KR101352791B1 - Structure for ionic conductive way of electrolyte membrane in lithium ion secondary battery - Google Patents

Abstract

The present invention relates to a protective structure for ion conductive channel of an electrolyte membrane in a lithium-ion secondary battery and, more particularly, to a protective structure for ion conductive channel of an electrolyte membrane in a lithium-ion secondary battery which is applied with lithium compounds having a specific structure of orientation on the surface of lithuim metal thin film formed on the surface of a specific lithium compound electrolyte, in order to reduce the interfacial resistance of battery cells, thus improving the performance of the battery cells.

Description

Structure for Ionic Conductive Way of Electrolyte Membrane in Lithium Ion Secondary Battery in Lithium Ion Secondary Battery

The present invention relates to an ion conduction passage structure for a thin film of a lithium compound applied as an electrolyte of a lithium ion battery, and more particularly, to a lithium metal thin film contacting a specific lithium compound electrolyte in a structure having an orientation with a lithium compound. The present invention relates to an ion conductive path protection structure of a lithium compound electrolyte thin film which improves battery performance by reducing interfacial resistance.

A secondary battery using lithium ions is a device that converts the chemical energy difference when lithium ions are located at the negative electrode and the positive electrode into electrical energy, and separates a passage through which an electron current flows and a passage through which an ion current flows.

In the existing technology, a liquid electrolyte in which lithium cations and opposite anions are dissolved in a solvent is used to form a passage through which an ionic current flows, that is, a lithium cation conducts, but an electron current does not flow. That is, the liquid electrolyte is one of battery components in which lithium ions easily move and electrons inhibit movement. Liquid electrolytes using organic solvents require airtight design to prevent leakage and evaporation, and if a short circuit occurs inside the secondary battery, it becomes a fuel source in the event of a fire, and the liquid is used to increase the stability and efficiency (ion conductivity) of the secondary battery. Efforts have been extensively made to substitute solid ion conductors or gel type ion conductors to replace electrolytes.

As described above, the lithium ion battery separates the flow of current into a circuit through which an electron current flows and an electrolyte portion through which an electron cannot flow but only an ion current in order to convert chemical energy when lithium is located at the anode and cathode. Most existing batteries have been using liquid electrolyte because they must. By the way, the liquid electrolyte has a high ionic conductivity of about 10 ^-2 S / cm at room temperature, but contains a liquid containing an organic solvent inside the device has a lot of weak chemical / mechanical stability.

In order to overcome the shortcomings of the liquid electrolyte, a gel-type polymer electrolyte has been applied. However, the polymer electrolyte also contains an organic solvent, and if a problem such as an internal short circuit occurs in the battery, it becomes a flammable fuel and impairs battery safety.

In addition, in order to overcome the weaknesses of liquid and polymer electrolytes, non-flammable solid electrolytes have been developed. Some derivatives of typical solid electrolytes, LISICon and Thio-LISICon, have been reported to exhibit ionic conductivity close to liquid electrolyte at room temperature. In order to improve ion solidification properties, doping methods using various elements have been tried. That is, since solid electrolytes have high stability and low ion conductivity, various efforts are being made to replace external elements in a material structure or artificially induce defects in order to increase ion conductivity. Recently, a Ge-doped Li ₁₀ GeP ₂ S ₁₂ structure (named LGPS) has been reported to approximate the ionic conductivity of a liquid electrolyte at room temperature, which is partly in the c-axis direction of the cubic lattice. As a structure with filled one-dimensional conduction passages, the conductivity of solid electrolytes was reported to be close to 10 ⁻² Scm ⁻¹ and to be electrochemically stable (Kamaya et al. Nature Mat., 2011).

On the other hand, in connection with the improvement of the electrolyte performance of a lithium ion secondary battery, various patent documents have been published.

Japanese Laid-Open Patent Publication No. 2011-9130 proposes a structure in which the crystal orientation of each component is limited in order to solve the integration problem due to the difference in thermal expansion rate of the positive electrode, the negative electrode, and the solid electrolyte with respect to the all-solid lithium secondary battery. In the related art, a battery structure in which a positive electrode and a negative electrode are disposed on both sides of a solid electrolyte powder layer is proposed in relation to an all-solid battery.

In addition, Japanese Laid-Open Patent Publication No. 2009-20687 proposes a technique employing a step of simultaneously baking a solid electrolyte molded green body and a positive / cathode molded green body at a high temperature as a method of manufacturing an ion secondary battery. In 2010-282803, a method for producing an all-solid lithium ion secondary battery has been proposed, in which a solid electrolyte powder charged with charge is blown out together with a carrier gas to form a solid electrolyte layer.

