Cathode of all-solid lithium battery and secondary battery using the same

Abstract

Disclose are a cathode of an all-solid lithium battery, and a secondary battery system using the same. The cathode includes a lithium composite, and a method of manufacturing the lithium composite comprises: dispersing a solid electrolyte to be uniformly distributed in the pores of a mesoporous conductor to provide a solid electrolyte composite, and coating the solid electrolyte composite on the surface of a lithium compound including nonmetallic solids such as S, Se, and Te.

Claims

1. A method for manufacturing a cathode of an all-solid lithium battery, comprising: dispersing a solid electrolyte in pores of a mesoporous conductor to provide a solid electrolyte composite; preparing a lithium composite by coating the solid electrolyte composite on a surface of a lithium compound particle; and connecting a plurality of the lithium composites using a binder, wherein the lithium compound is an active material of the cathode, and the mesoporous conductor comprises a metallic element and a carbon material such that the mesoporous conductor has an electric resistance value of about 10.sup.−6 Ω.Math.m or less.

2. The method of claim 1, wherein the lithium compound is represented as Li.sub.2X, wherein the X comprises at least one selected from the group consisting of S, Se, and Te.

3. The method of claim 1, wherein the solid electrolyte is uniformly distributed in the pores of the mesoporous conductor.

4. The method of claim 1, the method further comprising, coating a slurry of the lithium composite connected by the binder on a cathode collector, and then, rolling the coated slurry.

5. The method of claim 1, wherein a size of the mesoporous conductor is from about 10 nm to about 100 μm, a porosity of the mesoporous conductor is from about 10 to about 90 vol %, and a size of the pores of the mesoporous conductor is from about 2 nm to about 50 nm.

6. The method of claim 1, wherein the solid electrolyte is a material in a two-phase or more including a Li element, and the solid electrolyte comprises one or more selected from the group consisting of oxide-based solid electrolyte including lithium oxide and sulfur-based solid electrolyte including lithium sulfur.

7. The method of claim 1, wherein the solid electrolyte is dispersed in the pores of the mesoporous conductor by a melting-diffusion method, a infiltration method, or a gas-solid mixing method.

8. The method of claim 1, wherein the solid electrolyte is uniformly distributed in the pores of the mesoporous conductor, by preparing a solid electrolyte solution by dispersing the solid electrolyte in a solvent, mixing the solid electrolyte solution with the mesoporous conductor, and evaporating the solvent.

9. The method of claim 1, wherein the coating of the solid electrolyte composite is performed by a dry ball milling, a dry planetary milling, mechanofusion, a wet ball milling, or a wet planetary milling.

10. The method of claim 1, wherein the binder comprises one or more selected from the group consisting of a fluorine-based binder and a rubber-based binder.

11. The method of claim 4, wherein the slurry is coated by a slip casting, pressure casting, tape casting, or gel casting method.

12. The method of claim 4, wherein the rolling is performed by a compaction, a roll press, or an isostatic compaction, and the rolling is performed under the condition of a compression ratio of about 20 to 50%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein:

(2) FIG. 1 illustrates a chemical mechanism in a conventional all-solid lithium battery;

(3) FIG. 2 illustrates an exemplary cathode and active materials thereof in an exemplary all-solid lithium battery according to an exemplary embodiment of the present invention;

(4) FIG. 3 illustrates an exemplary battery system using an exemplary cathode according to an exemplary embodiment of the present invention; and

(5) FIG. 4 shows exemplary experimental results of measuring the discharge capacities and voltages of an exemplar battery including an exemplary all-solid complex cathode according to an exemplary embodiment of the present invention and a conventional battery including a conventional cathode in the related arts.

(6) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

(7) In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

(8) Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

(9) The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

(10) Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”

(11) FIG. 1 illustrates a conventional technique of a lithium sulfur battery. During discharging, the electron migrated from a lithium anode is bound to a sulfur particle adjacent to the surface of a conductor, and then, the sulfur particle is reduced into S.sub.8.sup.2− and dissolved in liquid electrolyte. The S.sub.8.sup.2− is bound to a lithium ion to form Li.sub.2S.sub.8 (long-chain polysulfide) as being dissolved in electrolyte. The Li.sub.2S.sub.8 is consistently subjected to a reduction reaction with a Li ion, and finally, is precipitated on the surface of the lithium anode in a type of Li.sub.2S.sub.2—Li.sub.2S (short-chain polysulfide). Meanwhile, during charging, due to an oxidation reaction, the precipitated polysulfide turns into S.sub.8.sup.2− through a reverse process, and the electron is lost, such that the sulfur particle is precipitated on the surface of the conductor. However, as illustrated in drawings, at the time of being charged, during the oxidation process from Li.sub.2S.sub.2—Li.sub.2S into Li.sub.2S.sub.8, a polysulfide shuttle phenomenon may occur as reacting with a lithium ion and producing Li.sub.2S.sub.2—Li.sub.2S again. Such a shuttle phenomenon may occur in a lithium sulfur battery that uses a liquid electrolyte, and further may cause self-discharge continuously during the charging, which may be one of the greatest problem occurring in a liquid electrolyte system. Therefore, a battery life may be reduced, and the efficiency of active material mass at the time of being discharged may be reduced. In order to solve the conventional problems, according to the present technique, a solid electrolyte complex may be formed to solve the above problems.

