A method for transforming a crystal form of an electrolyte containing lithium for aluminum electrolysis includes the following steps: S1, pulverizing the electrolyte containing lithium; S2, uniformly mixing an additive with the electrolyte powder to obtain a mixture, wherein the additive is one or more selected from the group consisting of an oxide of an alkali metal other than lithium, an oxo acid salt of an alkali metal other than lithium, and a halide of an alkali metal other than lithium; a molar ratio of a sum of alkali metal fluoride contained in the electrolyte, alkali metal fluoride directly added from the additive, and alkali metal fluoride to which the additive is converted under the high-temperature calcination condition in the mixture to aluminum fluoride is greater than 3; S3, calcining the mixture at a high temperature.

A method for transforming a crystal form of an electrolyte containing lithium for aluminum electrolysis includes the following steps: S1, pulverizing the electrolyte containing lithium; S2, uniformly mixing an additive with the electrolyte powder to obtain a mixture, wherein the additive is one or more selected from the group consisting of an oxide of an alkali metal other than lithium, an oxo acid salt of an alkali metal other than lithium, and a halide of an alkali metal other than lithium; a molar ratio of a sum of alkali metal fluoride contained in the electrolyte, alkali metal fluoride directly added from the additive, and alkali metal fluoride to which the additive is converted under the high-temperature calcination condition in the mixture to aluminum fluoride is greater than 3; S3, calcining the mixture at a high temperature.

A device comprising a nonlinear optical (NLO) material according to the formula XLi.sub.2Al.sub.4B.sub.6O.sub.20F. A device comprising a nonlinear optical material (NLO) according to the formula KSrCO.sub.3F, wherein the NLO comprises at least one single crystal. A nonlinear optical material selected from the group consisting of KSrCO.sub.3F Rb.sub.3Ba.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F and K.sub.3Sr.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F.

A device comprising a nonlinear optical (NLO) material according to the formula XLi.sub.2Al.sub.4B.sub.6O.sub.20F. A device comprising a nonlinear optical material (NLO) according to the formula KSrCO.sub.3F, wherein the NLO comprises at least one single crystal. A nonlinear optical material selected from the group consisting of KSrCO.sub.3F Rb.sub.3Ba.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F and K.sub.3Sr.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F.

Provided is a fluoride ion secondary battery having a capacity larger than that of a conventional one. The fluoride ion secondary battery includes a negative electrode including Li.sub.3AlF.sub.6 as a negative electrode active material. The content of the active material Li.sub.3AlF.sub.6 in the negative electrode may be 25% by mass or less. The active material Li.sub.3AlF.sub.6 may be in an amorphous state and may be in the form of particles with an average particle size on the order of micrometers.

Disclosed is a process for coating onto a substrate, including preparing a precursor having a general formula Q.sub.m/nMO.sub.xF.sub.y by a reaction M(OH).sub.x+yHF+m/nQ(OH).sub.n.fwdarw.Q.sup.n+.sub.m/n(MO.sub.xF.sub.y).sup.m−, wherein Q is an onium ion, selected from quaternary alkyl ammonium, quaternary alkyl phosphonium and trialkylsulfonium; M is a metal capable of forming an oxofluorometallate, where M may further comprise one or more additional metal, metalloid, and one or more of phosphorus (P), sulfur (S) and selenium (Se), iodine (I), and arsenic (As) or a combination thereof, and x>0, y>0, m≥1, n≥1; combining the precursor with a lithium ion source and with the substrate, and mixing to form a coating composition comprising a lithium oxofluorometallate having a general formula Li.sub.mMO.sub.xF.sub.y on the substrate. Further disclosed is a core-shell electrode active material including a core capable of intercalating and deintercalating lithium coated with the lithium oxofluorometallate having the general formula Li.sub.mMO.sub.xF.sub.y.

Disclosed is a process for coating onto a substrate, including preparing a precursor having a general formula Q.sub.m/nMO.sub.xF.sub.y by a reaction M(OH).sub.x+yHF+m/nQ(OH).sub.n.fwdarw.Q.sup.n+.sub.m/n(MO.sub.xF.sub.y).sup.m−, wherein Q is an onium ion, selected from quaternary alkyl ammonium, quaternary alkyl phosphonium and trialkylsulfonium; M is a metal capable of forming an oxofluorometallate, where M may further comprise one or more additional metal, metalloid, and one or more of phosphorus (P), sulfur (S) and selenium (Se), iodine (I), and arsenic (As) or a combination thereof, and x>0, y>0, m≥1, n≥1; combining the precursor with a lithium ion source and with the substrate, and mixing to form a coating composition comprising a lithium oxofluorometallate having a general formula Li.sub.mMO.sub.xF.sub.y on the substrate. Further disclosed is a core-shell electrode active material including a core capable of intercalating and deintercalating lithium coated with the lithium oxofluorometallate having the general formula Li.sub.mMO.sub.xF.sub.y.

An electrolyte material is represented by Li.sub.4-3a-cbAl.sub.aM.sub.bF.sub.xCl.sub.yBr.sub.4-x-y, wherein M is at least one selected from the group consisting of Mg, Ca, and Zr; c represents a valence of M; and the following five inequalities are satisfied: 0<a<1.33, 0≤b <2, 0<x<4, 0≤y<4, and (x+y)≤4.

A device comprising a nonlinear optical (NLO) material according to the formula XLi.sub.2Al.sub.4B.sub.6O.sub.20F. A device comprising a nonlinear optical material (NLO) according to the formula KSrCO.sub.3F, wherein the NLO comprises at least one single crystal. A nonlinear optical material selected from the group consisting of KSrCO.sub.3F Rb.sub.3Ba.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F and K.sub.3Sr.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F.

A device comprising a nonlinear optical (NLO) material according to the formula XLi.sub.2Al.sub.4B.sub.6O.sub.20F. A device comprising a nonlinear optical material (NLO) according to the formula KSrCO.sub.3F, wherein the NLO comprises at least one single crystal. A nonlinear optical material selected from the group consisting of KSrCO.sub.3F Rb.sub.3Ba.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F and K.sub.3Sr.sub.3Li.sub.2Al.sub.4B.sub.6O.sub.20F.