In addition, Korean Patent No. 10-659049 discloses a technique related to the basic composition and additive application composition of a glass solid electrolyte as an inorganic solid electrolyte, and Japanese Patent Laid-Open No. 2012-48973 proposes a sulfide-based solid electrolyte and an Iodine doping method. In Japanese Patent Laid-Open No. 2008-21416, an oxide sulfide mixed solid electrolyte composition is proposed, and Japanese Patent Laid-Open No. 2005-228570 proposes a method for producing a solid electrolyte having a Li ₂ SP ₂ S ₅ composition.

However, these conventional patent documents are about composition optimization, process optimization, and battery structure to improve material properties, and there is a lack of a fundamental causal approach to interfacial resistance, which is a major problem in solid electrolytes. There was a limit in improving battery performance through improvement of interface resistance.

1. Japanese Laid-Open Patent No. 2011-9130 2. Japanese Patent Laid-Open No. 2011-150817 3. Japanese Patent Publication No. 2009-20687 4. JP 2010-282803 A 5. Korean Patent No. 10-659049 6. Japanese Patent Publication No. 2012-48973 7. Japanese Patent Application Publication No. 2008-21416 8. JP 2005-228570

As a result of a long study to solve the above problems of improving the performance of the lithium ion secondary battery, it is necessary to identify the ion conduction mechanism of the solid electrolyte and to control the orientation of the material to minimize the ion transfer resistance in the system. It was. Therefore, the lithium compound constituting the electrolyte is composed of Li ₃ PS ₄ solid electrolyte and the lithium metal thin film introduced into the lithium compound electrolyte thin film, not the doped structure of external new atoms as in the previous attempt, is coated with the lithium compound to have an orientation 1 The present invention has been completed by knowing that the battery performance is greatly improved by constructing a device structure or an interface structure in which the dimensional ion conduction passage is well preserved.

Accordingly, an object of the present invention is to provide an ion conductive path protection structure of a lithium compound electrolyte thin film coated with a lithium compound to have an orientation on a lithium metal thin film introduced into a lithium compound solid electrolyte thin film in a lithium ion secondary battery.

In addition, an object of the present invention is to provide a lithium ion secondary battery having improved orientation of the lithium compound solid electrolyte thin film is applied to the ion conductive path protection structure to improve the battery performance.

In order to solve the above problems, the present invention is a solid electrolyte is disposed between the cathode and the anode and the electrolyte electrolyte thin film between the solid electrolyte and the anode and the anode respectively disposed in the lithium ion secondary battery, the solid electrolyte is Li ₃ PS ₄ The electrolyte thin film provides an ion conductive path protection structure of a lithium compound electrolyte thin film having a structure in which Li ₃ PS ₄ is coated on a lithium thin film to have an orientation in the same direction as a lithium ion moving direction.

In addition, the present invention is a lithium ion secondary battery in which a solid electrolyte is disposed between the negative electrode and the positive electrode and an electrolyte thin film is disposed between the solid electrolyte and the negative electrode and the positive electrode, wherein the electrolyte thin film is ion conductivity of the lithium compound electrolyte thin film as described above. Provided is a lithium ion secondary battery including a passage protection structure.

Unlike the conventional method, the ion conductive path protection structure of the lithium compound electrolyte thin film in the lithium secondary battery according to the present invention is coated with Li ₃ PS ₄ on the lithium thin film of the electrolyte thin film to have an orientation in the same direction as the lithium ion moving direction. Since the ion channel forms a desirable structure of the ion channel to effectively transfer Li ions in the lithium anode and the Li ₃ PS ₄ material to reduce the interface resistance, the electrode / electrolyte interface among the electrolyte resistance, electrode resistance, and electrode / electrolyte interface resistance Reducing the resistance has the effect of significantly improving battery performance.