(12) Thus, in one aspect, the present invention provides a method for manufacturing a cathode of an all-solid lithium battery. The method may comprise:

(13) dispersing a solid electrolyte in pores of a mesoporous conductor to provide a solid electrolyte composite;

(14) preparing a lithium composite by coating the solid electrolyte composite on a surface of a lithium compound particle; and

(15) connecting a plurality of the lithium composites using a binder.

(16) Alternatively, the method may comprise:

(17) providing a solid electrolyte;

(18) preparing a solid electrolyte composite by dispersing the solid electrolyte in the pores of a mesoporous conductor;

(19) preparing a lithium composite by coating the solid electrolyte composite on a surface of a lithium compound particle; and

(20) connecting a plurality of the lithium composites using a binder.

(21) Preferably, in the solid electrolyte composite, the solid electrolyte may be uniformly dispersed in the pores of the mesoporous conductor.

(22) In a preferred embodiment, the lithium compound particle as the active material of the cathode may be represented by Li.sub.2X and X may be at least one selected from the group consisting of S, Se, and Te. Particularly, the Li.sub.2X particles may be formed by aggregating or binding each Li.sub.2X molecules, in a shape of sphere, oval or other polyhedrons, however, without any limitations in shapes.

(23) Preferably, the Li.sub.2X particle may suitably have a size ranging from about 10 nm to about 100 μm, from about 100 nm to about 5 μm.

(24) FIG. 2 illustrates an exemplary cathode structure of the all-solid lithium battery according to an exemplary embodiment of the present invention, and an exemplary method for manufacturing the same.

(25) First, a mesoporous conductor (ordered mesoporous conductor, OMC) and the solid electrolyte may be provided and a solid electrolyte composite may be prepared by dispersing the synthesized solid electrolyte (SE) in the pores of a mesoporous conductor. In particular, the solid electrolyte may be uniformly distributed throughout the pores of the mesoporous conductor.

(26) Subsequently, the solid electrolyte composite may be coated on the surface of a lithium compound or a lithium compound particle to form a lithium composite. Preferably, the lithium compound may be represented as Li.sub.2X. The lithium particles of Li.sub.2X may include at least one element of nonmetallic solid, such as S, Se, and Te. In particular, the nonmetallic solid material may be selected from Group 6 elements in the periodic table.

(27) Further, in order to prepare an electrode, the prepared lithium composites may be connected each other using a binder such as an organic binder, and then, may be treated with a rolling to provide sufficient ion conduction and electron transport.

(28) FIG. 3 illustrates an exemplary manufacturing method and an exemplary cathode structure of an exemplary all-solid lithium battery according to an exemplary embodiment of the present invention.

(29) For example, a slurry comprising the lithium composite may be coated on the surface of a cathode collector, and then, the coated slurry may be treated with rolling. A solid electrolyte of the battery may be laminated on the cathode surface in a form of a thin film, and then, as a counter electrode, an anode comprising lithium and silicone may be connected on the surface of an anode collector to manufacture a type of mono cell.

(30) An operation principle of the battery system is as follows. At the time of being discharged, Li.sub.2X (X: S, Se, Te), a cathode active material, loses electron, and then, an oxidation reaction may occur as follows:
Li.sub.2X(s).fwdarw.2Li.sup.++X(s)+2e

(31) As such, a lithium ion can move to the side of an anode and X may be formed in a solid phase on the surface of a cathode. At the time of being charged, the lithium is oxidized on the surface of an anode, and then, moved to the side of a cathode; and in the cathode, the reduction reaction may occur to form Li.sub.2X as follows.
X(s)+2Li.sup.++2e.sup.−.fwdarw.Li.sub.2X(s),

(32) As discussed above, the Li.sub.2X of the present invention is used as an active material of a cathode.

