Ca(OH).sub.2; carbonates, such as Li.sub.2CO.sub.3, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, BeCO.sub.3, MgCO.sub.3, CaCO.sub.3; fluorides, such as LiF, NaF, KF, BeF.sub.2, MgF.sub.2, CaF.sub.2; Lewis acids and bases, such as NF.sub.3, PF.sub.3, AlF.sub.3 and BF.sub.3 and their analogues with other halogen elements and organic functional groups, such as for example BCl.sub.3, BBr.sub.3, B(CH.sub.3).sub.3; cyanides, such as LiCN, NaCN, KCN, Be(CN).sub.2, Mg(CN).sub.2, Ca(CN).sub.2, Al(CN).sub.3; cianates, such as LiO—C≡N, NaO—C≡N, KO—C≡N, Be(O—C≡N).sub.2, Mg(O—C≡N).sub.2, Ca(O—C≡N).sub.2, Al(O—C≡N).sub.3; fulminates, such as LiC≡N.fwdarw.O, NaC≡N.fwdarw.O, KC≡N.fwdarw.O, Be(C≡N.fwdarw.O).sub.2, Mg(C≡N.fwdarw.O).sub.2, Ca(C≡N.fwdarw.O).sub.2, Al(C≡N.fwdarw.O).sub.3; isocyanates LiN═C═O, NaN═C═O, KN═C═O, Be(N═C═O).sub.2, Mg(N═C═O).sub.2, Ca(N═C═O).sub.2, Al(N═C═O).sub.3; thiocianates, such as LiS—C≡N, NaS—C≡N, KS—C≡N, Be(S—C≡N).sub.2, Mg(S—C≡N).sub.2, Ca(S—C≡N).sub.2, Al(S—C≡N).sub.3; thiofulminates, such as LiC≡N.fwdarw.S, NaC≡N.fwdarw.S, KC≡N.fwdarw.S, Be(C≡N.fwdarw.S).sub.2, Mg(C≡N.fwdarw.S).sub.2, Ca(C≡N.fwdarw.S).sub.2, Al(C≡N.fwdarw.S).sub.3; isothiocyanates LiN═C═S, NaN═C═S, KN═C═S, Be(N═C═S).sub.2, Mg(N═C═S).sub.2, Ca(N═C═S).sub.2, Al(N═C═S).sub.3; salts of Li.sup.+, Na.sup.+, Be.sup.+, Mg.sup.2+, Ca.sup.2+, Al.sup.3+ and quaternary ammonium and phosphonium cations with transition metal complex anions, such as M.sup.(I)(CN).sub.6.sup.5− with M.sup.(I)=Mn, M.sup.(IIh)(CN).sub.6.sup.4− with M.sup.(IIh)=Cr, Mn, Fe, M.sup.(IIIh)(CN).sub.6.sup.3− with M.sup.(IIIh)=Ti, V, Cr, Mn, Fe and Co, M(CN).sub.4.sup.2− with M.sup.(II)=Ni, Cu and Zn, and Cu(CN).sub.2.sup.−. In these reactions, the reduced form of the functionalized boron nitride materials is often produced representing the state of these materials in the discharged batteries. The charging of the battery will produce the oxidized form of the corresponding functionalized boron nitride particles in the positive electrode.

(7) Boron nitride (BN) has several phases. Hexagonal boron nitride is produced in large quantities by the industry and is an economically available material. Its exfoliated version consisting of monolayers or a few layers is also economically available. The production of boron nitride nanotubes, cubic and amorphous boron nitride is also discussed in numerous scientific publications and patents. A few representative technologies related to the production and exfoliation of the various phases of boron nitride are the following: Albert Bable et al., “Preparation of hexagonal boron nitride”, U.S. Pat. No. 3,473,894; K. Imai et al., “Method for producing hexagonal boron nitride and hexagonal boron nitride”, U.S. Pat. No. 7,815,733; J. W. Connell, Y. Lin, “Method for exfoliation of hexagonal boron nitride”, U.S. Pat. No. 8,303,922; S. S. Vagarali, “Method for Producing Cubic Boron Nitride Using Melamine as a Catalyst”, U.S. Pat. No. 5,869,015; K. Jordan et al., “Boron Nitride Nanotubes”, U.S. Pat. No. 8,206,674. These references are incorporated by reference.