1 is a conceptual diagram showing a transfer path of Li ions in the Li ₃ PS ₄ structure, (a) is a general aggregate structure of Li ₃ PS ₄ , (b) is a structural feature of the Li ion transfer path in each unit structure Conceptually represented.
FIG. 2 is a graph showing the results of measurement of the moving energy per path coordinate of an electrolyte membrane, which is a migration barrier of Li ions, as a result of Density Function Theory calculation obtained using Perdew-Burke-Ernzerhof functional Functional.
3 is a structure of a lithium ion secondary battery to which a solid electrolyte is applied and a structure of a lithium ion secondary battery in which a Li ₃ PS ₄ solid electrolyte is disposed between a negative electrode and a positive electrode.
FIG. 4 is a structure diagram of a lithium ion secondary battery in which a Li ₃ PS ₄ solid electrolyte thin film having an alignment between a positive electrode active material, a solid electrolyte interface, and a negative electrode active material and a solid electrolyte interface is disposed in a lithium ion secondary battery structure using a solid electrolyte.
FIG. 5 is an enlarged structure of an interface between the active material and the solid electrolyte of FIG. ₄ , in which a Li ₃ PS ₄ solid electrolyte thin film is inserted. (a) shows a structure in which the Li ₃ PS ₄ coating layer is applied without orientation, and in case of (b), the Li ₃ PS ₄ coating layer is formed such that the Li ₃ PS ₄ coating layer is aligned.
6 is a schematic diagram of an interface circuit model for an active material-electrolyte for an electrode structure. This circuit diagram also serves as a model for analyzing the resistance of battery components during battery operation.
7 is a graph comparing the measured values of the interfacial resistance in the battery of the Example and Comparative Example by the impedance analysis by the impedance fitting in Experimental Example 1 of the present invention. Arrows in the diagram indicate the interface resistance component confirmed by analyzing the impedance using the circuit diagram of FIG. 6.

Hereinafter, the present invention will be described in more detail.

According to the present invention, in a lithium ion secondary battery in which a solid electrolyte is disposed between a cathode and an anode and an electrolyte thin film is disposed between the solid electrolyte and the cathode and the anode, the solid electrolyte is a material having lithium ion conductivity and may have LISICon and thio-LISICon. Reported solid electrolytes such as, Perovskitre and Garnet can be used. The Li ₃ PS ₄ thin film is disposed between the active material and the solid electrolyte, and the electrolyte thin film relates to a structure coated so as to have an orientation in the same direction as a lithium ion moving direction in Li ₃ PS ₄ .

The present invention is Li ₃ PS ₄ when manufacturing the device It is a technique to prevent one-dimensional lithium ion conduction passages from clogging by allowing excessive Li ions to be applied to the interface of the lithium thin film at the interface where the interface of the solid electrolyte of the series contacts the surface of the cathode and the anode.

In general, the LGPS structure is partially occupied by Li ions (69% and 64%), and thus there is a one-dimensional conduction passage that facilitates lithium ion transfer. Li ₃ PS ₄ There is a one-dimensional conduction passage in the b-axis direction, partially occupied by Li ions (68%, 28%), and the diffusion barrier energy of Li ions between the partially occupied positions is 0.1 eV or less. Maintaining this one-dimensional conduction path of Li ions at the actual device fabrication stage is a key technology for optimizing lithium ion transfer, and doping of external atoms with different ion radii maintains this phenomenon. In this technical principle, the present invention is a structure in which the ion transport conditions of the lithium ion channel are optimized.

Lithium-Tetrathiophosphate (Li ₃ PS ₄ ) solid structure used as a solid electrolyte in the technology related to the fabrication of ion conductive membranes based on the movement of lithium ions is an excellent solid type Li ion conducting material and various doping methods This has been developed. In particular, there is a one-dimensional conduction passage in which Li ions are partially filled in the b-axis direction of the crystal structure. If the Li can partially use the one-dimensional conductive passage partially filled, it is possible to realize a good Li ion conductive film without additional external ion doping.

Therefore, in the present invention, in order to maintain the preferential one-dimensional ion conduction passage in the material for improving the ion conductivity in the battery using the Thio-LISICon-based Li ₃ PS ₄ , a new atom-doped structure attempted in the prior art is not implemented. It is characterized by the newly constructed interfacial structure having a well-maintained orientation so that the ion transport passage of the material works well in the battery structure.

In the present invention, in order to confirm the transfer path of Li ions in the Li ₃ PS ₄ structure, the energy barrier according to the propagation of Li ions is confirmed through computational science. The route was found to have the same structural characteristics as in FIG. 1. That is, in the Li ₃ PS ₄ structure, the transfer path of Li ions is that in the general assembly structure of Li ₃ PS ₄ of FIG. 1 (a), each unit structure has a Li ion transfer path as shown in FIG. 1 (b).

In this regard, the results of Density Function Theory calculation obtained using Perdew-Burke-Ernzerhof functional Functional are shown in FIG. 2. As can be seen from the graph of FIG. 2, the transfer energy per path coordinate of the electrolyte membrane, which is a migration barrier of partially occupied Li ions, is very small, 0.1 eV or less. Therefore, the partially occupied Li ions on the chain line, which is a one-dimensional assembly structure, can easily move along the chain line in the b-axis direction, i.