(33) Preferably, the mesoporous conductor may have an electric resistance value of about 10.sup.−6 Ω.Math.m or less, and may include a metallic element and carbon. Preferably, the size of the mesoporous conductor may range from several nm to 100 μm, and the porosity thereof may be from about 10 to about 90 vol %. In addition, a size of pores may range from about 2 nm to about 50 nm or less such that is the pores may be affected by capillary force when dispersing the solid electrolyte in the pores.

(34) The solid electrolyte may be one or more selected from the group consisting of oxide-based solid electrolyte and sulfur-based solid electrolyte. Exemplary oxide-based solid electrolyte may be, not limited to, a lithium oxide that may exist in a two-phase or more, and exemplary sulfur-based solid electrolyte may be, but not limited to lithium sulfur.

(35) In a preferred aspect, when the solid electrolyte is dispersed in the mesoporous conductor, the dispersing may be performed by a melting-diffusion method, an infiltration method, or a gas-solid mixing method. For example, the melting-diffusion method may include: changing the solid electrolyte to a liquid phase having fluidity by applying heat to the solid electrolyte, and then, injecting the solid electrolyte inside the mesopores of the conductor. The gas-solid mixing method may include: including evaporating the solid electrolyte, and then, depositing the solid electrolyte in a solid phase inside the mesopores of the conductor.

(36) Further, the solid electrolyte composite may be coated by a mechanical drying and/or wet mixing. Exemplary mechanical dry mixing may be a ball milling, a planetary milling, or a mechanofusion, and exemplary mechanical wet mixing may be a ball milling or planetary milling using a solvent that does not generate the side reactions between the conductor and solid electrolyte.

(37) Preferably, the thus prepared lithium composite may suitably have a size ranging from about 100 nm to about 100 μm, or from about 1 μm to about 10 μm.

(38) The binder may comprise one or more selected from the group consisting of a fluorine-based binder and a rubber-based binder.

(39) Meanwhile, when the slurry comprising the lithium composite is coated on a cathode collector, a rolling may be performed, and then, the coating may be performed by a slip casting, pressure casting, tape casting, or gel casting method. Preferably, the rolling may be performed under the condition of the compression ratio of about 20 to 50% by a compaction, roll press, isostatic compaction, and the like.

(40) The present invention has remarkable advantages as compared with the conventional techniques as follows.

(41) 1) The life span of the battery may be improved is excellent because the shuttle phenomenon of an active material may be prevented as compared with the conventional liquid electrolyte system.

(42) 2) The stability of the battery may be improved at a high temperature as compared with the case of using liquid electrolyte.

(43) 3) Since liquid electrolyte is not used, a secondary battery having high energy density may be obtained as compared with the conventional technique.

(44) 4) By using an active material in a type of Li.sub.2X as a cathode active material, sufficient space may be maintained even when the volume of X is expanded during a reduction reaction.

Examples

(45) Hereinafter, the present invention will be described in more detail with reference to the following embodiments. However, the embodiments are only for illustrating the present invention, and the present invention is not limited thereto.

Example

(46) 1. Manufacturing of OMC/SE Complex

(47) Li.sub.2S powder and P.sub.2S.sub.5 were mixed in a ratio of 80:20 wt %; the mixture thus obtained was milled at 500 rpm for 8 hours; and then, the mixture thus obtained was subjected to a thermal treatment at 200° C. The prepared Li.sub.2S/P.sub.2S.sub.5 (LSPS) powder was added in an N-methylformamide (NMF) solvent; the LSPS powder was dissolved to be a state of super-saturation; the ordered mesoporous conductor (OMC) powder was dispersed into a LSPS solution; the OMC powder was subjected to a vacuum thermal treatment at 150° C. for 3 hours; and then, the solvent was removed to manufacture an OMC/SE complex.

(48) 2. Manufacturing of OMC/SE/Li.sub.2S Complex

(49) The OMC/SE complex and Li.sub.2S powder were mixed in a mass ratio of 6:4; and then, the mixture thus obtained was subjected to a planetary milling at 300 rpm for 3 hours to manufacture a OMC/SE/Li.sub.2S complex.

(50) 3. Manufacturing of all-solid complex cathode

(51) The above-prepared OMC/SE/Li.sub.2S powder, a rubber-based binder, and a BTX (benzene, toluene, and the three xylene isomers)-based solvent were mixed to prepare cathode slurry. The cathode slurry was coated on the surface of a substrate; and then, the solvent was removed through a convective drying at 80° C. for 8 hours to manufacture an all-solid complex cathode.

(52) For the all-solid complex cathode thus obtained and the conventional cathode, the discharge capacities and voltages were measured. The results thus obtained are illustrated in FIG. 4.

(53) The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.