(8) Hexagonal boron nitride monolayers share the planar honeycomb structure of graphene, with boron and nitrogen atoms alternating in the vortices of the honeycomb structure.

(9) The functionalized boron nitride material may be composed from any possible phases of boron nitride, such as hexagonal boron nitride, boron nitride nanotubes, cubic boron nitride or amorphous boron nitride. The boron nitride particles made of these boron nitride materials are preferably composed of flakes of ultrathin or monolayer hexagonal boron nitride, boron nitride nanotubes or other nanoscopic particles of the boron nitride material. Some or all of the boron and/or the nitrogen atoms on the surface of these boron nitride particles are covalently functionalized, whereby the resulting functionalized material may possess high electron attachment energy, i.e., it releases energy when it absorbs an electron. Such functionalized boron nitride materials are well suitable for application as positive electrode electroactive species. In certain cases, the functionalization of boron nitride may also lead to an increased electron donor character with a reduced electron attachment energy as compared to non-functionalized boron nitride. In such a case, the functionalized boron nitride material may preferentially be used as a negative electrode electroactive species. Any phases of such functionalized boron nitride materials obtained by varying the pressure, temperature or by any other synthesis routes are also understood here as functionalized boron nitride materials. For example the compound with the stoichiometry of Li.sub.3BN.sub.2 obtainable from boron nitride as dissolved and functionalized in molten Li.sub.3N and, then, annealed is also understood here as functionalized boron nitride.

(10) Materials analogous to Li.sub.3BN.sub.2 with a stoichiometry xA.sub.3N.y(MN) or xAe.sub.3N.sub.2.y(MN) are also considered functionalized boron nitride, for the same reason as Li.sub.3BN.sub.2, x and y are positive nonzero real numbers defining the ratio of components A.sub.3N, (MN) and Ae.sub.3N.sub.2, where A represents alkali metals (A=Li, Na, K), Ae represents alkaline earth metals (Ae=Be, Mg, Ca) and MN represents boron nitride or aluminum nitride. In the A.sub.3N.y(MN) or xAe.sub.3N.sub.2.y(MN) compounds the individual components chemically mix with each other and form new compounds or composite materials. An important example of this class of materials is Li.sub.3AlN.sub.2 and Na.sub.3AlN.sub.2. These materials can often be synthesized by melting together the individual nitride components and annealing the melt.

(11) For positive electrode application, the guiding principle for the choice of functionalization should be that the functionalization of the boron nitride particles increases the electron affinity of the particles, i.e., it strengthens their electron accepting ability. In yet other words, the functionalization leads to increased electron attachment energy, meaning that increased amount of energy is released when electrons attach to such functionalized particles, as compared to non-functionalized boron nitride. Functional groups with electron withdrawing character can induce large positive partial charges in the boron and nitrogen centers of boron nitride, making the functionalized system a strong electron acceptor and a good positive electrode electroactive species, and this will lead to high voltage and high energy density batteries. The following functional groups, primarily functionalizing the boron centers, are especially well suited for this purpose: —F, —C≡N, —N≡C, —O—C≡N, —N═C═O, —S—C≡N, —N═C═S, —N═C═C═N—, —N═C═N—, —N═B—N═ .Math.═N—B═N—, —O, —N; NF.sub.3, PF.sub.3, oxidized forms of Fe(CN).sub.6.sup.4−, Mn(CN).sub.6.sup.4− and other transition metal complexes, also derivatives of the phenyl group containing electron withdrawing functional groups, such as for example cyano (—C≡N) functionalized benzene derivatives. Examples of functional groups that primarily functionalize the N centers and lead to increased electron attachment energy are Lewis acids, such as BF.sub.3, BCl.sub.3 and B(CH.sub.3).sub.3.