Based on the theoretical background according to the present invention, it is necessary to control the orientation of Li ₃ PS ₄ in order to maximize the movement of Li ions in the battery to which Li ₃ PS ₄ is applied. This is because, when the lithium anode and Li ₃ PS ₄ does not have a specific orientation, a local Li ion rich phase is formed and a difference in mobility of Li ions occurs to increase the interfacial resistance as a whole. Therefore, when an Li negative electrode and Li ₃ PS ₄ lithium-ion movement path (010) plane is Li ₃ PS ₄ the growth so as to have an orientation in the same direction as the direction of movement of the lithium ions in contact with a lithium negative electrode and Li ₃ PS ₄ material within In this case, Li ions are effectively transferred to reduce interfacial resistance.

As such, in the present invention, in a lithium ion secondary battery in which a solid electrolyte is disposed between a cathode and an anode and an electrolyte thin film is disposed between the solid electrolyte and the anode and the cathode, the solid electrolyte is composed of Li ₃ PS ₄ and the electrolyte The thin film has a structure in which Li ₃ PS ₄ is coated to have an orientation in the same direction as a lithium ion moving direction.

When explaining the electrode structure of the present invention in more detail as follows.

In the all-solid-state battery structure in which a typical Li ₃ PS ₄ is applied as an electrolyte, a lithium ion battery installed such that the b-axis direction of the Li ₃ PS ₄ is directed from the negative electrode 1 to the positive electrode 2 of the lithium ion battery is shown in FIG. 3. Here, a structure in which a Li ₃ PS ₄ solid electrolyte 3 is disposed between the cathode 1 and the anode 2 is shown.

In the electrode structure of FIG. 3, an electrolyte membrane 4 of a lithium thin film is disposed between the Li ₃ PS ₄ solid electrolyte 3 and each of the anode 1 and the anode 2 adjacent to each other. . In FIG. 4, an electrolyte membrane (lithium thin film) is formed on both sides of the solid electrolyte. In the present invention, an additional Li is excessively coated with Li ₃ PS ₄ on each side of the interface of each of the electrolyte membranes ₄ . It has a structure.

The structure in which the Li ₃ PS ₄ coating layer 5 is further applied to the interface of the Li thin film 4 is shown in FIG. 5.

In FIG. 5 (a), the Li ₃ PS ₄ coating layer 5 is additionally coated, but the structure is applied without the orientation and the Li ion rich phase 6 is formed at the interface thereof. In FIG. 5 (a), the Li ₃ PS ₄ coating layer 5 has no orientation and a Li ion rich phase 6 is formed at some interfaces due to a difference in lithium ion transfer rate in the coating layer. In the Li ₃ PS ₄ coating layer 5, the local resistance is increased due to the difference in ion transfer characteristics between the portions where the Li ion rich phase 6 is formed and the portions where the Li ion rich phase 6 is not formed, thereby increasing the reaction rate of the entire battery. There is a problem that is lowered.

However, FIG. 5 (b) shows a structure in which the Li ₃ PS ₄ coating layer 55 is formed on the lithium thin film 44 so as to have an orientation. Figure 5 (b) The Li ₃ PS _4, because the coating layer 55 is has an orientation defined structure because Li ions rich face (Rich Phase) is of a uniform surface without a space be formed of Li ₃ PS ₄ coated layers ( The same ion mobility is exhibited over the entire surface of 55).

The structure having the orientation of FIG. 5 (b) of the present invention is such that the orientation of the voltage is applied when the Li ₃ PS ₄ coating layer 55 is formed on the lithium thin film 44. For example, in the process of forming a coating layer by sputtering Li ₃ PS ₄ powder by a sputtering method on a conventional lithium thin film, sputtering while applying a voltage in the range of 200-400 Volt to both sides of the thin film has an easy orientation. A Li ₃ PS ₄ coating layer is formed.

As mentioned above. According to the present invention, in a lithium ion secondary battery in which a solid electrolyte is disposed between a cathode and an anode and an electrolyte thin film is disposed between the solid electrolyte and the anode and the anode, the lithium electrolyte is composed of Li ₃ PS ₄ and the electrolyte thin film is a lithium thin film. Li ₃ PS ₄ is coated with Li ₃ PS ₄ applied while applying a voltage so that Li ₃ PS ₄ has an orientation in the same direction as the lithium ion moving direction, thereby forming an electrolyte thin film having a Li ₃ PS ₄ coating layer formed thereon. By applying it in a thin film, it can manufacture with the lithium ion secondary battery of the preferable performance excellent in performance compared with the conventional battery.

The interface circuit model for the active material-electrolyte for the electrode structure of the present invention thus prepared is shown in FIG. 6. In the circuit model of FIG. 6, the electrode structure of the present invention, which provides orientation to the interface, maintains a lithium ion channel in a preferred shape and protects the channel as compared with the case where there is no orientation. As a result, the interfacial resistance is greatly lowered, thereby significantly improving battery performance.