(12) The reactions of the salts mentioned above with boron nitride to produce functionalized boron nitrides may be carried out in the melts/liquid phases of the salts or in suitable solvents, such as aqueous solutions or aprotic organic solvents, the latter including ionic liquids and other polar organic solvents. The anions of the salts are initially either physisorbed or chemisorbed primarily to the boron centers of the surface. After the charging of the battery the anions become oxidized and covalently bound to the surface of the boron nitride particle.

(13) Examples of covalent functionalization of the boron and nitrogen centers of the boron nitride nanoparticles include alkyl groups, such as methyl (—CH.sub.3), ethyl (—CH.sub.2—CH.sub.3), propyl (—(CH.sub.2).sub.2—CH.sub.3), butyl (—(CH.sub.2).sub.3—CH.sub.3), isopropyl (—CH(CH.sub.3).sub.2), isobutyl (—CH.sub.2—CH(CH.sub.3).sub.2), tertiary butyl (—C(CH.sub.3).sub.3); phenyl (—C.sub.6H.sub.5) and substituted phenyl, alkoxy groups, such as methoxy (—O—CH.sub.3), ethoxy (—O—CH.sub.2—CH.sub.3), propoxy (—O—(CH.sub.2).sub.2—CH.sub.3), butoxy (—O—(CH.sub.2).sub.3—CH.sub.3); amino (—NH.sub.2) and N-functionalized amino (—NR.sub.1R.sub.2) groups; hydroxyl (—OH), oxo (—O), peroxo (—O═O—), sulfo (—S), disulfo (—S—S—), nitrozo (—N═O), carbonyl (—C≡O), cyano (—C≡N), isocyano (—N≡C), cyanato (—O—C≡N), fulminato (—C≡N.fwdarw.O), isocyanato (—N═C═O), thiocyanato (—S—C≡N), thiofulminato (—C≡N.fwdarw.S), isothiocyanato (—N═C═S), dicyano (—N═C═C═N—), ethynyl (—C≡C—), diethynyl (—C≡C—C≡C—), carbodiimido (—N═C═N—), borodiimido (—N═B—N=.Math.═N—B═N—), hydro (—H) groups; nitrido (—N); halogeno (—F, —Cl, —Br, —I); boron, aluminum, nitrogen and phosphor derivatives acting as Lewis bases (functionalizing the boron centers, such as NF.sub.3 or PF.sub.3), or Lewis acids (functionalizing the nitrogen centers, such as BF.sub.3 or AlF.sub.3); functional groups derived from transition metal complex anions, such as from the oxidized forms of ferrocyanide (Fe(CN).sub.6.sup.4−) and ferricyanide (Fe(CN).sub.6.sup.3−) ions and analogues. A mixture of functionalization or functional groups binding to multiple sites on the same boron nitride surface at the same time, such as for example N(—CH.sub.2—CH—).sub.3, are also allowed. Also note that the smallest functionalized boron nitride particles include borazine (N.sub.3B.sub.3H.sub.6) and ammonia borane (NBH.sub.6) and their functionalized and H-substituted versions. One possible functionalization of hexagonal boron nitride is shown in FIG. 1.

(14) Both the boron and nitrogen centers of boron nitride may be functionalized to increase the energy density and the capacity of the battery. For example, halogen elements (F, Cl, Br, I) can be used for the functionalization of both centers. Lewis acids, such as BF.sub.3, BCl.sub.3, BBr.sub.3, B(CH.sub.3).sub.3, AlF.sub.3, AlCl.sub.3, AlBr.sub.3, Al(CH.sub.3).sub.3, will functionalize the N centers of boron nitride nanoparticles, while Lewis bases, such as NF.sub.3, PF.sub.3 and their other halogenated versions functionalize the B centers. Anions of salts will primarily functionalize the boron centers.

(15) Theoretical studies on the functionalization of boron nitride particles indicate strong covalent binding between the boron atoms and the functional groups. Chemisorption binding energies are typically in the 1.5-6.0 eV range as described in “Band gap engineering by functionalization of BN sheet”, by A. Bhattacharya, S. Bhattacharya and G. P. Das, in Physical Review B 85, 035415 (2012), hereby fully incorporated by reference. Functionalization of boron nitride with organic peroxides and hydroxyl group as described in “Chemically Activated Boron Nitride Nanotubes”, by C. Y. Zhi et al., Chemistry An Asian Journal, 4, 1536, (2009) and in “Oxygen Radical Functionalization of Boron Nitride Nanosheets” by Toby Sainsbury et al., Journal of The American Chemical Society, 134, 18758, (2012) and functionalization with fluorine as described in “Fluorination and Electrical Conductivity of BN Nanotubes” by C. Tang et al., Journal of the American Chemical Society, Communications, 127, 6552 (2005) and in “Excellent electrical conductivity of the exfoliated and fluorinated hexagonal boron nitride nanosheets” by Y. Xue et al., Nanoscale Research Letters 8, 49 (2013) have also been carried out experimentally. These publications are hereby fully incorporated by reference. These references, however, lack teaching the use of these materials for electrochemical energy storage devices.

(16) Also note that the boron atoms in the hexagonal boron nitride flakes can be functionalized from either one or the other side of the planar structure. Boron nitride particles may also get interconnected when functionalized with groups that can bind to more than one boron atoms. Some functionalizations may result in the substitution of B or N atoms of the boron nitride particles. Such functionalizations may still be useful for applications as electroactive materials as they may still serve the purpose of allowing for high electron attachment energies of the boron nitride particles.

(17) The principles described above can also be applied to graphene materials that are doped with boron, nitrogen, aluminum, phosphorus or other main group III or IV atoms and, thus, allow for similar functionalization. The doping means substitution of a fraction of atoms in graphene or boron nitride by atoms other than C for graphene and other than B or N for boron nitride. Even though such materials have already been synthesized, nothing is known of their functionalized forms yet. A review of such materials can be found in “Synthesis Of Nitrogen-Doped Graphene Films For Lithium Battery Application”, by A. L. M. Reddy et al., ACS Nano, 4, 6337 (2010), which is hereby fully incorporated by reference. Furthermore, doping graphene or boron nitride with transition metal elements, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, also leads to increased ability for functionalization, and thus, the functionalized forms of these materials can also be used as electroactive species in positive electrodes of electrochemical energy storage devices.

(18) Charge and discharge rates are significantly higher in many of these functionalized boron nitride materials than for typical three-dimensional Li-ion intercalation materials, since the Li ions (or other cations) have to intercalate into functionalized two-dimensional surfaces only, instead of intercalating inside nanoscopic crystals. Gravimetric and volumetric energy densities, as well as capacities of the boron nitride based devices, are similar to those of Li ion batteries when the surfaces of the boron nitride nanoparticles are functionalized densely and with functional groups that promote high voltage (high electron attachment energy) and high capacity.

(19) Examples of functionalized boron nitride particles and their calculated properties are provided below. More specifically, the reduced (discharged) and oxidized (charged) forms of positive electrode materials are presented here along with their electronic energies as calculated using the Quantum Espresso (version 5.0.2, svn revision 9656) suit of electronic structure codes. The voltage of the corresponding batteries is also calculated and presented here as the electronic energy change during the cell reaction, as expressed in units of electron volts divided by the number of electrons transferred during the reaction. The Quantum Espresso suite of programs is described in P. Giannozzi, et. al (2009), “QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials”, Journal of Physics: Condensed Matter, 39, 395502; www.quantum-espresso.org. A wavefunction cut-off of 50-80 rydbergs has been applied, in combination with PBEsol exchange-correlation functionals implemented with ultrasoft pseudopotentials as provided with Quantum Espresso. The density of the k-space gridpoints was gradually increased until structures and energies converged, typically a k-space grid density of 2×2×2 (for 3D crystals) or a 2×2×1 (for monolayer slabs) is sufficient for electrochemical accuracy, but convergence of structural relaxations and energies were checked beyond this k-space density as well. Residual forces on converged atomic positions were smaller than 0.0001 Rydberg/bohr, residual pressure on the converged simulation cell was smaller than 1 kbar, electronic energies were converged to 0.01 microRydbergs. The electronic energies obtained for the relaxed structures were used as approximate enthalpies to calculate reaction enthalpies of the electrochemical cell reactions and the corresponding voltages and energy densities. These calculations are meant to be a guidance to obtain good estimates of the stability and structure, as well as the energetics and voltage of the electroactive species in the cell reactions. The voltages are in reference to the corresponding bulk metal electrodes.