Accordingly, the present invention provides a lithium ion secondary battery in which a solid electrolyte is disposed between a cathode and an anode, and an electrolyte thin film is disposed between the solid electrolyte and the anode and the anode, respectively, wherein the lithium compound is configured to have an orientation as described above. It includes a lithium ion secondary battery having an ion conductive path protection structure of an electrolyte thin film.

As described above, the electrode structure according to the present invention analyzes the lithium ion transfer mechanism in the solid electrolyte and controls the orientation of the electrolyte membrane in order to improve the lithium ion transfer resistance between the active material and the solid electrolyte, thereby analyzing the impedance of the lithium ion secondary battery. In the case of the battery structure that controls the orientation of the electrolyte, it can be seen that the interface resistance is improved compared to the electrode structure without the orientation.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

Example

A lithium ion secondary battery comprising a Li ₃ PS ₄ solid electrolyte disposed between a negative electrode and a positive electrode and an electrolyte thin film disposed between the solid electrolyte and the negative electrode and the positive electrode as a Li thin film (foil), respectively, is prepared as an electrolyte thin film. Was prepared by forming a Li ₃ PS ₄ coating layer having an orientation on one side of a Li thin film under a vacuum, Ar atmosphere, and 200-400 V bias conditions in a 200 um thick Li foil, and applying the same as the electrolyte thin film. The battery was prepared.

Comparative Example

But the same procedure as in the above embodiment by sintering seupeot under the same conditions nor not conducted to give a voltage is applied in the process of forming the Li ₃ PS ₄ coating layer on Li thin film is applied to the electrolyte film forms a Li ₃ PS ₄ coating layer It was applied to battery manufacturing.

Experimental Example 1

Measuring the impedance of the battery while applying a voltage of 10 mV in the AC frequency range of 1 MHz to 0.1 Hz for each lithium ion secondary battery prepared in the above Examples and Comparative Examples and using the equivalent circuit described in FIG. The measurements were compared. These impedance analysis results are shown as a comparative graph in FIG. The analysis results shown in FIG. 7 show that the interface resistance is significantly improved in the case of having the orientation control film (Example) compared to the case of applying the non-oriented film (Comparative Example).

Experimental Example 2

In order to confirm the performance of the lithium ion secondary battery according to the above Examples and Comparative Examples, the physical properties such as charge / discharge evaluation, life characteristics, etc. were compared under the same conditions as in Experimental Example 1. At this time, the experimental method was carried out under 1/20 C condition by constant current method respectively.

The results are shown in Table 1 below.

Metrics Example Comparative Example Primary discharge amount (mAh / g_s) 800 700 Life characteristics
(Remaining capacity / initial capacity after life evaluation) 60% after 40 times 45% after 40 times

As shown in Table 1, the embodiment in which the orientation control film was applied as the electrolyte membrane showed an improvement of 10% or more in the physical properties such as the primary discharge amount and the life characteristics compared to the comparative example in which the non-oriented film was applied. It was determined that the suppression of ion transfer was partially eliminated, and the interface clogging phenomenon was suppressed as the life progressed, and it was confirmed that the battery having the ion conductive path protection structure of the lithium compound electrolyte thin film according to the present invention exhibited excellent battery performance.

1-cathode
2-anode
3-solid electrolyte
4-electrolyte membrane
44-Lithium Thin Film
5, 55-Li ₃ PS ₄ coating layer
6-Li ₃ PS ₄ Rich Face

Claims (3)

In a lithium ion secondary battery in which a solid electrolyte is disposed between a negative electrode and a positive electrode and an electrolyte thin film is disposed between the solid electrolyte and the negative electrode and the positive electrode, the solid electrolyte is composed of Li ₃ PS ₄ , and the electrolyte thin film is formed on a lithium thin film. An ion conductive path protection structure of a lithium compound electrolyte thin film in a lithium ion secondary battery, characterized in that the Li ₃ PS ₄ is coated so as to have an orientation in the same direction as the lithium ion moving direction.
The ion conductive path protection structure of claim 1, wherein the coated structure having the orientation is a structure formed by applying a voltage.
In a lithium ion secondary battery in which a solid electrolyte is disposed between a negative electrode and a positive electrode and an electrolyte thin film is disposed between the solid electrolyte and the negative electrode and the positive electrode, the electrolyte thin film is an ion conductive path protection structure of the lithium compound electrolyte thin film of claim 1. Lithium-ion secondary battery comprising a.

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