Example 1: α-Li.SUB.3.BN.SUB.2

(20) Cell reaction for discharge: 4Li+2LiBN2.fwdarw.2Li.sub.3BN.sub.2

(21) Electronic energies: E(2Li.sub.3BN.sub.2)=−182.229491 Ry; E(2LiBN.sub.2)=−122.243727 Ry; E(2×2Li)=−58.92329074 Ry.

(22) Cell reaction energy:

(23) ΔE=E(2Li.sub.3BN.sub.2)-E(2LiBN.sub.2)-E(2×2Li)=−1.062387 Ry=−14.453782 eV.

(24) Cell voltage: U=−ΔE/4 electrons=3.613 V.

(25) Mass-density: ρ.sub.M(Li.sub.3BN.sub.2)=1.823 kg/L.

(26) Gravimetric energy density: ρ.sub.EG(Li.sub.3BN.sub.2)=−ΔE/(6M(Li)+2M(B)+4M(N))=3247 Wh/kg.

(27) Volumetric energy density: ρ.sub.EV(Li.sub.3BN.sub.2)=5919 Wh/L.

(28) Gravimetric capacity density: ρ.sub.CG(Li.sub.3BN.sub.2)=899 mAh/g.

(29) Volumetric capacity density: ρ.sub.CV(Li.sub.3BN.sub.2)=1638 mAh/cm.sup.3.

Example 2: BNCNNa

(30) In this example, the hexagonal boron nitride monolayer is functionalized by cyano groups on the boron atoms, on both sides of the monolayer, with a single cyano group attached to each boron atom. An approximately 30 Å wide vacuum layer separates the functionalized monolayers, while 3D periodic boundary conditions are applied.

(31) Cell reaction for discharge: 2Na+2BNCN.fwdarw.2BNCNNa

(32) Electronic energies: E(2BNCNNa)=−301.33420522 Ry; E(2BNCN)=−116.69635186 Ry; E(2Na)=−184.21607496 Ry.

(33) Cell reaction energy: ΔE=E(2BNCNNa)-E(2BNCN)-E(2Na)=−0.42177839 Ry=−5.73829505 eV.

(34) Cell voltage: U=−ΔE/2 electrons=2.87 V.

(35) Mass-density: ρ.sub.M(BNCNNa)≈3.406 kg/L.

(36) Gravimetric energy density: ρ.sub.EG(BNCNNa)=−ΔE /(2M(Na)+2M(B)+4M(N)+2M(C))=1042 Wh/kg.

(37) Volumetric energy density: ρ.sub.EV(BNCNNa)=3547 Wh/L.

(38) Gravimetric capacity density: ρ.sub.CG(BNCNNa)=363 mAh/g.

(39) Volumetric capacity density: ρ.sub.CV(BNCNNa)=1236 mAh/cm.sup.3.

Example 3: BNNBNLi.SUB.3

(40) In this example, the hexagonal boron nitride monolayer is functionalized by borodiimido groups on the boron atoms, on both sides of the monolayer, with a single borodiimido group attached to each boron atom of the hexagonal boron nitride monolayer. An approximately 30 Å wide vacuum layer separates the functionalized monolayers, while 3D periodic boundary conditions are applied.

(41) Cell reaction for discharge: 6Li+2BNNBN.fwdarw.2BNNBNLi.sub.3

(42) Electronic energies: E(2BNNBNLi.sub.3)=−235.1329642302 Ry; E(2BNNBN)=−145.91847540 Ry; E(2Li)=−29.46164537 Ry.

(43) Cell reaction energy: ΔE=E(2BNNBNLi.sub.3)-E(2BNNBN)-3E(2Li)=−0.82955272 Ry=−11.28606475 eV.

(44) Cell voltage: U=−ΔE/6 electrons=1.88 V.

(45) Mass-density: ρ.sub.M(BNNBNLi.sub.3)≈2.263 kg/L.

(46) Gravimetric energy density: ρ.sub.EG(BNNBNLi.sub.3)=−ΔE /(6M(Li)+4M(B)+6M(N))=1790 Wh/kg.

(47) Volumetric energy density: ρ.sub.EV(BNNBNLi.sub.3)=4050 Wh/L.

(48) Gravimetric capacity density: ρ.sub.CG(BNNBNLi.sub.3)=952 mAh/g.

(49) Volumetric capacity density: ρ.sub.CV(BNNBNLi.sub.3)=2154 mAh/cm.sup.3.

Example 4: BNNCNLi.SUB.2

(50) In this example, the hexagonal boron nitride monolayer is functionalized by carbodiimido groups on the boron atoms, on both sides of the monolayer, with a single carbodiimido group attached to each boron atom of the hexagonal boron nitride monolayer. An approximately 30 Å wide vacuum layer separates the functionalized monolayers, while 3D periodic boundary conditions are applied.

(51) Cell reaction for discharge: 4Li+2BNNCN.fwdarw.2BNNCNLi.sub.2

(52) Electronic energies: E(2BNNCNLi.sub.2)=−216.6704818572 Ry; E(2BNNCN)=−157.05154280 Ry; E(2Li)=−29.46164537 Ry.

(53) Cell reaction energy: ΔE=E(2BNNCNLi.sub.2)-E(2BNNCN)-2E(2Li)=−0.69564831 Ry=−9.46429535 eV.

(54) Cell voltage: U=−ΔE/4 electrons=2.366 V.

(55) Mass-density: ρ.sub.M(BNNCNLi.sub.2)≈2.949 kg/L.

(56) Gravimetric energy density: ρ.sub.EG(BNNCNLi.sub.2)=−ΔE/(4M(Li)+2M(B)+6M(N)+2M(C))=1611 Wh/kg.

(57) Volumetric energy density: ρ.sub.EV(BNNCNLi.sub.2)=4751 Wh/L.

(58) Gravimetric capacity density: ρ.sub.CG(BNNCNLi.sub.2)=680 mAh/g.

(59) Volumetric capacity density: ρ.sub.CV(BNNCNLi.sub.2)=2008 mAh/cm.sup.3.

Example 5: AlN(BN).SUB.2

(60) In this example, hexagonal boron nitride monolayers are linked through N atoms and form a multilayer sandwich structure with channels for intercalating cations, such as Al.sup.3+.

(61) Cell reaction for discharge: Al+N(BN).sub.2.fwdarw.AlN(BN).sub.2

(62) Electronic energies: E(2AlN(BN).sub.2)=−157.81487893 Ry; E(2N(BN).sub.2)=−146.22361240 Ry; E(2Al)=−10.90558327 Ry.

(63) Cell reaction energy: ΔE=E(AlN(BN).sub.2)-E(N(BN).sub.2)-E(2Al)=−0.68568326 Ry=−9.3287207523 eV.

(64) Cell voltage: U=−ΔE/6 electrons=1.555 V.

(65) Mass-density: ρ.sub.M(AlN(BN).sub.2)=3.470 kg/L.

(66) Gravimetric energy density: ρ.sub.EG(AlN(BN).sub.2)=−ΔE/(2M(Al)+4M(B)+6M(N))=1379 Wh/kg.

(67) Volumetric energy density: ρ.sub.EV(AlN(BN).sub.2)=4787 Wh/L.

(68) Gravimetric capacity density: ρ.sub.CG(AlN(BN).sub.2)=887 mAh/g.

(69) Volumetric capacity density: ρ.sub.CV(AlN(BN).sub.2)=3079 mAh/cm.sup.3.

Example 6: BNNBNA1

(70) In this example, the hexagonal boron nitride monolayer is functionalized by borodiimido groups on the boron atoms, on both sides of the monolayer, with a single borodiimido group attached to each boron atom of the hexagonal boron nitride monolayer. An approximately 30 Å wide vacuum layer separates the functionalized monolayers, while 3D periodic boundary conditions are applied. Al.sup.3+ cations are the mobile cations.

(71) Cell reaction for discharge: 2Al+2BNNBN.fwdarw.2BNNBNA1

(72) Electronic energies: E(2BNNBNA1)=−157.58583252 Ry; E(2BNNBN)=−145.91847540 Ry; E(2Al)=−10.90558327 Ry.

(73) Cell reaction energy: ΔE=E(2BNNBNA1)-E(2BNNBN)-E(2Al)=−0.76177385 Ry=−10.36393327 eV.

(74) Cell voltage: U=−ΔE/6 electrons=1.72 V.

(75) Mass-density: ρ.sub.M(BNNBNAl)≈4.000 kg/L.

(76) Gravimetric energy density: ρ.sub.EG(BNNBNAl)=−ΔE /(6M(Li)+4M(B)+6M(N))=1532 Wh/kg.

(77) Volumetric energy density: ρ.sub.EV(BNNBNAl)=6130 Wh/L.

(78) Gravimetric capacity density: ρ.sub.CG(BNNBNAl)=887 mAh/g.

(79) Volumetric capacity density: ρ.sub.CV(BNNBNAl)=3549 mAh/cm.sup.3.

(80) The one or more ionic conductors comprise materials allowing for the transport of ions between the positive and the negative electrodes. In one embodiment, the ionic conductor comprises an electrolytic fluid for the positive electrode space and another electrolytic fluid for the negative electrode space separated from each other by an ion selective membrane. The ion selective membrane allows the transport of the cations released by the negative electrode during discharge or absorbed by the negative electrode on charge. The electrolytic fluids are essentially non-reactive to the other battery components, though they may contribute to the formation of electrode-electrolyte interfaces. The electrolytic fluids provide an electrically polarizable medium, usually through molecules with large dipole moments that mediates electrostatic interactions within the battery and promotes the equilibration of positive and negative charges. Such electrolytic fluids may be protic or aprotic depending on the choice of the electroactive species and the rest of the battery. For the negative electrode, space aprotric electrolytes are preferred. Examples of suitable aprotic electrolytic fluids include propylene carbonate, dimethoxyethane and aprotic ionic liquids and their mixtures and dissolved salts that increase the ionic conductivity of the medium but do not participate in electrode reactions. An example of such salts is lithium bis oxalato borate (LiBOB). Similar electrolytic fluids are preferentially applicable to the positive electrode space as well. In another preferred embodiment, the ionic conductors may be based on polymeric macromolecules that provide a similar ionic conductivity as the electrolytic fluids. An example of such polymer is polyvinilidene fluoride. The ion selective membranes in the ionic conductors may be based on polymers, such as the NAFION type membranes, or they may be ceramic materials such as LISICON.

(81) One mode of operation of the electrochemical energy storage devices based on functionalized boron nitride positive electrode electroactive species uses two- or three-atomic functional groups attached to each boron atoms of the boron nitride monolayer or boron nitride nanotube, while the nitrogen atoms of the boron nitride monolayers and nanotubes remain non-functionalized. Each functionalized boron atom of the boron nitride monolayers or nanotubes is functionalized only by a single functional group. The functional groups that are spatial neighbors on the functionalized surfaces may further become interconnected through shared atoms and bonds. Such interconnection may happen after functionalization of the boron nitride surfaces as a consequence of additional reactions between neighboring functional groups. For positive electrode electroactive species, the preferred functional groups functionalizing the boron nitride monolayers and nanotubes are the cyano (—C≡N), isocyano (—N≡C), cyanato (—O—C≡N), fulminato (—C≡N.fwdarw.O), isocyanato (—N═C═O), thiocyanato (—S—C≡N), thiofulminato (—C≡N.fwdarw.S), isothiocyanato (—N═C═S), dicyano (—N═C═C═N—), carbodiimido (—N═C═N—), borodiimido (—N═B—N═.Math.═N—B═N—) groups, as well as their BF.sub.3, AlF.sub.3 and sulfur (—S—) or oligosulfur (—S.sub.n—) adducts. An example of such an adduct forms when BF.sub.3 or sulfur is chemisorbed to the cyano groups of the cyano-functionalized boron nitride monolayers (—C≡N.fwdarw.BF.sub.3 and —C≡N.fwdarw.S). Other preferred embodiments of the positive electrode electroactive species include 3D structures of sulfur (—S—), oligosulfur (—S.sub.n—), oxygen (—O—) or nitrogen (—N—) interconnected boron nitride monolayers. In another preferred embodiment, the electroactive species of the positive electrode are α-Li.sub.3BN.sub.2, Li.sub.3AlN.sub.2 or LiPN.sub.2, which may preferably be doped with Li.sub.2S, LiF, Li.sub.2CN.sub.2, LiNH.sub.2 in a 5-50 mol % amount to increase ionic conductivity and electrochemical stability. Preferred anode materials are bulk lithium, sodium, magnesium and aluminum or their suitable composites and alloys that allow for safe operation of the storage device, such as for example graphite intercalated lithium. Preferred electrolytes are based on glymes, propylene carbonate, ethylene carbonate, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, organic ionic liquids, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, N-methyl-2-pyrrolidone with added dissolved salts of the anode electroactive metal, such as salts with PF.sub.6.sup.−, ClO.sub.4.sup.−, BF.sub.4.sup.−, CF.sub.3SO.sub.3.sup.−, N(CF.sub.3SO.sub.2).sub.2.sup.−, N(C.sub.2F.sub.5SO.sub.2).sub.2.sup.−, C(CF.sub.3SO.sub.2).sub.3.sup.−, C(C.sub.2F.sub.5SO.sub.2).sub.3.sup.− and halogen anions for increased ionic conductivity. In some preferred embodiments, there is no liquid electrolyte as the functionalized boron nitride particles have sufficient ionic conductivity to serve as electroactive species and electrolyte in the same time. Binder materials are preferably based on polyvinylidene-fluoride, acrylonitrile polymers, such as a copolymer of acrylonitrile and methyl methacrylate and a copolymer of acrylonitrile and methyl acrylate; and poly ethylene oxide. Such binder materials may also serve as solid polymer electrolytes eliminating the use of liquid electrolytes. Both electrolytes and binder materials have to be chosen such that they do not react with the electroactive species, or the electroactive species should be protected by surface coating by porous carbon, polymers or porous inorganic materials such as Si.sub.3N.sub.4 or SiS.sub.2, to avoid such unintended reactions. Preferred cation-selective membranes separating the anode and cathode spaces may be based on NAFION type membranes, or ceramic membranes, such as LISICON ones.

(82) It is to be understood that various changes in the details, materials, arrangements of parts and components and methods which have been described and illustrated herein in order to explain the nature of the energy storage devices that may be made by those skilled in the art within the principle and scope of the energy storage devices as expressed in the appended claims. Furthermore, while various features have been described with regard to particular embodiments and methods, it will be appreciated that features described for one embodiment also may be incorporated with the other described embodiments.

(83) All publications and patent documents cited in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication or patent document were so individually denoted.

(84) Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. § 112, ¶6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. § 112, ¶ 6.